Switch Statement

A lift has a button for each floor. You press 3, and it goes to 3; you don't check "is it floor 1? is it floor 2?" one by one. When a decision depends on one value matching one of several fixed options, Java's switch reads more clearly than a long else-if ladder: it jumps straight to the matching case.

A Switch on a Day Number

public class DayName {
    public static void main(String[] args) {
        int day = 3;
        switch (day) {
            case 1:
                System.out.println("Monday");
                break;
            case 2:
                System.out.println("Tuesday");
                break;
            case 3:
                System.out.println("Wednesday");
                break;
            case 6:
            case 7:
                System.out.println("Weekend");
                break;
            default:
                System.out.println("Another weekday");
        }
    }
}

Wednesday

How it works

1. Line 4 evaluates day once: it's 3.
2. Java jumps straight to case 3: and runs its lines.
3. break on line 13 leaves the switch. Without it, Java would keep going into the next case.
4. Lines 14 and 15 put two labels on one block, so 6 and 7 both print "Weekend".
5. default runs when no case matches, like the final else of a ladder.

Try it yourself: set day to 5, then to 7. Which lines print each time?

Fall-Through: What Happens Without break

public class FallThrough {
    public static void main(String[] args) {
        int day = 2;
        switch (day) {
            case 1: System.out.println("Monday");
            case 2: System.out.println("Tuesday");
            case 3: System.out.println("Wednesday");
                break;
            case 4: System.out.println("Thursday");
        }
    }
}

Tuesday
Wednesday

Case 2 has no break, so after printing "Tuesday", execution falls through into case 3 and prints "Wednesday" too, until it reaches a break. Sometimes that's useful (as with 6 and 7 above); usually it's a bug.

What You Can Switch On

long, float, double and boolean can't be used in a classic switch. Case labels must be constants, and each must be unique: two case 1: labels give duplicate case label.

public class CitySwitch {
    public static void main(String[] args) {
        String city = "Chennai";
        switch (city) {
            case "Mumbai", "Pune" -> System.out.println("Western zone");
            case "Chennai", "Bengaluru" -> System.out.println("Southern zone");
            default -> System.out.println("Other zone");
        }
    }
}

Southern zone

This is the arrow form (->), added in Java 14. Each case runs only its own line, with no fall-through and no break needed, and one case can list several values with commas. The next lesson, "Switch Expressions", builds on it.

Common Mistakes

Forgetting break. The classic switch bug: one case runs into the next. Prefer the arrow form, which has no fall-through.

Using a variable as a case label. case limit: doesn't compile unless limit is a compile-time constant (static final).

Leaving out default. Without it, an unexpected value silently does nothing. Add default to handle or report it.

Under the Hood

A switch on an int usually compiles to a single jump table instruction (tableswitch or lookupswitch), so the JVM goes straight to the right case instead of comparing one by one. A switch on a String is compiled into a switch on the string's hashCode(), followed by an equals() check, which is why a null string fails with a hashCode message.

Interview Corner

Practice

1. Easy: Write a switch that prints the name of a month (1 to 12), with default printing "Invalid month".
2. Harder: Using fall-through on purpose, print the number of days in a month (ignore leap years), grouping 4, 6, 9 and 11 under one block.

Key Takeaways