TABLE OF CONTENTS (HIDE)

Java Programming Tutorial

Yet Another Exercises on Java Basics

These exercises are meant for submission to my online submission system.

Getting Started Exercises

Add Two Integers (Add2Integer.java) (Getting Started)

Write a program called Add2Integers that prompts user to enter two integers. The program shall read the two integers as type int; compute their sum; and print the result.

Test Cases

1

5
8

Enter first integer: 
Enter second integer: 
The sum is: 13

2

-5
-8

Enter first integer: 
Enter second integer: 
The sum is: -13

3

8
-8

Enter first integer: 
Enter second integer: 
The sum is: 0

4

8
0

Enter first integer: 
Enter second integer: 
The sum is: 8

5

-8
0

Enter first integer: 
Enter second integer: 
The sum is: -8

6

0
0

Enter first integer: 
Enter second integer: 
The sum is: 0

Hints

import java.util.Scanner;   // For keyboard input
/**
 * 1. Prompt user for 2 integers
 * 2. Read inputs as "int"
 * 3. Compute their sum
 * 4. Display the result
 */
public class Add2Integers {  // Save as "Add2Integers.java"
   public static void main (String[] args) {
      // Declare variables
      int number1, number2, sum;
      Scanner in = new Scanner(System.in);  // Scan the keyboard for input

      // Put up prompting messages and read inputs as "int"
      System.out.print("Enter first integer: ");  // No newline for prompting message
      number1 = in.nextInt();                     // Read next input as "int"
      System.out.print("Enter second integer: ");
      number2 = in.nextInt();

      // Compute sum
      sum = number1 + number2;

      // Display result
      System.out.println("The sum is: " + sum);   // Print with newline
      in.close();  // Close Scanner
   }
}

Odd or Even (OddEven.java) (if-else and modulus)

Write a program called OddEven that prompts user for an integer. The program shall read the input as an int; and check if the integer is odd or even.

Test Cases

1

99 

Enter an integer:  
99 is odd 
bye 

2

88 

Enter an integer:  
88 is even 
bye 

3

0 

Enter an integer:  
0 is even 
bye 

4

-1 

Enter an integer:  
-1 is odd 
bye 

5

-4 

Enter an integer:  
-4 is even 
bye 

Hints:

      // Declare variables
      int numberIn;   // input integer
      ......
      // Prompt and read input as "int"
      ......

      // Check odd/even and print result
      // Use % to find the remainder dividing by 2, and compare with 0
      if (numberIn % 2 == 0) {      // double-equal for comparison
         System.out.println(......);
      } else {
         System.out.println(......);
      }

Multiple (Multiple.java) (if-else and modulus)

Write a program called Multiple that prompts user for 2 integers. The program shall read the inputs as int; and check if the first integer is a multiple of the second integer.

Test Cases

1

99
11

Enter 1st integer: 
Enter 2nd integer: 
99 IS a multiple of 11

2

99
12

Enter 1st integer: 
Enter 2nd integer: 
99 IS NOT a multiple of 12

3

5
10

Enter 1st integer: 
Enter 2nd integer: 
5 IS NOT a multiple of 10

Hints

1. Use two int variables: number1 and number2 to store the inputs.
2. Use modulus operator % to find the remainder and compare with zero, i.e., if (number1 % number2 == 0) .... Take note that comparison operator is double-equal.

Arithmetic and Min/Max of 3 integers (SumProductMinMax3.java) (if-else and min/max)

Write a program called SumProductMinMax3 that prompts user for three integers. The program shall read the inputs as int; compute the sum, product, minimum and maximum of the three integers; and print the results.

Test Cases

1

3
2
8

Enter 1st integer: 
Enter 2nd integer: 
Enter 3rd integer: 
The sum is: 13
The product is: 48
The min is: 2
The max is: 8

2

44
22
99

Enter 1st integer: 
Enter 2nd integer: 
Enter 3rd integer: 
The sum is: 165
The product is: 95832
The min is: 22
The max is: 99

3

199
-199
0

Enter 1st integer: 
Enter 2nd integer: 
Enter 3rd integer: 
The sum is: 0
The product is: 0
The min is: -199
The max is: 199

Hints

      // Declare variables
      int number1, number2, number3;  // The 3 input integers
      int sum, product, min, max;     // To compute these
      Scanner in = new Scanner(System.in);  // Scan the keyboard

      // Prompt and Read inputs as "int"
      ......

      // Compute sum and product
      sum = ......
      product = ......

      // Compute min
      // The "coding pattern" for computing min is:
      // 1. Set min to the first item
      // 2. Compare current min with the second item and update min if second item is smaller
      // 3. Continue for the next item
      min = number1;        // Assume min is the 1st item
      if (number2 < min) {  // Check if the 2nd item is smaller than current min
         min = number2;     // Update min if so
      }
      if (number3 < min) {  // Continue for the next item
         min = number3;
      }

      // Compute max - similar to min
      ......

      // Print results
      ......

Arithmetic and Min/Max of 5 integers (SumProductMinMax5.java) (if-else and min/max)

Write a program called SumProductMinMax5 that prompts user for five integers. The program shall read the inputs as int; compute the sum, product, minimum and maximum of the five integers; and print the results.

Test Cases

1

5
1
2
4
3

Enter 1st integer: 
Enter 2nd integer: 
Enter 3rd integer: 
Enter 4th integer: 
Enter 5th integer: 
The sum is: 15
The product is: 120
The min is: 1
The max is: 5

2

-999
99
88
1
0

Enter 1st integer: 
Enter 2nd integer: 
Enter 3rd integer: 
Enter 4th integer: 
Enter 5th integer: 
The sum is: -811
The product is: 0
The min is: -999
The max is: 99

Hints

See previous question. Use five int variables: number1, number2, ..., number5 to store the inputs.

Print Day in Word (PrintDayInWord.java) (nested-if)

Write a program called PrintDayInWord that prompts user for an integer 0, 1, 2, ..., 6, or other. The program shall read the input as int; and print "Sunday", "Monday", ..., "Saturday", or "Not a valid day", respectively. You are required to use a "nested-if" statement in this program.

Test Cases

1

0

Enter the day number: 
Sunday
bye

2

6

Enter the day number: 
Saturday
bye

3

9

Enter the day number: 
Not a valid day
bye

Hints

      // Declare variables
      int dayNumber;   // The input number
      ......
      // Prompt and read input as "int"
      ......

      // Using nested-if to handle the 8 cases (0 to 6 and others)
      if (dayNumber == 0) {   // double-equal for comparison
         ......
      } else if (dayNumber == 1) {
         ......
      } else if (......) {
         ......
      } else {
         ......
      }

Print Number in Word (PrintNumberInWord.java) (switch-case)

Write a program called PrintNumberInWord that prompts user for an integer 0, 1, 2, ..., 9, or other. The program shall read the input as int; and print "ZERO", "ONE", "TWO", ..., "NINE", or "OTHER", respectively. You are required to use a "switch-case" statement in this program.

Test Cases

1

0

Enter a number: 
ZERO
bye!

2

6

Enter a number: 
SIX
bye!

3

-1

Enter a number: 
OTHER
bye!

Hints

      // Declare variables
      int numberIn;   // The input number
      ......

      // Using switch-case to handle 11 cases (0 to 9 and others)
      switch (numberIn) {
         case 1:
            System.out.println(...); break;  // "break" needed at the end of every "case"
         case 2:
            System.out.println(...); break;
         ......;
         ......;
         default:
            ......;  // "break" not needed for "default"
      }

Rectangle Computation (RectangleComputation.java) (Type int)

Write a program called RectangleComputation that prompts user for the length and width of a rectangle in integer. The program shall read the inputs as int; compute the perimeter and area of the rectangle; and print the results.

Test Cases

1

9 
8 

Enter the length:  
Enter the width:  
The perimeter is: 34 
The area is: 72 

2

8 
9 

Enter the length:  
Enter the width:  
The perimeter is: 34 
The area is: 72 

3

1 
1 

Enter the length:  
Enter the width:  
The perimeter is: 4 
The area is: 1 

Hints

Use int variables length, width, area, perimeter to store the inputs and results.

Circle Computation (CircleComputation.java) (Type double and printf())

Write a program called CircleComputation that prompts user for the radius of a circle in floating point number. The program shall read the input as double; compute the diameter, circumference, and area of the circle in double; and print the values rounded to 2 decimal places. Use System-provided constant Math.PI for pi.

