public class Stack {

    Object[] objectField;

    public Stack(int maximalGroesse) {
        objectField = new Object[maximalGroesse];
    }

    public void push(Object o) {
        for (int i = 0; i < objectField.length; i++) {
            if (objectField[i] == null) {
                objectField[i] = o;
                break;
            }
        }
    }

    public Object pop() {
        Object o = null;
        for (int i = objectField.length - 1; i >= 0; i--) {
            if (objectField[i] != null) {
                o = objectField[i];
                objectField[i] = null;
                break;
            }
        }
        return o;
    }

    public boolean isEmpty() {
        if (objectField[0] != null) {
            return false;
        }
        return true;
    }

    public static void main(String[] args) {
        Stack st = new Stack(10);
        st.push("a");
        st.push("b");
        st.push("c");
        System.out.println(st.pop());
        System.out.println(st.pop());
        System.out.println(st.pop());
        System.out.println(st.isEmpty());

    }
}

public class Spiegeln {

    public static String spiegeln(String s) {
        String spiegel = "";
        if (s.length() <= 0) {
            spiegel = s;
            return spiegel;
        } else {
            for (int i = s.length() - 1; i >= 0; i--) {
                spiegel = spiegel + s.charAt(i);
            }
        }
        return spiegel;
    }

    public static void main(String[] args) {
        String s = "hallo";
        System.out.println(s + " gespiegelt ist " + spiegeln(s));
    }

}