Generic classes

Definition

A generic class works with a type that you choose when you use it, written like Box<String>. The compiler checks the type for you, so you do not need casts.

Example code

A box that holds any one type, and a pair of two types

class Box<T> {
    private T value;

    void set(T value) { this.value = value; }
    T get() { return value; }
}

class Pair<K, V> {
    final K key;
    final V value;
    Pair(K key, V value) { this.key = key; this.value = value; }
}

class Demo {
    public static void main(String[] args) {
        Box<String> name = new Box<>();
        name.set("Asha");
        String text = name.get();                 // no cast needed
        System.out.println(text.toUpperCase());

        Pair<String, Integer> age = new Pair<>("Asha", 30);
        System.out.println(age.key + " is " + age.value);

        // name.set(42);                          // compile error: the box only holds a String
    }
}

// Output:
// ASHA
// Asha is 30