The formulas are:

   area = Math.PI * radius * radius;
   diameter = 2.0 * radius;
   circumference = 2.0 * Math.PI * radius;

Test Cases

1

1.2

Enter the radius: 
Surface Area is: 18.10
Volume is: 7.24

2

1

Enter the radius: 
Surface Area is: 12.57
Volume is: 4.19

3

0.12e2

Enter the radius: 
Surface Area is: 1809.56
Volume is: 7238.23

4

0

Enter the radius: 
Surface Area is: 0.00
Volume is: 0.00 

Hints

1. Use double variables radius, diameter, circumference and area to store the input and results.
2. Use in.nextDouble() to read a double.
3. Use System.out.printf() with specifier %.2f to print a double, rounded to 2 decimal places; and %n to print a newline. For example,

   System.out.printf("Diameter is: %.2f%n", diameter);

Sphere Computation (SphereComputation.java) (Type double and printf())

Write a program called SphereComputation that prompts user for the radius of a sphere in floating point number. The program shall read the input as double; compute the volume and surface area of the sphere in double; and print the values rounded to 2 decimal places. Use System-provided constant Math.PI for pi.

The formulas are:

   surfaceArea = 4 * Math.PI * radius * radius;
   volume = 4 /3 * Math.PI * radius * radius * radius;   // But this does not work?! Why?

Test Cases

1

1.2

Enter the radius: 
Surface Area is: 18.10
Volume is: 7.24

2

1

Enter the radius: 
Surface Area is: 12.57
Volume is: 4.19

3

0.12e2

Enter the radius: 
Surface Area is: 1809.56
Volume is: 7238.23

4

0

Enter the radius: 
Surface Area is: 0.00
Volume is: 0.00 

Hints

1. Use double variables radius, volume and surfaceArea to store the input and results.
2. Use in.nextDouble() to read a double.
3. Use System.out.printf() with specifier %.2f to print a double rounded to 2 decimal places; and %n to print a newline. For example,

   System.out.printf("Volume is: %.2f%n", volume);

Cylinder Computation (CylinderComputation.java) (Type double and printf())

Write a program called CylinderComputation that prompts user for the base radius and height of a cylinder in floating point number. The program shall read the inputs as double; compute the base area, surface area, and volume of the cylinder; and print the values rounded to 2 decimal places. Use System-provided constant Math.PI for pi.

The formulas are:

   baseArea = Math.PI * radius * radius;
   surfaceArea = 2.0 * Math.PI * radius * height + 2.0 * baseArea;
   volume = baseArea * height;

Test Cases

1

1
1

Enter the radius: 
Enter the height: 
Base area is: 3.14
Surface area is: 12.57
Volume is: 3.14

2

1.1
2.2

Enter the radius: 
Enter the height: 
Base area is: 3.80
Surface area is: 22.81
Volume is: 8.36

3

3
1.1e2

Enter the radius: 
Enter the height: 
Base area is: 28.27
Surface area is: 2130.00
Volume is: 3110.18 

Hints

1. Use double variables radius, height, baseArea, surfaceArea and volume to store the inputs and results. Take note that spaces are not allowed in names.
2. Use in.nextDouble() to read a double.
3. Use System.out.printf() with specifier %.2f to print a double, rounded to 2 decimal places; and %n to print a newline. For example,

   System.out.printf("Base Area is: %.2f%n", baseArea);

Swap Contents of Two Variables (SwapIntegers.java) (swap contents)

Write a program called SwapIntegers that prompts user for two integers. The program shall read the inputs as int, save in two variables called number1 and number2; swap the contents of the two variables; and print the results.

Test Cases

1

5
8

Enter first integer: 
Enter second integer: 
After the swap, first integer is: 8, second integer is: 5

2

9
-9

Enter first integer: 
Enter second integer: 
After the swap, first integer is: -9, second integer is: 9

3

11
11

Enter first integer: 
Enter second integer: 
After the swap, first integer is: 11, second integer is: 11

Hints

To swap the contents of two variables x and y, you need to introduce a temporary storage, say temp, and do:

temp <- x
x <- y
y <- temp

Decisions and Loops

Sum and Average of Running Integers (SumAverage.java) (for-loop)

Write a program called SumAverage that prompts user for a lowerbound and an upperbound. The program shall read the inputs as int; compute the sum (in int) and average (in double) of the running integers from the lowerbound to the upperbound (both inclusive); and print the sum (int) and average (double) rounded to 2 decimal places.

Test Cases

1

1
100

Enter the lowerbound: 
Enter the upperbound: 
The sum is: 5050
The average is: 50.50

2

1
1000

Enter the lowerbound: 
Enter the upperbound: 
The sum is: 500500
The average is: 500.50

3

10
999

Enter the lowerbound: 
Enter the upperbound: 
The sum is: 499455
The average is: 504.50

4

-5
5

Enter the lowerbound: 
Enter the upperbound: 
The sum is: 0
The average is: 0.00

Hints

      // Declare variables
      int lowerbound, upperbound, sum = 0;
      double average;
      ......

      // Prompt and read inputs as "int"
      ......

      // Compute sum using a for-loop
      for (int number = ...; number <= ...; ++number) {
         sum += number;
      }

      // Compute average
      // Take note that int/int gives int. Type casting needed.
      // The total count is (upperbound - lowerbound + 1)
      average = ......

      // Display results
      ......

Factorial (Factorial.java) (for-loop)

Write a program called Factorial that prompts user for an integer n and prints the factorial of n. Use an int to store the factorial. Assume that n <= 12 (because factorial of 13 is outside the range of int).

The formula is:

   factorial(n) = 1*2*3*4*...*n   // product of 1 to n

Test Cases

1

12

Enter an integer: 
The Factorial of 12 is: 479001600

2

5

Enter an integer: 
The Factorial of 5 is: 120

3

1

Enter an integer: 
The Factorial of 1 is: 1 

Hints

Use an int variable called product initialized to 1; and a for-loop to accumulate into the product.

Factorial in long (FactorialLong.java) (for-Loop & Type long)

Write a program called FactorialLong that prompts user for an integer n. The program shall read the input as an int; compute the factorial of n in long; and print the result.

In this exercise, we use a long to compute and store the factorial. Take note that with int, you can store factorial upto 12 (9 digits); with long, you can store factorial upto 20 (19 digits).

The formula is:

   factorial(n) = 1*2*3*4*...*n   // product of 1 to n

Test Cases

1

13

Enter an integer: 
The Factorial of 13 is: 6227020800

2

20

Enter an integer: 
The Factorial of 20 is: 2432902008176640000

3

1

Enter an integer: 
The Factorial of 1 is: 1 

Income Tax Calculator (IncomeTaxCalculator.java) (Decision)

The progressive income tax rate is mandated as follows: The first $20000 of taxable income is tax exempted; the next $20000 is taxed at 10%; the next $20000 is taxed at 20%; and the rest is taxed at 30%. For example, suppose that the taxable income is $85000, the income tax payable is $20000*0% + $20000*10% + $20000*20% + $25000*30%.

Write a program called IncomeTaxCalculator that reads the taxable income (in int). The program shall calculate the income tax payable (in double); and print the result rounded to 2 decimal places.

Test Cases

1

20000

Enter the taxable income: $
The income tax payable is: $0.00

2

20001

Enter the taxable income: $
The income tax payable is: $0.10

3

25000

Enter the taxable income: $
The income tax payable is: $500.00

4

40000

Enter the taxable income: $
The income tax payable is: $2000.00

5

50000

Enter the taxable income: $
The income tax payable is: $4000.00

6

60000

Enter the taxable income: $
The income tax payable is: $6000.00

7

85000

Enter the taxable income: $
The income tax payable is: $13500.00 

Hints

      // Declare constants first (variables may use these constants)
      // The keyword "final" marked these as constant (i.e., cannot be changed).
      // Use uppercase words joined with underscore to name constants
      final double TAX_RATE_ABOVE_20K = 0.1;
      final double TAX_RATE_ABOVE_40K = 0.2;
      final double TAX_RATE_ABOVE_60K = 0.3;

      // Declare variables
      int taxableIncome;
      double taxPayable;
      ......

