Relational operators in Java - Mini Project: Build & Apply

Relational Operators in Java

📖 Scenario: You are creating a simple program to compare ages of two friends to see who is older or if they are the same age.

🎯 Goal: Build a Java program that uses relational operators to compare two age values and prints the comparison results.

📋 What You'll Learn

Create two integer variables named ageAlice and ageBob with exact values 25 and 30 respectively.

Create a boolean variable named isAliceOlder that stores the result of comparing if Alice is older than Bob.

Create a boolean variable named isBobOlder that stores the result of comparing if Bob is older than Alice.

Create a boolean variable named areSameAge that stores the result of checking if Alice and Bob have the same age.

Print the values of isAliceOlder, isBobOlder, and areSameAge each on a new line.

💡 Why This Matters

🌍 Real World

Comparing values is common in real life, like checking if someone is old enough to vote or drive.

💼 Career

Understanding relational operators is essential for decision-making in programming, used in conditions and loops.

1

Create age variables

Create two integer variables called ageAlice and ageBob with values 25 and 30 respectively.

Java

// Your code here

Hint

Use int to declare whole number variables and assign the exact values.

2

Create relational boolean variables

Create boolean variables isAliceOlder, isBobOlder, and areSameAge that store the results of ageAlice > ageBob, ageBob > ageAlice, and ageAlice == ageBob respectively.

Java

public class Main {
    public static void main(String[] args) {
        int ageAlice = 25;
        int ageBob = 30;
        // Your code here
    }
}

Hint

Use relational operators > and == to compare the ages and store the results in boolean variables.

3

Print the comparison results

Use System.out.println to print the values of isAliceOlder, isBobOlder, and areSameAge each on a new line.

Java

public class Main {
    public static void main(String[] args) {
        int ageAlice = 25;
        int ageBob = 30;
        boolean isAliceOlder = ageAlice > ageBob;
        boolean isBobOlder = ageBob > ageAlice;
        boolean areSameAge = ageAlice == ageBob;
        // Your code here
    }
}

Hint

Use System.out.println to show each boolean result on its own line.

4

Run and check output

Run the program and confirm the output shows false, true, and false each on a new line.

Java

public class Main {
    public static void main(String[] args) {
        int ageAlice = 25;
        int ageBob = 30;
        boolean isAliceOlder = ageAlice > ageBob;
        boolean isBobOlder = ageBob > ageAlice;
        boolean areSameAge = ageAlice == ageBob;
        System.out.println(isAliceOlder);
        System.out.println(isBobOlder);
        System.out.println(areSameAge);
        // No code needed here
    }
}

Hint

The output should be three lines: false, true, and false.

Practice

1. Which of the following relational operators in Java checks if two values are not equal?

easy

A. ==

B. >=

C. !=

D. <

Solution

1. Step 1: Understand the meaning of relational operators

   Relational operators compare two values and return true or false based on the comparison.

2. Step 2: Identify the operator for 'not equal'

   The operator '!=' means 'not equal to' in Java.

3. Final Answer:

   != -> Option C

4. Quick Check:

   Not equal operator = != [OK]

Hint: Remember: '!=' means not equal in Java [OK]

Common Mistakes:

• Confusing '!=' with '=='
• Using '=' instead of '=='
• Mixing up '<' and '<='

2. Which of the following is the correct syntax to check if variable a is greater than or equal to variable b in Java?

easy

A. a => b

B. a >= b

C. a =< b

D. a =>= b

Solution

1. Step 1: Recall the correct relational operator syntax

   The operator for 'greater than or equal to' is written as '>=' in Java.

2. Step 2: Check each option for correct syntax

   a >= b uses '>=', which is correct. Other options have invalid syntax.

3. Final Answer:

   a >= b -> Option B

4. Quick Check:

   Greater or equal operator = >= [OK]

Hint: Use '>=' for greater or equal, not '=>' or '=<' [OK]

Common Mistakes:

• Writing '=>' instead of '>='
• Using '=' instead of '=='
• Confusing '<=' and '=>'

3. What will be the output of the following Java code?

int x = 5;
int y = 10;
System.out.println(x < y);
System.out.println(x == y);
System.out.println(x != y);

medium

A. false false true

B. false true false

C. true true false

D. true false true

Solution

1. Step 1: Evaluate each relational expression

   x is 5 and y is 10. So, x < y is true, x == y is false, and x != y is true.

2. Step 2: Write the output in order

   The printed output will be: true false true.

3. Final Answer:

   true false true -> Option D

4. Quick Check:

   5 < 10 = true, 5 == 10 = false, 5 != 10 = true [OK]

Hint: Compare values step-by-step to get true/false results [OK]

Common Mistakes:

• Mixing up == and !=
• Assuming x == y is true
• Confusing output order

4. Identify the error in the following Java code snippet:

int a = 7;
int b = 3;
if (a <> b) {
    System.out.println("Not equal");
}

medium

A. The operator '<>' is invalid in Java

B. Missing semicolon after if statement

C. Variables a and b are not declared

D. The print statement syntax is incorrect

Solution

1. Step 1: Check the relational operator used

   The operator '<>' is not a valid relational operator in Java. Java uses '!=' for not equal.

2. Step 2: Verify other syntax elements

   Semicolons and print statement are correct. Variables are declared properly.

3. Final Answer:

   The operator '<>' is invalid in Java -> Option A

4. Quick Check:

   Use '!=' for not equal, not '<>' [OK]

Hint: Use '!=' for not equal; '<>' is invalid in Java [OK]

Common Mistakes:

• Using '<>' instead of '!='
• Forgetting semicolons
• Incorrect print syntax

5. Given the code below, what will be the output?

int a = 4;
int b = 4;
int c = 5;
boolean result = (a <= b) && (c > b);
System.out.println(result);

Choose the correct output.

hard

A. true

B. false

C. Compilation error

D. Runtime exception

Solution

1. Step 1: Evaluate each relational expression

   a <= b is 4 <= 4, which is true. c > b is 5 > 4, which is true.

2. Step 2: Evaluate the logical AND operation

   Both conditions are true, so (true && true) is true.

3. Final Answer:

   true -> Option A

4. Quick Check:

   4 <= 4 and 5 > 4 = true [OK]

Hint: Both conditions must be true for && to be true [OK]

Common Mistakes:

• Confusing && with ||
• Misreading <= as < only
• Assuming false if equal values