immutable-class-example.java

public final class Box {
    private final ArrayList<String> fruits;

    public Box(ArrayList<String> fruits) {
        this.fruits = fruits.clone();
    }

    public Box addFruit(String fruit) {
        final newBox = new Box(this.fruits.clone());
        newBox.fruits.add(fruit);
        return newBox;
    }
    
    public ArrayList<String> getFruits() {
        return this.fruits.clone();
    }
}