      // Compute tax payable in "double" using a nested-if to handle 4 cases
      if (taxableIncome <= 20000) {         // [0, 20000]
         taxPayable = ......;
      } else if (taxableIncome <= 40000) {  // [20001, 40000]
         taxPayable = ......;
      } else if (taxableIncome <= 60000) {  // [40001, 60000]
         taxPayable = ......;
      } else {                              // [60001, ]
         taxPayable = ......;
      }
      ......

Pension Contribution Calculator (PensionContributionCalculator.java) (Decision)

The pension fund contribution of an employee is mandated as follows: For employee aged 55 and below, the employee contributes 20% of the monthly salary (subjected to a ceiling stated below) and the employer contributes 17%. For employee aged above 55 to 60, the employee contributes 13% and the employer contributes 13%. For employee aged above 60 to 65, the employee contributes 7.5% and the employer contributes 9%. For employee aged above 65, the employee contributes 5% and the employer contributes 7.5%. The salary ceiling that attracts contribution is capped at $6000. In other words, if an employee earns $6800, only $6000 attracts employee's and employer's contributions, the remaining $800 does not.

Write a program called PensionContributionCalculator that reads the monthly salary and the age (in int) of an employee. Your program shall calculate the employee's, employer's and total contributions (in double); and print the results rounded to 2 decimal places.

Test Cases

1

3000
30

Enter the monthly salary: $
Enter the age: 
The employee's contribution is: $600.00
The employer's contribution is: $510.00
The total contribution is: $1110.00

2

4123
55

Enter the monthly salary: $
Enter the age: 
The employee's contribution is: $824.60
The employer's contribution is: $700.91
The total contribution is: $1525.51

3

4123
56

Enter the monthly salary: $
Enter the age: 
The employee's contribution is: $535.99
The employer's contribution is: $535.99
The total contribution is: $1071.98

4

4123
60

Enter the monthly salary: $
Enter the age: 
The employee's contribution is: $535.99
The employer's contribution is: $535.99
The total contribution is: $1071.98

5

4123
61

Enter the monthly salary: $
Enter the age: 
The employee's contribution is: $309.22
The employer's contribution is: $371.07
The total contribution is: $680.30

6

4123
65

Enter the monthly salary: $
Enter the age: 
The employee's contribution is: $309.22
The employer's contribution is: $371.07
The total contribution is: $680.30

7

4123
66

Enter the monthly salary: $
Enter the age: 
The employee's contribution is: $206.15
The employer's contribution is: $309.22
The total contribution is: $515.38

8

6000
50

Enter the monthly salary: $
Enter the age: 
The employee's contribution is: $1200.00
The employer's contribution is: $1020.00
The total contribution is: $2220.00

9

8899
50

Enter the monthly salary: $
Enter the age: 
The employee's contribution is: $1200.00
The employer's contribution is: $1020.00
The total contribution is: $2220.00 

Hints

      // Declare constants
      final int SALARY_CEILING = 6000;
      final double EMPLOYEE_RATE_55_AND_BELOW = 0.2;
      final double EMPLOYER_RATE_55_AND_BELOW = 0.17;
      final double EMPLOYEE_RATE_55_TO_60 = 0.13;
      final double EMPLOYER_RATE_55_TO_60 = 0.13;
      final double EMPLOYEE_RATE_60_TO_65 = 0.075;
      final double EMPLOYER_RATE_60_TO_65 = 0.09;
      final double EMPLOYEE_RATE_65_ABOVE = 0.05;
      final double EMPLOYER_RATE_65_ABOVE = 0.075;

      // Declare variables
      int salary, age;     // to be input
      int contributableSalary;
      double employeeContribution, employerContribution, totalContribution;
      ......

      // Check the contribution cap
      contributableSalary = ......

      // Compute various contributions in "double" using a nested-if to handle 4 cases
      if (age <= 55) {         // 55 and below
         ......
      } else if (age <= 60) {  // (60, 65]
         ......
      } else if (age <= 65) {  // (55, 60]
         ......
      } else {                 // above 65
         ......
      }
      ......

Income Tax Calculator with Sentinel (IncomeTaxCalculatorSentinel.java) (Decision & Loop)

Based on the previous IncomeTaxCalculator, write a program called IncomeTaxCalculatorSentinel which shall repeat the calculations until user enter -1. This -1 is known as the sentinel (or terminating) value in programming.

Test Cases

1

12345
23456
45678
61234
89123
-1

Enter the taxable income (or -1 to end): $
The income tax payable is: $0.00
Enter the taxable income (or -1 to end): $
The income tax payable is: $345.60
Enter the taxable income (or -1 to end): $
The income tax payable is: $3135.60
Enter the taxable income (or -1 to end): $
The income tax payable is: $6370.20
Enter the taxable income (or -1 to end): $
The income tax payable is: $14736.90
Enter the taxable income (or -1 to end): $
bye!

2

98765
-1

Enter the taxable income (or -1 to end): $
The income tax payable is: $17629.50
Enter the taxable income (or -1 to end): $
bye!

3

-1

Enter the taxable income (or -1 to end): $
bye! 

Hints

      // Declare constants first
      final int SENTINEL = -1;    // Terminating value for input
      ......

      // Declare constants and variables
      int taxableIncome;
      double taxPayable;
      ......

      // Read the first input to "seed" the while loop
      System.out.print("Enter the taxable income (or -1 to end): $");
      taxableIncome = in.nextInt();

      while (taxableIncome != SENTINEL) {
         // Compute tax payable in "double" using a nested-if to handle 4 cases
         ......

         // Print result rounded to 2 decimal places
         ......

         // Read the next input
         System.out.print("Enter the taxable income (or -1 to end): $");
         taxableIncome = in.nextInt();
            // Repeat the loop body, only if the input is not the SENTINEL value.
            // Take note that you need to repeat these two statements inside/outside the loop!
      }
      System.out.println("bye!");

Pension Contribution Calculator with Sentinel (PensionContributionCalculatorSentinel.java) (Decision & Loop)

Test Cases

1

5123
51
5123
64
-1

Enter the monthly salary (or -1 to end): $
Enter the age: 
The employee's contribution is: $1024.60
The employer's contribution is: $870.91
The total contribution is: $1895.51
Enter the monthly salary (or -1 to end): $
Enter the age: 
The employee's contribution is: $384.22
The employer's contribution is: $461.07
The total contribution is: $845.30
Enter the monthly salary (or -1 to end): $
bye!

2

1234
21
-1

Enter the monthly salary (or -1 to end): $
Enter the age: 
The employee's contribution is: $246.80
The employer's contribution is: $209.78
The total contribution is: $456.58
Enter the monthly salary (or -1 to end): $
bye!

3

-1

Enter the monthly salary (or -1 to end): $
bye! 

Hints

      // Read the first input to "seed" the while loop
      System.out.print("Enter the monthly salary (or -1 to end): $");
      salary = in.nextInt();

      while (salary != SENTINEL) {
         // Read the rest of inputs
         System.out.print("Enter the age: ");
         age = in.nextInt();

         ......
         ......

         // Read the next input and repeat
         System.out.print("Enter the monthly salary (or -1 to end): $");
         salary = in.nextInt();
      }

Salesperson Salary (SalespersonSalary.java) (Decision & Loop)

A company pays its salesperson on a base-salary-plus-commission basis. A salesperson receives $1000 base salary plus 15% of their gross sales as commission. For example, a salesperson with gross sales of $18,000 receives $1000 + $18000*15%.

Write a program to compute the salary of ALL the salespersons in the company. Your program shall use a loop to continuously input each salesperson's gross sales (as int); compute that salesperson's salary (in double); and display the results rounded to 2 decimal places. The program shall terminate in response to input of -1.

Test Cases

1

10000
20000
30000
-1

Enter sales in dollars (or -1 to end): 
Salary is: $2500.00

Enter sales in dollars (or -1 to end): 
Salary is: $4000.00

Enter sales in dollars (or -1 to end): 
Salary is: $5500.00

Enter sales in dollars (or -1 to end): 
bye

2

12345
67890
-1

Enter sales in dollars (or -1 to end): 
Salary is: $2851.75

Enter sales in dollars (or -1 to end): 
Salary is: $11183.50

Enter sales in dollars (or -1 to end): 
bye

3

0
-1

Enter sales in dollars (or -1 to end): 
Salary is: $1000.00

Enter sales in dollars (or -1 to end): 
bye

4

-1

Enter sales in dollars (or -1 to end): 
bye 

Hints

      // Declare constants
      // The keyword "final" marked these as constant (i.e., cannot changed).
      // Use uppercase words joined with underscore to name constants
      final double BASE_SALARY = 1000;
      final double COMMISSION_RATE = 0.15;
      final int SENTINEL = -1;        // Terminating value for input

      // Declare variables
      int sales;       // Input gross sales
      double salary;   // Salary to be computed
      ......

