Learn Java Strings & Switch – Exercises Online

String text = "Hello";
IO.println(text.length()); // 5

void main() {
    String word = "Programming";
    IO.println(???);
}

Useful String Methods

Strings have lots of built-in methods: .toUpperCase(), .toLowerCase(), .substring(start, end), .indexOf("text"), .replace("old", "new"), .trim() (removes whitespace at the start and end), .contains("text"), .startsWith("prefix").

Since strings are immutable, all of these methods return a new string — the original string stays unchanged.

if (name.equals("Anna")) {
    // ...
}

void main() {
    String input = "yes";

    if (???) {
        IO.println("Let's go!");
    } else {
        IO.println("Cancelled");
    }
}

The String Pool

Java has a string pool — a cache for string literals. If you write "hello" twice in your code, both point to the same object in the pool. That's why == happens to work when you compare two literals — but that's luck, not a rule you should rely on!

Strings created at runtime (e.g. with new String("hello"), by concatenation, or from user input) do not end up in the pool. So: always use .equals().

switch (value) {
    case 1: ...; break;
    case 2: ...; break;
    default: ...;
}

void main() {
    int day = 3;

    switch (day) {
        case 1: IO.println("Monday"); break;
        case 2: IO.println("Tuesday"); break;
        // Add case 3 for "Wednesday"
        default: IO.println("Other day");
    }
}

Switch Expressions (since Java 14)

Modern Java has a more elegant switch variant with ->:

String day = switch (nr) { case 1 -> "Monday"; case 2 -> "Tuesday"; default -> "Other"; };

Advantages: no break needed, it can return a value directly, and the compiler refuses to compile it if a case isn't covered (a switch expression must be exhaustive). The classic switch is still around, though.