If statement in Java - Mini Project: Build & Apply

If Statement Basics in Java

📖 Scenario: You are creating a simple program that checks if a person is old enough to vote. Voting age is 18 years or older.

🎯 Goal: Build a Java program that uses an if statement to check a person's age and print whether they can vote or not.

📋 What You'll Learn

Create an integer variable age with the exact value 20

Create an integer variable votingAge and set it to 18

Use an if statement to check if age is greater than or equal to votingAge

Print "You can vote!" if the condition is true

Print "You cannot vote yet." if the condition is false

💡 Why This Matters

🌍 Real World

Checking age eligibility is common in many apps, like voting, driving, or buying age-restricted items.

💼 Career

Understanding if statements is essential for decision-making in programming jobs.

1

Create the age variable

Create an integer variable called age and set it to 20.

Java

// Your code here

Hint

Use int age = 20; inside the main method.

2

Add the votingAge variable

Add an integer variable called votingAge and set it to 18 inside the main method, below age.

Java

public class Main {
    public static void main(String[] args) {
        int age = 20;
        // Your code here
    }
}

Hint

Declare int votingAge = 18; after age.

3

Write the if statement

Write an if statement that checks if age is greater than or equal to votingAge. Inside the if block, write System.out.println("You can vote!");. Add an else block that prints "You cannot vote yet.".

Java

public class Main {
    public static void main(String[] args) {
        int age = 20;
        int votingAge = 18;
        // Your code here
    }
}

Hint

Use if (age >= votingAge) { ... } else { ... } structure.

4

Print the result

Run the program and observe the output. It should print You can vote!.

Java

public class Main {
    public static void main(String[] args) {
        int age = 20;
        int votingAge = 18;
        if (age >= votingAge) {
            System.out.println("You can vote!");
        } else {
            System.out.println("You cannot vote yet.");
        }
    }
}
// Run the program to see the output

Hint

Make sure to run the program and check the console output.

Practice

1. What does an if statement do in Java?

easy

A. It stores data in a variable.

B. It repeats code multiple times.

C. It creates a new class.

D. It runs code only if a condition is true.

Solution

1. Step 1: Understand the purpose of an if statement

   An if statement checks a condition and decides whether to run some code based on that condition.

2. Step 2: Match the description to the options

   It runs code only if a condition is true. correctly says it runs code only if the condition is true, which matches the if statement's behavior.

3. Final Answer:

   It runs code only if a condition is true. -> Option D

4. Quick Check:

   If statement = runs code if true [OK]

Hint: If checks true condition to run code [OK]

Common Mistakes:

• Confusing if with loops
• Thinking if stores data
• Mixing if with class creation

2. Which of these is the correct syntax for an if statement in Java?

easy

A. if (condition) System.out.println("Yes");

B. if condition { System.out.println("Yes"); }

C. if condition: System.out.println("Yes");

D. if (condition) then { System.out.println("Yes"); }

Solution

1. Step 1: Recall Java if statement syntax

   Java requires parentheses around the condition and braces are optional if only one statement follows.

2. Step 2: Check each option

   if (condition) System.out.println("Yes"); uses parentheses and a single statement without braces, which is valid syntax.

3. Final Answer:

   if (condition) System.out.println("Yes"); -> Option A

4. Quick Check:

   Parentheses needed around condition [OK]

Hint: Use parentheses around condition in if [OK]

Common Mistakes:

• Omitting parentheses around condition
• Using colons instead of braces
• Adding 'then' keyword

3. What will be the output of this code?

int x = 10;
if (x > 5) {
  System.out.println("Big number");
} else {
  System.out.println("Small number");
}

medium

A. Small number

B. Big number

C. No output

D. Syntax error

Solution

1. Step 1: Evaluate the condition x > 5

   Since x is 10, the condition 10 > 5 is true.

2. Step 2: Determine which block runs

   The if block runs and prints "Big number" because the condition is true.

3. Final Answer:

   Big number -> Option B

4. Quick Check:

   10 > 5 is true, prints "Big number" [OK]

Hint: Check if condition true to pick output [OK]

Common Mistakes:

• Choosing else output when condition is true
• Thinking no output if condition true
• Confusing syntax with output

4. Find the error in this code:

int num = 7;
if num > 5 {
  System.out.println("Greater");
}

medium

A. Braces not allowed in if

B. Missing semicolon after if

C. Missing parentheses around condition

D. Wrong variable name

Solution

1. Step 1: Check if statement syntax

   Java requires parentheses around the condition in an if statement.

2. Step 2: Identify the missing parentheses

   The code has if num > 5 without parentheses, which causes a syntax error.

3. Final Answer:

   Missing parentheses around condition -> Option C

4. Quick Check:

   If condition must be in parentheses [OK]

Hint: Always put condition in parentheses [OK]

Common Mistakes:

• Forgetting parentheses around condition
• Adding semicolon after if line
• Misnaming variables

5. You want to print "Even" if a number is even and "Odd" if it is odd. Which code correctly uses an if statement to do this?

int n = 4;
// Your code here

hard

A. if (n % 2 == 0) {
System.out.println("Even");
} else {
System.out.println("Odd");
}

B. if (n / 2 == 0) {
System.out.println("Even");
} else {
System.out.println("Odd");
}

C. if (n % 2 = 0) {
System.out.println("Even");
} else {
System.out.println("Odd");
}

D. if (n % 2 != 0) {
System.out.println("Even");
} else {
System.out.println("Odd");
}

Solution

1. Step 1: Understand how to check even numbers

   A number is even if dividing by 2 leaves remainder 0, so use n % 2 == 0.

2. Step 2: Check each option's condition

   if (n % 2 == 0) { System.out.println("Even"); } else { System.out.println("Odd"); } correctly uses n % 2 == 0 to check evenness and prints "Even" or "Odd" accordingly.

3. Final Answer:

   if (n % 2 == 0) { System.out.println("Even"); } else { System.out.println("Odd"); } -> Option A

4. Quick Check:

   Use modulus == 0 for even check [OK]

Hint: Use n % 2 == 0 to check even numbers [OK]

Common Mistakes:

• Using assignment = instead of comparison ==
• Checking division instead of remainder
• Reversing even and odd conditions