      // Read the first input to "seed" the while loop
      System.out.print("Enter sales in dollars (or -1 to end): ");
      sales =  in.nextInt();

      while (sales != SENTINEL) {
         // Compute the salary in "double"
         ......

         // Print results rounded to 2 decimal places
         ......

         // Read the next input
         System.out.print("Enter sales in dollars (or -1 to end): ");
         sales =  in.nextInt();
         // Repeat the loop body, only if the input is not the SENTINEL value.
         // Take note that you need to repeat these two statements inside/outside the loop!
      }
      ......

Sales Tax (SalesTax.java) (Decision & Loop)

A sales tax of 7% is levied on all goods and services consumed. It is also mandatory that all the price tags should include the sales tax. For example, if an item has a price tag of $107, the actual price is $100 and $7 goes to the sales tax.

Write a program using a loop to continuously input the tax-inclusive price (as double); compute the actual price and the sales tax (in double); and print the results rounded to 2 decimal places. The program shall terminate in response to input of -1; and print the total price, total actual price, and total sales tax.

Test Cases

1

107
214
321
-1

Enter the tax-inclusive price in dollars (or -1 to end): 
Actual Price is: $100.00, Sales Tax is: $7.00

Enter the tax-inclusive price in dollars (or -1 to end): 
Actual Price is: $200.00, Sales Tax is: $14.00

Enter the tax-inclusive price in dollars (or -1 to end): 
Actual Price is: $300.00, Sales Tax is: $21.00

Enter the tax-inclusive price in dollars (or -1 to end): 
Total Price is: $642.00
Total Actual Price is: $600.00
Total Sales Tax is: $42.00

2

123
456
-1

Enter the tax-inclusive price in dollars (or -1 to end): 
Actual Price is: $114.95, Sales Tax is: $8.05

Enter the tax-inclusive price in dollars (or -1 to end): 
Actual Price is: $426.17, Sales Tax is: $29.83

Enter the tax-inclusive price in dollars (or -1 to end): 
Total Price is: $579.00
Total Actual Price is: $541.12
Total Sales Tax is: $37.88

3

1234.56
-1

Enter the tax-inclusive price in dollars (or -1 to end): 
Actual Price is: $1153.79, Sales Tax is: $80.77

Enter the tax-inclusive price in dollars (or -1 to end): 
Total Price is: $1234.56
Total Actual Price is: $1153.79
Total Sales Tax is: $80.77

4

-1

Enter the tax-inclusive price in dollars (or -1 to end): 
Total Price is: $0.00
Total Actual Price is: $0.00
Total Sales Tax is: $0.00 

Hints

      // Declare constants
      final double SALES_TAX_RATE = 0.07;
      final int SENTINEL = -1;        // Terminating value for input

      // Declare variables
      double price, actualPrice, salesTax;  // inputs and results
      double totalPrice = 0.0, totalActualPrice = 0.0, totalSalesTax = 0.0;  // to accumulate
      ......

      // Read the first input to "seed" the while loop
      System.out.print("Enter the tax-inclusive price in dollars (or -1 to end): ");
      price =  in.nextDouble();

      while (price != SENTINEL) {
         // Compute the tax
         ......
         // Accumulate into the totals
         ......
         // Print results
         ......

         // Read the next input
         System.out.print("Enter the tax-inclusive price in dollars (or -1 to end): ");
         price =  in.nextDouble();
         // Repeat the loop body, only if the input is not the sentinel value.
         // Take note that you need to repeat these two statements inside/outside the loop!
      }
      // print totals
      ......

Harmonics Sum (HarmonicSum.java) (Decision & Loop)

Write a program that prompts user for the maximum denominator (n). The program shall read the input as int; compute the sum of the Harmonic series upto n; and print the result (in full precision).

The Harmonic Series is:

   Sum = 1 + 1/2 + 1/3 + 1/4 + 1/5 + 1/6 + ..... + 1/n

You are to compute two sums: from left-to-right and from right-to-left. Also compute their absolute difference.

Test Cases

1

10000

Enter the max denominator: 
The sum from left-to-right is: 9.787606036044348
The sum from right-to-left is: 9.787606036044386
The absolute difference is: 3.730349362740526E-14

2

1000

Enter the max denominator: 
The sum from left-to-right is: 7.485470860550343
The sum from right-to-left is: 7.485470860550341
The absolute difference is: 2.6645352591003757E-15

3

1

Enter the max denominator: 
The sum from left-to-right is: 1.0
The sum from right-to-left is: 1.0
The absolute difference is: 0.0 

Hints

      // Declare variables
      int maxDenominator;   // to be input
      double sumL2R = 0.0, sumR2L = 0.0, absDiff;  // to compute these in "double"
      ......

      // Prompt and read inputs as "int"
      ......

      // Compute sum from left-to-right in "double"
      for (int denominator = 1; denominator <= maxDenominator; denominator++) {
         ......
         // Take note that int/int gives int.
      }

      // Compute sum from right-to-left in "double"
      for (int denominator = maxDenominator; denominator >= 1; denominator--) {
         ......
      }

      // Compute the absolute difference in "double"
      // absDiff = ......
      // if (absDiff < 0) absDiff = -absDiff;

      // Print results in full precision using println()
      ......

Compute PI (A) (ComputePIa.java) (Decision & Loop)

Write a program to compute the value of PI, using the following series:

   PI = 4 * (1 - 1/3 + 1/5 - 1/7 + 1/9 - 1/11 + 1/13 .....)

Your program shall prompt the user for the "maximum denominator" used in the computation.

Display the computed value of PI to 10 decimal places.

Test Cases

1

10000

Enter the maximum denominator: 
The PI computed is: 3.1413926536

2

1000

Enter the maximum denominator: 
The PI computed is: 3.1395926556

3

100

Enter the maximum denominator: 
The PI computed is: 3.1215946526 

Hints

      int maxDenominator;  // to be input
      double sum = 0.0;
      ......

      for (int denominator = 1; denominator <= maxDenominator; denominator += 2) {
         // denominator = 1, 3, 5, 7, ..., maxDenominator
         if (denominator % 4 == 1) {
            // add into sum
            ......
         } else if (denominator % 4 == 3) {
            // subtract from sum
            ......
         } else {
            System.out.println("impossible - error in logic");
         }
      }

Sum of Digits of an Integer (SumOfDigitsInt.java) (Loop & Modulus/Division)

Write a program that prompts user for a positive integer. The program shall read the input as int; compute and print the sum of all its digits. No input validation is needed.

Test Cases

1

12345

Enter a positive integer: 
The sum of all digits is: 15

2

67890

Enter a positive integer: 
The sum of all digits is: 30

3

1

Enter a positive integer: 
The sum of all digits is: 1 

Hints

      // Declare variables
      int inNumber;   // to be input
      int inDigit;    // each digit
      int sum = 0;
      ......

      // Prompt and read inputs as "int"
      ......

      // Extract the "last" digit repeatedly using a while-loop with modulus/divide operations
      while (inNumber > 0) {
         inDigit = inNumber % 10; // extract the "last" digit
         inNumber /= 10;          // drop "last" digit
         sum = ......
      }
      ......

Reverse of an Integer (ReverseInt.java) (Loop & Modulus/Division)

Write a program that prompts user for a positive integer. The program shall read the input as int; and print the reverse of the input integer. No input validation needed.

Test Cases

1

12345

Enter a positive integer: 
The reverse is: 54321

2

67890

Enter a positive integer: 
The reverse is: 09876

3

1

Enter a positive integer: 
The reverse is: 1

Hints

      // Declare variables
      int inNumber;   // to be input
      int inDigit;    // each digit
      ......

