Chapter 11: if-else Statement in Java

This chapter is only about if with else: exactly two paths. Either the condition is true and the first block runs, or it is false and the else block runs. Long chains of conditions belong to Chapter 12.

1. Topic title

The if-else statement: choosing between two mutually exclusive actions

2. What it means

Shape:

if (condition) {
    // when true
} else {
    // when false
}

Exactly one of the two blocks runs. There is no third option in plain if-else—if you need more, you stack else if next chapter or use switch in Chapter 14.

3. Why it is used

Binary decisions are everywhere: pass / fail, logged in / guest, payment success / failure, adult / not for age-gated content. if-else models that cleanly when you only care about two outcomes.

4. Real-world example

An ATM checks PIN length before sending anything to the bank:

• If length is 4 digits, proceed to the next screen.
• Else show “Invalid PIN format” and stay on the entry screen.

Two outcomes, one structure. (Real ATMs do more validation; this is the shape.)

5. Java code example

public class IfElseDemo {
    public static void main(String[] args) {
        int marks = 52;
 
        if (marks >= 40) {
            System.out.println("Result: Pass");
        } else {
            System.out.println("Result: Fail");
        }
 
        boolean isWeekend = false;
 
        if (isWeekend) {
            System.out.println("Sleep in.");
        } else {
            System.out.println("School or office day.");
        }
 
        int age = 16;
 
        if (age >= 18) {
            System.out.println("Ticket: adult pricing");
        } else {
            System.out.println("Ticket: minor pricing");
        }
    }
}

Output:

Result: Pass
School or office day.
Ticket: minor pricing

6. Explanation of code

• First if-else: one branch prints Pass, the other Fail. marks is only checked once for that pair.
• Second pair: isWeekend is false, so the else branch runs.
• Third pair: age branch—only one pricing message prints.

The else has no condition—it means “everything the if did not catch.”

7. Common mistakes

Attaching else to the wrong if in nested code — indentation lies; braces decide. Chapter 13 digs into nesting; here, keep programs flat.

Using if-else when you need three or more separate cases — you can nest if-else inside else, but that gets messy fast; Chapter 12’s ladder is often clearer.

Empty if with work only in else — sometimes you should flip the condition for readability: if (!ok) { ... } else { ... } vs positive check—pick the version a human reads faster.

8. Best practices

Put the “happy path” or simpler branch first when it helps reading—teams disagree; consistency with your project matters more than dogma.

Avoid else after return in the if block when the if already exits the method—some style checkers flag redundant else (optional style).

Keep both blocks short; if each side is twenty lines, extract methods (Chapter 28+).

9. Small practice task

Read a double temperature (you can hard-code 36.5 first). Print Normal range if it is strictly below 38.0, else print Check for fever. Use only if-else—no else if.

Beginner tip

Trace with paper: draw a line from the condition to true branch or false branch. You should never feel like both ran.