If–else statement in Java - Step-by-Step Execution

Concept Flow - If–else statement

Start

↓

Evaluate condition

↓

Execute if-block

↓

End if-block

↓

Execute else-block

↓

End else-block

↓

Continue with rest of program

The program checks a condition. If true, it runs the 'if' part; if false, it runs the 'else' part. Then it continues.

Execution Sample

Java

int x = 10;
if (x > 5) {
    System.out.println("x is greater than 5");
} else {
    System.out.println("x is 5 or less");
}

Checks if x is greater than 5 and prints a message accordingly.

Execution Table

Step	Condition (x > 5)	Result	Branch Taken	Output
1	10 > 5	true	if-block	x is greater than 5
2	End of if–else	-	-	Program continues

💡 Condition true, executed if-block, then program continues

Variable Tracker

Variable	Start	After Condition Check	Final
x	10	10	10

Key Moments - 2 Insights

Why does the program not run the else-block when x is 10?

Because the condition x > 5 is true (see execution_table step 1), so only the if-block runs.

What happens if the condition is false?

The program skips the if-block and runs the else-block instead, as shown in the concept flow.

Visual Quiz - 3 Questions

Look at the execution table, what is the output at step 1?

A "x is greater than 5"

B "x is 5 or less"

C No output

D Error

💡 Hint

Check the 'Output' column in execution_table row 1.

At which step does the program decide which branch to take?

A Step 2

B Before Step 1

C Step 1

D After Step 2

💡 Hint

Look at the 'Condition' and 'Branch Taken' columns in execution_table.

If x was 3 instead of 10, which branch would run?

A if-block

B else-block

C Both if and else blocks

D Neither block

💡 Hint

Refer to the concept_flow and key_moments about condition false case.

Concept Snapshot

if (condition) {
  // code runs if condition true
} else {
  // code runs if condition false
}
Checks condition once, runs one branch only.

Full Transcript

This example shows how an if–else statement works in Java. The program sets x to 10. It checks if x is greater than 5. Since 10 is greater than 5, it runs the code inside the if-block and prints "x is greater than 5". It skips the else-block. Then the program continues. If the condition was false, it would run the else-block instead. This way, the program chooses one path based on the condition.

Practice

1. What does an if-else statement do in Java?

easy

A. It defines a new class.

B. It repeats code multiple times.

C. It stores multiple values in a list.

D. It chooses between two actions based on a condition.

Solution

1. Step 1: Understand the purpose of if-else

   An if-else statement lets the program decide between two paths depending on a condition.

2. Step 2: Compare with other options

   Repeating code is done by loops, storing values is done by collections, and defining classes is unrelated.

3. Final Answer:

   It chooses between two actions based on a condition. -> Option D

4. Quick Check:

   If-else = choose between two paths [OK]

Hint: If you want two choices, use if-else [OK]

Common Mistakes:

• Confusing if-else with loops
• Thinking if-else stores data
• Mixing if-else with class definitions

2. Which of the following is the correct syntax for an if-else statement in Java?

easy

A. if condition { } else { }

B. if (condition) { } else { }

C. if (condition) then { } else { }

D. if condition then { } else { }

Solution

1. Step 1: Recall Java syntax rules

   Java requires parentheses around the condition and curly braces for code blocks.

2. Step 2: Check each option

   Only if (condition) { } else { } uses parentheses and curly braces correctly without extra keywords like 'then'.

3. Final Answer:

   if (condition) { } else { } -> Option B

4. Quick Check:

   Parentheses + braces = correct syntax [OK]

Hint: Remember: condition in () and code in {} [OK]

Common Mistakes:

• Omitting parentheses around condition
• Using 'then' keyword incorrectly
• Missing curly braces for blocks

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

int x = 10;
if (x > 5) {
    System.out.println("Greater");
} else {
    System.out.println("Smaller or equal");
}

medium

A. Greater

B. Smaller or equal

C. No output

D. Compilation 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 "Greater"; the else block is skipped.

3. Final Answer:

   Greater -> Option A

4. Quick Check:

   10 > 5 is true, so print "Greater" [OK]

Hint: Check condition true? Run if-block, else run else-block [OK]

Common Mistakes:

• Confusing > with <
• Thinking else block runs when if is true
• Assuming no output if condition true

4. Identify the error in this Java code snippet:

int num = 7;
if num > 5 {
    System.out.println("Yes");
} else {
    System.out.println("No");
}

medium

A. Missing curly braces around else block.

B. Missing semicolon after if statement.

C. Missing parentheses around the condition in if statement.

D. Variable num is not declared.

Solution

1. Step 1: Check if statement syntax

   Java requires parentheses around the condition in an if statement.

2. Step 2: Verify other parts

   Semicolon after if is not needed; curly braces are present; num is declared.

3. Final Answer:

   Missing parentheses around the condition in if statement. -> Option C

4. Quick Check:

   If condition needs () [OK]

Hint: Always put condition inside () in if [OK]

Common Mistakes:

• Omitting parentheses in if condition
• Adding unnecessary semicolon after if
• Forgetting to declare variables

5. You want to write a Java program that prints "Even" if a number is even, and "Odd" if it is odd. Which if-else code correctly does 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"); } uses correct equality check with == and modulo operator. if (n / 2 == 0) { System.out.println("Even"); } else { System.out.println("Odd"); } uses division instead of modulo. if (n % 2 = 0) { System.out.println("Even"); } else { System.out.println("Odd"); } uses assignment = instead of comparison ==. if (n % 2 != 0) { System.out.println("Even"); } else { System.out.println("Odd"); } reverses logic.

3. Final Answer:

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

4. Quick Check:

   Use modulo == 0 to check even [OK]

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

Common Mistakes:

• Using = instead of == for comparison
• Using division instead of modulo
• Reversing even and odd logic