      // Extract and drop the "last" digit repeatedly using a while-loop with modulus/divide operations
      while (inNumber > 0) {
         inDigit = inNumber % 10; // extract the "last" digit
         // Print this digit (which is extracted in reverse order)
         ......
         inNumber /= 10;          // drop "last" digit and repeat
      }
      ......

Input Validation (InputValidation.java) (loop & boolean flag)

Your program often needs to validate the user's inputs, e.g., marks shall be between 0 and 100.

Write a program that prompts user for an integer between 0-10 or 90-100. The program shall read the input as an int; and repeat until the user enters a valid input.

Test Cases

1

-1
50
101
95

Enter a number between 0-10 or 90-100: 
Invalid input, try again...
Enter a number between 0-10 or 90-100: 
Invalid input, try again...
Enter a number between 0-10 or 90-100: 
Invalid input, try again...
Enter a number between 0-10 or 90-100: 
You have entered: 95

2

-1
0

Enter a number between 0-10 or 90-100: 
Invalid input, try again...
Enter a number between 0-10 or 90-100: 
You have entered: 0

3

5

Enter a number between 0-10 or 90-100: 
You have entered: 5 

Hints

      // Declare variables
      int numberIn;      // to be input
      boolean isValid;   // boolean flag to control the loop
      ......

      // Use a do-while loop controlled by a boolean flag
      // to repeatably read the input until a valid input is entered
      isValid = false;   // default assuming input is not valid
      do {
         // Prompt and read input
         ......

         // Validate input by setting the boolean flag accordingly
         if (numberIn ......) {
            isValid = true;   // exit the loop
         } else {
            System.out.println(......);  // Print error message and repeat
         }
      } while (!isValid);
      ......

Average with Input Validation (AverageWithInputValidation.java) (Loop & boolean flag)

Write a program that prompts user for the mark (between 0-100 as int) of 3 students; computes the average (in double); and prints the result rounded to 2 decimal places. Your program needs to perform input validation.

Test Cases

1

35
87
99

Enter the mark (0-100) for student 1: 
Enter the mark (0-100) for student 2: 
Enter the mark (0-100) for student 3: 
The average is: 73.67

2

56
101
-1
99
45

Enter the mark (0-100) for student 1: 
Enter the mark (0-100) for student 2: 
Invalid input, try again...
Enter the mark (0-100) for student 2: 
Invalid input, try again...
Enter the mark (0-100) for student 2: 
Enter the mark (0-100) for student 3: 
The average is: 66.67

3

101
100
-1
0
50

Enter the mark (0-100) for student 1: 
Invalid input, try again...
Enter the mark (0-100) for student 1: 
Enter the mark (0-100) for student 2: 
Invalid input, try again...
Enter the mark (0-100) for student 2: 
Enter the mark (0-100) for student 3: 
The average is: 50.00 

Hints

      // Declare constant
      final int NUM_STUDENTS = 3;

      // Declare variables
      int numberIn;
      boolean isValid;   // boolean flag to control the input validation loop
      int sum = 0;
      double average;
      ......

      for (int studentNo = 1; studentNo <= NUM_STUDENTS; ++studentNo) {
          // Prompt user for mark with input validation
          ......
          isValid = false;   // reset for each student assuming input is not valid
          do {
             ......
             // If input is valid, eet isValid = true to exit the loop
             // Else, print error message and repeat
             ......
          } while (!isValid);

          sum += ......;
      }
      ......

Nested-Loops

Checker Pattern (Nested-Loops)

Write a program that prompts user for the size of the pattern (in int); and prints the checker pattern as shown in the sample output.

Test Cases

1

5

Enter the size: 
# # # # # 
 # # # # # 
# # # # # 
 # # # # # 
# # # # # 

2

3

Enter the size: 
# # # 
 # # # 
# # # 

3

1

Enter the size: 
#  

Hints

      // Outer loop to print ALL the rows
      for (int row = 1; row <= size; row++) {
         // Use print() to print a space, if needed, before printing this row
         ......
         // Inner loop to print ALL the columns of ONE row
         for (int col = 1; col <= size; col++) {
            // Use print() here
            ......
         }
         // Print a newline after all the columns
         System.out.println();
      }

Triangular Pattern (A) (Nested-Loops)

Write a program that prompts user for the size of the pattern; and prints the triangular pattern as shown in the sample output.

Test Cases

1

5

Enter the size: 
*
**
***
****
*****

2

4

Enter the size: 
*
**
***
****

3

1

Enter the size: 
* 

Hints

      for (int row = 1; row <= size; row++) {
         for (int col = 1; col <= size; col++) {
            // if (row >= col) print *
            ......
         }
         // Print a newline after all the columns
         ......
      }

Triangular Pattern (C) (Nested-Loops)

Write a program that prompts user for the size of the pattern; and prints the triangular pattern as shown in the sample output.

Test Cases

1

5

Enter the size: 
*****
 ****
  ***
   **
    *

2

4

Enter the size: 
****
 ***
  **
   *

3

1

Enter the size: 
* 

Hints

      for (int row = 1; row <= size; row++) {
         for (int col = 1; col <= size; col++) {
            // if (row <= col) print *
            // else print a space (needed to push the * to the right)
            ......
         }
         // Print a newline after all the columns
         ......
      }

Z Pattern (Nested-Loops)

Write a program that prompts user for the size of the pattern; and print the Z-pattern as shown in the sample output.

Test Cases

1

5

Enter the size: 
*****
   * 
  *  
 *   
*****

2

3

Enter the size: 
***
 * 
***

3

1

Enter the size: 
* 

Hints

The formula for the diagonal is row + col = size + 1, with row and col begin from 1.

The algorithm is:

if row is 1, or row is n, or row + col = n + 1, print *
else print a space

Box with Cross (Nested-Loops)

Write a program that prompts user for the size of the pattern; and prints the box-with-cross pattern as shown in the sample output.

Test Cases

1

8

Enter the size: 
********
*+    +*
* +  + *
*  ++  *
*  ++  *
* +  + *
*+    +*
********

2

7

Enter the size: 
*******
*+   +*
* + + *
*  +  *
* + + *
*+   +*
*******

3

1

Enter the size: 
* 

Hints

The formula for the main diagonal is row = col; while the opposite diagonal is row + col = n + 1, where row and col begin from 1.

The algorithm is:

if row is 1, or row is n, or col is 1, or col is n, print *
else if row = col, or row + col = n + 1, print +
else print a space

Triangular Number Pattern (Nested-Loops)

Write a program that prompts user for the size of the pattern; and prints the triangular number pattern as shown in the sample output.

Test Cases

1

7

Enter the size: 
1234567
 123456
  12345
   1234
    123
     12
      1

2

5

Enter the size: 
12345
 1234
  123
   12
    1

3

1

Enter the size: 
1 

Multiplication Table (Nested-Loops)

Write a program that prompts user for the size; and prints the multiplication table of that size.

Test Cases

1

9

Enter the size of the table: 
 * |   1   2   3   4   5   6   7   8   9
===+====================================
 1 |   1   2   3   4   5   6   7   8   9
 2 |   2   4   6   8  10  12  14  16  18
 3 |   3   6   9  12  15  18  21  24  27
 4 |   4   8  12  16  20  24  28  32  36
 5 |   5  10  15  20  25  30  35  40  45
 6 |   6  12  18  24  30  36  42  48  54
 7 |   7  14  21  28  35  42  49  56  63
 8 |   8  16  24  32  40  48  56  64  72
 9 |   9  18  27  36  45  54  63  72  81

2

5

Enter the size of the table: 
 * |   1   2   3   4   5
===+====================
 1 |   1   2   3   4   5
 2 |   2   4   6   8  10
 3 |   3   6   9  12  15
 4 |   4   8  12  16  20
 5 |   5  10  15  20  25

3

1

Enter the size of the table: 
 * |   1
===+====
 1 |   1 

Hill Pattern (Nested-Loops)

Write a program that prompts user for the number of rows; and prints the Hill pattern as shown in the sample output.

