Brewlearn Get the app
🔀 Control Flow · Beginner

What you can switch on

int-like types, char, String, enums, and any type with patterns.

🧩 The mysteryYour command parser understands "stop" but ignores "Stop". And when the input is null, the whole app crashes. One switch, three surprises.

What a classic switch accepts

A classic switch works on **byte, short, char, int** (and their wrappers like Integer), **String (since Java 7) and enums. It does not** accept long, float, double or boolean: those need primitive patterns, still a preview feature in Java 25.

long id = 7L;
switch (id) { } // compile error
int n = 7;
switch (n) { }  // fine
🔮 Predict it

Strings in a switch

The user typed GO. What prints?

String cmd = "GO";
switch (cmd) {
    case "go" -> System.out.println("move");
    default -> System.out.println("unknown");
}
  1. move
  2. unknown
  3. move unknown
Show the answer

unknown. String cases are compared with equals(), which is exact and case-sensitive: "GO" is not "go". A common fix is switch (cmd.toLowerCase()).

🔮 Predict it

What about null?

day is null, and there's a default. What happens?

String day = null;
switch (day) {
    case "Sat" -> System.out.println("rest");
    default -> System.out.println("work");
}
  1. work
  2. Nothing is printed
  3. Throws NullPointerException
Show the answer

NullPointerException. default does not catch null. A switch on a null selector throws unless it has an explicit case null.

Handling a missing value

✗ Crashes on null
switch (input) {
    case "y" -> accept();
    default -> reject();
}

If input is null, default never gets a chance: NullPointerException.

✓ Null-safe (Java 21+)
switch (input) {
    case null -> askAgain();
    case "y" -> accept();
    default -> reject();
}

An explicit case null handles the missing value.

Switching on types (Java 21)

Pattern matching lets switch test the type of any object and bind a variable in one go: case Integer i -> matches when o is an Integer and names it i. A when guard adds an extra condition. Cases are tried top to bottom; the first match wins.

Object o = 42;
String d = switch (o) {
    case Integer i -> "int " + i;
    case String s -> "text " + s;
    default -> "other";
};
🔮 Predict it

Guards in action

o holds the Integer 7. What prints?

Object o = 7;
String d = switch (o) {
    case Integer i when i > 10 -> "big int";
    case Integer i -> "small int";
    default -> "other";
};
System.out.println(d);
  1. big int
  2. small int
  3. other
  4. Compile error
Show the answer

small int. The first arm matches the type, but its guard i > 10 is false, so Java moves on. The second arm matches with no guard.

💼 In the real world

In real projects

Command parsers, HTTP methods, event types from JSON: switching on Strings is everywhere. Real input arrives in odd casing and is sometimes missing (null), so production code normalizes the case first and handles null explicitly, or the app crashes on the first weird request.

Key takeaways

  1. Allowed: byte, short, char, int (and wrappers), String, enums
  2. Not allowed classically: long, float, double, boolean (primitive patterns are still preview in Java 25)
  3. String cases compare with equals(), so they're case-sensitive
  4. A null selector throws NullPointerException unless there's a case null
🤯 Did you know?

A switch on Strings is compiled into a switch on each String's hashCode(), followed by equals() checks. That's how it stays fast even with many cases.

Practice questions

Which type can NOT be the selector of a classic switch in Java 25 (without preview features)?

  1. char
  2. String
  3. long
  4. An enum type
Check your answer

long. Classic switch supports int-sized integer types, their wrappers, String and enums. long, float, double and boolean need primitive patterns, still a preview feature in Java 25.

What does this print?

String cmd = "Stop";
switch (cmd) {
    case "stop" -> System.out.println("halt");
    case "go" -> System.out.println("move");
    default -> System.out.println("unknown");
}
  1. halt
  2. unknown
  3. halt unknown
  4. Compile error
Check your answer

unknown. "Stop" and "stop" differ in case, so no case matches and default runs.

Next: loops! Meet while, the loop that might not run even once.