Nested if statements in Java - Step-by-Step Execution

Concept Flow - Nested if statements

Start

↓

Check if condition1

|Yes↓

Check if condition2

|Yes↓

Execute inner if block

↓

Else inner if block

↓

Continue after nested if

↓

Else outer if block

↓

End

First, the outer condition is checked. If true, the inner condition is checked next. Depending on inner condition, different blocks run. If outer condition is false, the else block runs.

Execution Sample

Java

int x = 10;
if (x > 5) {
  if (x < 15) {
    System.out.println("x is between 6 and 14");
  }
}

Checks if x is greater than 5, then if x is less than 15, prints a message.

Execution Table

Step	Condition Checked	Condition Result	Branch Taken	Output
1	x > 5	true	Enter outer if
2	x < 15	true	Enter inner if	x is between 6 and 14
3	End of nested if	-	Exit nested if

💡 All conditions checked, nested if blocks executed accordingly.

Variable Tracker

Variable	Start	After Step 1	After Step 2	Final
x	10	10	10	10

Key Moments - 2 Insights

Why does the inner if only run when the outer if is true?

Because the inner if is inside the outer if block, it only executes if the outer condition is true, as shown in execution_table step 1 and 2.

What happens if the outer if condition is false?

The inner if is skipped entirely, and the program moves to the else block or continues after the nested if, as implied by the concept_flow.

Visual Quiz - 3 Questions

Look at the execution_table, what is the result of the condition 'x > 5' at step 1?

A undefined

B false

C true

D null

💡 Hint

Check the 'Condition Result' column in execution_table row 1.

At which step does the program print 'x is between 6 and 14'?

A Step 1

B Step 2

C Step 3

D No output

💡 Hint

Look at the 'Output' column in execution_table row 2.

If x was 4, what would happen to the execution flow?

A Outer if is false, inner if skipped

B Inner if runs

C Both ifs run

D Program crashes

💡 Hint

Refer to concept_flow and key_moments about outer if controlling inner if execution.

Concept Snapshot

Nested if statements check one condition inside another.
Syntax: if (condition1) { if (condition2) { ... } }
Inner if runs only if outer if is true.
Use to test multiple related conditions step-by-step.

Full Transcript

This example shows nested if statements in Java. First, the program checks if x is greater than 5. If yes, it then checks if x is less than 15. If both are true, it prints a message. The inner if only runs when the outer if condition is true. If the outer condition is false, the inner if is skipped. This helps test multiple conditions in order.

Practice

1. What does a nested if statement mean in Java?

easy

A. An if statement without any condition

B. An if statement with multiple conditions joined by ||

C. An if statement inside another if statement

D. An if statement that runs only once

Solution

1. Step 1: Understand the meaning of nested if

   A nested if means placing one if statement inside another to check conditions step-by-step.

2. Step 2: Compare options

   Only An if statement inside another if statement describes an if inside another if. Others describe different concepts.

3. Final Answer:

   An if statement inside another if statement -> Option C

4. Quick Check:

   Nested if = if inside if [OK]

Hint: Look for 'if inside if' meaning nested [OK]

Common Mistakes:

• Confusing nested if with multiple conditions in one if
• Thinking nested if runs only once
• Ignoring the inner if statement

2. Which of the following is the correct syntax for a nested if statement in Java?

easy

A. if (x > 0) if y > 0 { System.out.println("Both positive"); }

B. if (x > 0) { if (y > 0) { System.out.println("Both positive"); } }

C. if x > 0 { if y > 0 { System.out.println("Both positive"); } }

D. if (x > 0) { if (y > 0) System.out.println("Both positive") }

Solution

1. Step 1: Check Java syntax rules for if

   Java requires parentheses around conditions and braces for blocks.

2. Step 2: Validate each option

   if (x > 0) { if (y > 0) { System.out.println("Both positive"); } } uses correct parentheses and braces. if (x > 0) if y > 0 { System.out.println("Both positive"); } misses parentheses around y > 0. if x > 0 { if y > 0 { System.out.println("Both positive"); } } misses parentheses and braces. if (x > 0) { if (y > 0) System.out.println("Both positive") } misses semicolon after println.

3. Final Answer:

   if (x > 0) { if (y > 0) { System.out.println("Both positive"); } } -> Option B

4. Quick Check:

   Correct syntax = if (x > 0) { if (y > 0) { System.out.println("Both positive"); } } [OK]

Hint: Remember: conditions need parentheses, blocks need braces [OK]

Common Mistakes:

• Omitting parentheses around conditions
• Forgetting braces for nested blocks
• Missing semicolons after statements

3. What will be the output of this code?

int a = 5;
int b = 10;
if (a > 0) {
  if (b < 5) {
    System.out.println("Inside inner if");
  } else {
    System.out.println("Inside else of inner if");
  }
} else {
  System.out.println("Inside outer else");
}

medium

A. Inside else of inner if

B. Inside outer else

C. Inside inner if

D. No output

Solution

1. Step 1: Evaluate outer if condition

   a = 5, so a > 0 is true, enter outer if block.

2. Step 2: Evaluate inner if condition

   b = 10, b < 5 is false, so else block of inner if runs.

3. Final Answer:

   Inside else of inner if -> Option A

4. Quick Check:

   Outer if true, inner if false -> inner else [OK]

Hint: Check outer if first, then inner if conditions [OK]

Common Mistakes:

• Ignoring the else block of inner if
• Confusing outer else with inner else
• Assuming no output if inner if false

4. Find the error in this nested if code:

int x = 10;
if (x > 5)
  if (x < 20)
    System.out.println("x is between 5 and 20");
  else
    System.out.println("x is 5 or less");

medium

A. Missing braces causing else to pair with wrong if

B. Incorrect condition syntax

C. Missing semicolon after println

D. Variable x not declared

Solution

1. Step 1: Analyze if-else pairing without braces

   Without braces, else pairs with nearest if, here inner if.

2. Step 2: Understand the logic error

   Else prints "x is 5 or less" only if x >= 20, which is wrong logically.

3. Final Answer:

   Missing braces causing else to pair with wrong if -> Option A

4. Quick Check:

   Braces fix else pairing [OK]

Hint: Use braces to avoid else pairing mistakes [OK]

Common Mistakes:

• Assuming else pairs with outer if
• Ignoring braces importance
• Thinking syntax error instead of logic error

5. You want to write a nested if to check if a number is positive and even. Which code correctly does this?

hard

A. if (num > 0) { if (num % 2 = 0) { System.out.println("Positive even"); } }

B. if (num > 0 && num % 2 == 0) System.out.println("Positive even");

C. if (num > 0) if (num / 2 == 0) System.out.println("Positive even");

D. if (num > 0) { if (num % 2 == 0) { System.out.println("Positive even"); } }

Solution

1. Step 1: Check condition for positive number

   First if checks if num > 0, correct for positive check.

2. Step 2: Check condition for even number inside first if

   Inner if uses num % 2 == 0, correct for even check.

3. Final Answer:

   if (num > 0) { if (num % 2 == 0) { System.out.println("Positive even"); } } -> Option D

4. Quick Check:

   Nested if with correct conditions = if (num > 0) { if (num % 2 == 0) { System.out.println("Positive even"); } } [OK]

Hint: Use % 2 == 0 to check even inside positive check [OK]

Common Mistakes:

• Using single = instead of == in condition
• Using division instead of modulo for even check
• Combining conditions without nesting