Test Cases

1

5	 

Enter the rows:  
    ^     
   ^^^    
  ^^^^^   
 ^^^^^^^  
^^^^^^^^^ 

2

4 

Enter the rows:  
   ^    
  ^^^   
 ^^^^^  
^^^^^^^ 

3

3 

Enter the rows:  
  ^   
 ^^^  
^^^^^ 

Hints

      for (int row = 1; ......) {
         // numCol = 2*numRows - 1
         for (int col = 1; ......) {
            if ((row + col >= numRows + 1) && (row >= col - numRows + 1)) {
               ......;
            } else {
               ......;
            }
         }
         ......;
      }

or, use 2 sequential inner loops to print the columns:

      for (int row = 1; row <= rows; row++) {
         for (int col = 1; col <= rows; col++) {
            if ((row + col >= rows + 1)) {
               ......
            } else {
               ......
            }
         }
         for (int col = 2; col <= rows; col++) {  // skip col = 1
            if (row >= col) {
               ......
            } else {
               ......
            }
         }
         ......
      }

String and char Operations

Reverse String (String & char)

Write a program that prompts user for a string; and prints the string in the reverse order.

Test Cases

1

abcdefg

Enter a String: 
The reverse is: gfedcba

2

12345

Enter a String: 
The reverse is: 54321

3

a

Enter a String: 
The reverse is: a 

Hints

1. For a String called inStr, you can use inStr.length() to get the length of the String; and inStr.charAt(index) to retrieve the char at the index position, where index begins with 0.
2. Use a for-loop to extract each char of the input String in the reverse order, and print the extracted char. There is no need to save the result.

         String inStr;   // input String
         int inStrLen;   // length of the input String
         ......
   
         System.out.print("Enter a String: ");
         inStr = in.next();   // use next() to read a String
         inStrLen = inStr.length();
   
         // Use inStr.charAt(index) in a loop to extract character at "index" from inStr.
         // The String's index begins at 0 from the left.
         ......
         for (int charIdx = inStrLen - 1; charIdx >= 0; --charIdx) {  // Process the String from the right
            // Print the inStr.charAt(charIdx)
            ......
         }

Phone Keypad (String & char)

On your phone's keypad, the alphabets are mapped to digits as follows: ABC(2), DEF(3), GHI(4), JKL(5), MNO(6), PQRS(7), TUV(8), WXYZ(9).

Write a program called PhoneKeyPad which prompts user for a String (case insensitive), and converts to a sequence of keypad digits.

You are required to use a "switch-case" statement in this exercise.

Test Cases

1

1800flower

Enter a String: 
The phone number is: 1800356937

2

HelloWorld

Enter a String: 
The phone number is: 4355696753 

Hints

1. You could use in.next().toLowerCase() to read an input String and convert it into lowercase to reduce the number of cases.
2. In switch-case, you can handle multiple cases as follows:

         // Declare variables
         String inStr;   // input String
         int inStrLen;   // length of the input String
         char inChar;    // each individual char in the string
         ......
   
         for (int inCharIdx = 0; inCharIdx < inStrLength; ++inCharIdx) {
            inChar = inStr.charAt(inCharIdx);
            switch (inChar) {
               case 'a': case 'b': case 'c':   // same as: if (inChar == 'a' || inChar == 'b' || inChar == 'c')
                  System.out.print(2); break;
               case 'd': case 'e': case 'f':
                  ......
                  ......
               default:
                  System.out.println("error in input");
            }
         }

Count Vowels and Digits (String & char)

Write a program that prompts user for a string and counts the number of vowels (a, e, i, o, u, A, E, I, O, U) and digits (0-9) contained in the string. The program shall print the counts and the percentages (rounded to 2 decimal places).

You are required to use a "nested-if" statement in this exercise.

Test Cases

1

testing12345

Enter a String: 
Number of vowels is: 2 (16.67%)
Number of digits is: 5 (41.67%)

2

1string2strings3strings

Enter a String: 
Number of vowels is: 3 (13.04%)
Number of digits is: 3 (13.04%)

3

bcdfghjklmn

Enter a String: 
Number of vowels is: 0 (0.00%)
Number of digits is: 0 (0.00%) 

Hints

1. Use in.next().toLowerCase() to read an input string and convert it into lowercase to reduce the number of cases.
2. To check if a char c is a digit, you can use boolean expression (c >= '0' && c <= '9'); or use built-in boolean function Character.isDigit(c).
3. To print a % using printf(), you need to use %%. This is because % has a special meaning inside printf(), e.g., %d and %f.

Sum of Digits in String (String, char & int)

Write a program that prompts user for a string. The program shall compute and print the sum of all the digits ('0' to '9') found in the string. Ignore all the non-digit characters.

Test Cases

1

testing12345

Enter a String: 
The sum of all digits is: 15

2

1800flower

Enter a String: 
The sum of all digits is: 9

3

1_2-3@4xyz

Enter a String: 
The sum of all digits is: 10

4

helloworld

Enter a String: 
The sum of all digits is: 0 

Hints

To check if a char c is a digit character '0' to '9', you can use either:

1. boolean expression (c >= '0' && c <= '9'); or
2. built-in boolean function Character.isDigit(c) which returns true if c is a digit.

Take note that char '0' is represented as code number 48, ..., char '5' as 53. To convert char '5' to int 5, subtract it by char '0' (which is int 48).

In other words, to convert a char c to an int i (e.g., '0' to 0, ..., '5' to 5 - which is needed to be added into the sum), use i = c - '0'.

Caesar's Code (String, char & int)

Caesar's code is one of the simplest encryption techniques. Each letter in the plaintext is replaced by a letter some fixed number of position (n) down the alphabet cyclically. In this exercise, we shall pick n=3. That is, 'A' is replaced by 'D', 'B' by 'E', 'C' by 'F', ..., 'X' by 'A', ..., 'Z' by 'C'.

Write a program to cipher the caesar's code. The program shall prompt user for a plaintext string consisting of letters only; compute the ciphertext; and print the ciphertext in uppercase. No input validation needed.

Test Cases

1

testing

Enter a plaintext string: 
The ciphertext string is: WHVWLQJ

2

HELLOWORLD

Enter a plaintext string: 
The ciphertext string is: KHOORZRUOG

3

ASecretText

Enter a plaintext string: 
The ciphertext string is: DVHFUHWWHAW

4

AaBbCcXxYyZz

Enter a plaintext string: 
The ciphertext string is: DDEEFFAABBCC

5

ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz

Enter a plaintext string: 
The ciphertext string is: DEFGHIJKLMNOPQRSTUVWXYZABCDEFGHIJKLMNOPQRSTUVWXYZABC 

Hints

1. Use in.next().toUpperCase() to read an input string and convert it into uppercase to reduce the number of cases.
2. You can use a big nested-if with 26 cases ('A'-'Z'). But it is much better to consider 'A' to 'W' as one case; 'X', 'Y' and 'Z' as 3 separate cases.
3. Take note that char 'A' is represented as code number 65 and char 'D' as 68. However, 'A' + 3 gives 68. This is because char + int is implicitly casted to int + int which returns an int value. To obtain a char value, you need to perform explicit type casting using (char)('A' + 3). Try printing ('A' + 3) with and without type casting.

An Exchange Cipher (String, char & int)

This simple cipher exchanges 'A' and 'Z', 'B' and 'Y', 'C' and 'X', and so on.

Write a program that prompts user for a plaintext string consisting of letters only. You program shall compute the ciphertext; and print the ciphertext in uppercase. No input validation needed.

Test Cases

1

abcXYZ

Enter a plaintext string: 
The ciphertext string is: ZYXCBA

2

testing

Enter a plaintext string: 
The ciphertext string is: GVHGRMT

3

ASecretText

Enter a plaintext string: 
The ciphertext string is: ZHVXIVGGVCG

4

m

Enter a plaintext string: 
The ciphertext string is: N 

Hints

1. Use in.next().toUpperCase() to read an input string and convert it into uppercase to reduce the number of cases.
2. You can use a big nested-if with 26 cases ('A'-'Z'); or use the following relationship:

   'A' + 'Z' == 'B' + 'Y' == 'C' + 'X' == ... == plainTextChar + cipherTextChar
   Hence, cipherTextChar = 'A' + 'Z' - plainTextChar

Bin2Dec (a) (String/char & Number Conversion)

Write a program to convert a binary string to its decimal equivalent. The program shall prompt user for a binary number; read the input as String; compute and print its decimal equivalent. No input validation is needed.

