Beispielhafte Stack-Implementierung in Java

Stack.java

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interface Stackable {
    boolean isEmpty();
    default int top() { throw new UnsupportedOperationException(); }
    default Stackable pop() { throw new UnsupportedOperationException(); }
    Stackable push(int element);
}

class StackWithElements implements Stackable {
    private int element;
    private Stackable previous;
    static Stackable of(int... elements) {
        Stackable s = new EmptyStack();
        for (int element : elements) {
            s = s.push(element);
        }
        return s;
    }
    StackWithElements(Stackable previous, int element) {
        assert Objects.nonNull(previous);
        this.previous = previous;
        this.element = element;
    }
    public boolean isEmpty() { return false; }
    public Stackable push(int element) {
        return new StackWithElements(this, element);
    }
    public int top() { return element; }
    public Stackable pop() { return previous; }
    @Override
    public String toString() {
        return pop() + " <- " + top(); 
    }
}

class EmptyStack implements Stackable {
    public boolean isEmpty() { return true; }
    public Stackable push(int element) {
        return new StackWithElements(this, element);
    }
    @Override
    public String toString() {
        return "[ ]";
    }
}