Test Cases

1

1011

Enter a binary string: 
The decimal equivalent is: 11

2

10000011

Enter a binary string: 
The decimal equivalent is: 131

3

0

Enter a binary string: 
The decimal equivalent is: 0

4

1

Enter a binary string: 
The decimal equivalent is: 1 

Oct2Dec (String/char & Number Conversion)

Write a program to convert a octal (base 8) string to its decimal equivalent. The program shall prompt user for a octal number; read the input as String; compute and print its decimal equivalent. No input validation is needed.

Test Cases

1

12

Enter an octal string: 
The decimal equivalent is: 10

2

7123

Enter an octal string: 
The decimal equivalent is: 3667

3

0

Enter an octal string: 
The decimal equivalent is: 0

Palindromic Word (String/char & Two Loop Indexes)

A word that reads the same backward as forward is called a palindrome, e.g., "mom", "dad", "racecar", "madam", and "Radar" (case-insensitive). Write a program called PalindromicWordTest, that prompts user for a word and decides if the input word is a palindrome.

Test Cases

1

Radar

Enter a String: 
"Radar" is palindromic

2

RaceCar

Enter a String: 
"RaceCar" is palindromic

3

m

Enter a String: 
"m" is palindromic

4

Hello

Enter a String: 
"Hello" is not palindromic 

Hints

      // Declare variables
      String inStr;           // The input string, need to save for output printing
      String inStrLowerCase;  // The input string in lowercase to reduce the cases in comparison
      int inStrLen;           // The length of the input string
      char forwardChar, backwardChar;   // to compare these two chars, scan forward and backward
      boolean isPalindromic;  // boolean flag
      ......

      isPalindromic = true;     // assume it is true, unless our check fails
      for (int forwardIdx = 0, backwardIdx = inStrLen - 1; forwardIdx < inStrLen/2; ++forwardIdx, --backwardIdx) {
         forwardChar = ......;
         backwardChar = ......;
         if (forwardChar != backwardChar) {
            isPalindromic = false;
            break;    // upon the first encounter, no need to go further
         }
      }
      ......

Arrays

Print Array (Array & Loop)

Write a program which prompts user for the number of items in an array (a non-negative integer), reads it, and saves it in an int variable called numItems. It then prompts user for the values of all the items and saves them in an int array called items. The program shall then print the contents of the array in the form of [x1, x2, ..., xn]. No input validation is needed.

Test Cases

1

5
3 2 5 6 9

Enter the number of items: 
Enter the value of all items (separated by space): 
The values are: [3, 2, 5, 6, 9]

2

2
88 99

Enter the number of items: 
Enter the value of all items (separated by space): 
The values are: [88, 99]

3

1
99

Enter the number of items: 
Enter the value of all items (separated by space): 
The values are: [99]

4

0

Enter the number of items: 
The values are: [] 

Hints

      // Declare variables
      int numItems;
      int[] items;  // Declare array name, to be allocated after numItems is known
      ......

      // Prompt for a non-negative integer for the number of items;
      // and read the input as "int". No input validation.
      ......

      // Allocate the array
      items = new int[numItems];

      // Prompt and read the items into the "int" array, if array length > 0
      if (items.length > 0) {
         ......
         for (int i = 0; i < items.length; ++i) {
            ......
         }
      }

      // Print array contents, need to handle first item and subsequent items differently
      ......
      for (int i = 0; i < items.length; ++i) {
         if (i == 0) {
            // Print the first item without a leading commas
            ......
         } else {
            // Print the subsequent items with a leading commas
            ......
         }
         // or, using a one liner
         //System.out.print((i == 0) ? ...... : ......);
      }
      ......

Print Array in Stars (Array & Loop)

Write a program which prompts user for the number of items in an array (a non-negative integer), reads it, and saves it in an int variable called numItems. It then prompts user for the values of all the items (non-negative integers) and saves them in an int array called items.

The program shall then print the contents of the array in a graphical form, with the array index and values represented by number of stars. No input validation is needed.

Test Cases

1

5	 
7 4 3 0 7 

Enter the number of items:  
Enter the value of all items (separated by space):  
0: *******(7) 
1: ****(4) 
2: ***(3) 
3: (0) 
4: *******(7) 

2

2 
8 4 

Enter the number of items:  
Enter the value of all items (separated by space):  
0: ********(8) 
1: ****(4) 

3

1 
9 

Enter the number of items:  
Enter the value of all items (separated by space):  
0: *********(9) 

4

0 

Enter the number of items:  

Hints

      // Declare variables
      int numItems;
      int[] items;  // Declare array name, to be allocated after numItems is known
      ......
      ......

      // Print array contents (in index: number of stars) using a nested-loop
      for (int idx = 0; idx < items.length; ++idx) {  // row
         System.out.print(idx + ": ");
         // Print value as the number of stars
         for (int starNo = 1; starNo <= items[idx]; ++starNo) {  // col
            System.out.print("*");
         }
         ......
      }
      ......

Grades Statistics (Array & Loop)

Write a program which prompts user for the number of students in a class (a non-negative integer), reads it, and saves it in an int variable called numStudents. It then prompts user for the grade of each of the students (integer between 0 to 100) and saves them in an int array called grades. The program shall then compute and print the average (in double rounded to 2 decimal places) and minimum/maximum (in int). No input validation is needed.

Test Cases

1

3
90
85
78

Enter the number of students: 
Enter the grade for student 1: 
Enter the grade for student 2: 
Enter the grade for student 3: 
The average is: 84.33
The minimum is: 78
The maximum is: 90

2

5
98
78
78
87
76

Enter the number of students: 
Enter the grade for student 1: 
Enter the grade for student 2: 
Enter the grade for student 3: 
Enter the grade for student 4: 
Enter the grade for student 5: 
The average is: 83.40
The minimum is: 76
The maximum is: 98

3

1
50

Enter the number of students: 
Enter the grade for student 1: 
The average is: 50.00
The minimum is: 50
The maximum is: 50

Grades Histogram Bins (Arrays)

Write a program that prompts user for the number of students in a class (a non-negative integer), reads it, and saves it in an int variable called numStudents. It then prompts user for the grade of each of the students (integer between 0 to 100) and saves them in an int array called grades.

Assume that the grades are between 0 and 100. The program shall then create 10 histogram bins to contain the counts of grades between 0-9, 10-19, ..., 90-100, respectively, in an int array called bins; and print the contents of the bins as shown in the sample output. No input validation is needed.

Test Cases

1

7
90
100
89
86
0
5
50

Enter the number of students: 
Enter the grade for student 1: 
Enter the grade for student 2: 
Enter the grade for student 3: 
Enter the grade for student 4: 
Enter the grade for student 5: 
Enter the grade for student 6: 
Enter the grade for student 7: 
 0-  9: 2
10- 19: 0
20- 29: 0
30- 39: 0
40- 49: 0
50- 59: 1
60- 69: 0
70- 79: 0
80- 89: 2
90-100: 2

2

8
88
45
89
45
100
0
98
90

Enter the number of students: 
Enter the grade for student 1: 
Enter the grade for student 2: 
Enter the grade for student 3: 
Enter the grade for student 4: 
Enter the grade for student 5: 
Enter the grade for student 6: 
Enter the grade for student 7: 
Enter the grade for student 8: 
 0-  9: 1
10- 19: 0
20- 29: 0
30- 39: 0
40- 49: 2
50- 59: 0
60- 69: 0
70- 79: 0
80- 89: 2
90-100: 3

3

1
100

Enter the number of students: 
Enter the grade for student 1: 
 0-  9: 0
10- 19: 0
20- 29: 0
30- 39: 0
40- 49: 0
50- 59: 0
60- 69: 0
70- 79: 0
80- 89: 0
90-100: 1

4

0

Enter the number of students: 
 0-  9: 0
10- 19: 0
20- 29: 0
30- 39: 0
40- 49: 0
50- 59: 0
60- 69: 0
70- 79: 0
80- 89: 0
90-100: 0 

Hints

      // Declare variables
      int numStudents;
      int[] grades;     // Declare array name, to be allocated after numStudents is known
      int[] bins = new int[10];   // int array of 10 histogram bins for 0-9, 10-19, ..., 90-100

      ......

      // Populate the bins
      for (int i = 0; i < grades.length; ++i) {
         if (grades[i] == 100) {   // Need to handle 90-100 separately as it has 11 items.
            ++bins[9];
         } else {
            ++bins[grades[i]/10];
         }
      }

      // Print the bins
      for (int binIdx = 0; binIdx < bins.length; ++binIdx) {
         if (binIdx != 9) {   // Need to handle 90-100 separately as it has 11 items.
            System.out.printf("%2d-%3d: ", binIdx*10, ....);
         } else {
            System.out.print(......);
         }
         System.out.println(bins[binIdx]);
      }

Grades Histogram Horizontal (Array)

Write a program that prompts user for the number of students in a class (a non-negative integer), reads it, and saves it in an int variable called numStudents. It then prompts user for the grade of each of the students (integer between 0 to 100) and saves them in an int array called grades.

Assume that the grades are between 0 and 100. The program shall then create 10 histogram bins to contain the counts of grades between 0-9, 10-19, ..., 90-100, respectively, in an int array called bins; and print the histogram horizontally as shown in the sample output. No input validation is needed.

Test Cases

1

7
90
100
89
86
0
5
50

Enter the number of students: 
Enter the grade for student 1: 
Enter the grade for student 2: 
Enter the grade for student 3: 
Enter the grade for student 4: 
Enter the grade for student 5: 
Enter the grade for student 6: 
Enter the grade for student 7: 
 0-  9: **
10- 19: 
20- 29: 
30- 39: 
40- 49: 
50- 59: *
60- 69: 
70- 79: 
80- 89: **
90-100: **

2

8
88
45
89
45
100
0
98
90

Enter the number of students: 
Enter the grade for student 1: 
Enter the grade for student 2: 
Enter the grade for student 3: 
Enter the grade for student 4: 
Enter the grade for student 5: 
Enter the grade for student 6: 
Enter the grade for student 7: 
Enter the grade for student 8: 
 0-  9: *
10- 19: 
20- 29: 
30- 39: 
40- 49: **
50- 59: 
60- 69: 
70- 79: 
80- 89: **
90-100: ***

3

1
100

Enter the number of students: 
Enter the grade for student 1: 
 0-  9: 
10- 19: 
20- 29: 
30- 39: 
40- 49: 
50- 59: 
60- 69: 
70- 79: 
80- 89: 
90-100: *

4

0

Enter the number of students: 
 0-  9: 
10- 19: 
20- 29: 
30- 39: 
40- 49: 
50- 59: 
60- 69: 
70- 79: 
80- 89: 
90-100: 

Grades Histogram Vertical (Array)

Write a program that prompts user for the number of students in a class (a non-negative integer), reads it, and saves it in an int variable called numStudents. It then prompts user for the grade of each of the students (integer between 0 to 100) and saves them in an int array called grades.

Assume that the grades are between 0 and 100. The program shall then create 10 histogram bins to contain the counts of grades between 0-9, 10-19, ..., 90-100, respectively, in an int array called bins; and print the histogram vertically as shown in the sample output. No input validation is needed.

Test Cases

1

7
90
100
89
86
0
5
50

Enter the number of students: 
Enter the grade for student 1: 
Enter the grade for student 2: 
Enter the grade for student 3: 
Enter the grade for student 4: 
Enter the grade for student 5: 
Enter the grade for student 6: 
Enter the grade for student 7: 
   *                                                       *      *   
   *                                  *                    *      *   
  0-9   10-19  20-29  30-39  40-49  50-59  60-69  70-79  80-89  90-100

2

8
88
45
89
45
100
0
98
90

Enter the number of students: 
Enter the grade for student 1: 
Enter the grade for student 2: 
Enter the grade for student 3: 
Enter the grade for student 4: 
Enter the grade for student 5: 
Enter the grade for student 6: 
Enter the grade for student 7: 
Enter the grade for student 8: 
                                                                  *   
                               *                           *      *   
   *                           *                           *      *   
  0-9   10-19  20-29  30-39  40-49  50-59  60-69  70-79  80-89  90-100

3

1
100

Enter the number of students: 
Enter the grade for student 1: 
                                                                  *   
  0-9   10-19  20-29  30-39  40-49  50-59  60-69  70-79  80-89  90-100

4

0

Enter the number of students: 
  0-9   10-19  20-29  30-39  40-49  50-59  60-69  70-79  80-89  90-100

Methods

Odd or Even (Method)

Write a boolean method called isOdd(int number) that returns true if the given int number is an odd number. The signature of the method is:

  public static boolean isOdd(int number)

Also write the main() method that prompts user for an int number, and prints the result.

Test Cases

1

9

Enter a number: 
9 is an odd number

2

-9

Enter a number: 
-9 is an odd number

3

0

Enter a number: 
0 is an even number 

Magic Number (Method)

Write a boolean method called isMagic(int number) that returns true if the given number (a positive int) contains the digit 8, e.g., 18, 82, 1688. The signature of the method is:

  public static boolean isMagic(int number);

Also write the main() method that prompts user for a number, and prints the result.

Test Cases

1

18

Enter a positive integer: 	
18 is a magic number

2

7654321

Enter a positive integer: 
7654321 is not a magic number

3

8

Enter a positive integer: 
8 is a magic number

4

1

Enter a positive integer: 
1 is not a magic number

5

168899

Enter a positive integer: 
168899 is a magic number 

Hints

You could either convert the int to a String and check each individual char; or use modulus-divide-10 to extract each individual digit of the int.

int array methods (Array & Method)

Write the following methods that take an int array as its argument:

   public static void print(int[] array);      // print [x1, x2, ..., xn]
   public static int min(int[] array);         // Returns the minimum
   public static int max(int[] array);         // Returns the maximum
   public static int sum(int[] array);         // Returns the sum
   public static double average(int[] array);  // Returns the average in double
   public static boolean isEmpty(int[] array); // Returns true if array's length is 0

Also write the main() method that prompts user for the size of an int array, followed by the values; and calls these methods as shown in the sample output.

Test Cases

1

5
8 6 1 8 5

Enter the number of items: 
Enter the value of all items (separated by space): 
The values are: [8, 6, 1, 8, 5]
The min is: 1
The max is: 8
The sum is: 28
The average (rounded to 2 decimal places) is: 5.60
This array is not empty

2

3
87 54 61

Enter the number of items: 
Enter the value of all items (separated by space): 
The values are: [87, 54, 61]
The min is: 54
The max is: 87
The sum is: 202
The average (rounded to 2 decimal places) is: 67.33
This array is not empty

3

1
55

Enter the number of items: 
Enter the value of all items (separated by space): 
The values are: [55]
The min is: 55
The max is: 55
The sum is: 55
The average (rounded to 2 decimal places) is: 55.00
This array is not empty 

Search an Array (Array & Method)

Write a method called search(), which takes an array of int and an int; and returns the array index if the array contains the given int; or -1 otherwise. The method's signature is as follows:

public static int search(int[] array, int key);

Also write the main() method that prompts user for the size of an int array, followed by its values and a search key; and calls the method as shown in the sample output.

Test Cases

1

5
6 1 8 2 4
8

Enter the number of items: 
Enter the value of all items (separated by space): 
Enter the search key: 
8 is found with index 2

2

4
8 2 6 1
9

Enter the number of items: 
Enter the value of all items (separated by space): 
Enter the search key: 
9 is not found

3

1
9
8

Enter the number of items: 
Enter the value of all items (separated by space): 
Enter the search key: 
8 is not found

4

0
9

Enter the number of items: 
Enter the search key: 
9 is not found 

Reverse an Array (Array & Method)

Write a method called reverse(int[] array) to reverse the contents of the given array; and a method called print(int[] array) to print the array. The signatures are:

  public static void reverse(int[] array);  // Reverse the contents of the given int array, in place
  public static void print(int[] array);    // Print  [x1, x2, ..., xN]

Also write the main() method that prompts user for the size of an int array, followed by the values; and calls these methods as shown in the sample output.

Test Cases

1

5
1 2 3 4 5

Enter the number of items: 
Enter the value of all items (separated by space): 
The original array is: [1, 2, 3, 4, 5]
The reverse is: [5, 4, 3, 2, 1]

2

3
87 54 61

Enter the number of items: 
Enter the value of all items (separated by space): 
The original array is: [87, 54, 61]
The reverse is: [61, 54, 87]

3

1
55

Enter the number of items: 
Enter the value of all items (separated by space): 
The original array is: [55]
The reverse is: [55]

4

0

Enter the number of items: 
The original array is: []
The reverse is: [] 

Latest version tested: JDK 15.0.2
Last modified: March 2021