Problem mit Java :o

import java.util.Scanner;

public class Rechner
{
	public static void main(String args[]) {
		Scanner scanner = new Scanner(System.in);
		int x, y, z;
		
		System.out.println("Bitte 2 Zahlen eingeben: ");
		
		x = scanner.nextInt();
		y = scanner.nextInt();
		
		z = x + y;
		System.out.println("Die Summe aus " + x + " und " + y + " ist " + z);
	}
}

import javax.swing.JOptionPane;

public class Rechner
{
    public static void main(String[] args)
    {
        String eing1, eing2;
        int zahl1, zahl2;
        eing1 = JOptionPane.showInputDialog(null,"Erste Zahl eingeben:");
        eing2 = JOptionPane.showInputDialog(null,"Zweite Zahl eingeben:");
        zahl1 = Integer.parseInt(eing1);
        zahl2 = Integer.parseInt(eing2);

        int su,di,pr;
        float qu;

        su = zahl1 + zahl2;
        di = zahl1 - zahl2;
        pr = zahl1 * zahl2;
        qu = zahl1 % zahl2;

        JOptionPane.showMessageDialog(null, "Die Summe von " +  zahl1
               + " und " + zahl2 + " ergibt " + su + ".");
        JOptionPane.showMessageDialog(null, "Die Differenz von " + zahl1
               + " und " + zahl2 + " ergibt " + di + ".");
        JOptionPane.showMessageDialog(null, "Das Produkt von " + zahl1
               + " und " + zahl2 + " ergibt " + pr + ".");
        JOptionPane.showMessageDialog(null, "Der Quotient von " + zahl1
               + " und " + zahl2 + " ergibt " + qu + ".");
    }           
}

import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

public class APanel extends Panel implements ActionListener{

	
	private GridLayout g1;
	private Button a;
	private Button d;
	private Button c;
	private Button e;
	private Panel p1;
	private TextField tf;
	private TextField tf1;
	private TextField tf2;
	private TextField tf3;

	public APanel() {
		g1 = new GridLayout(5,2);
		p1 = new Panel(g1);

		tf1 = new TextField();
		tf2 = new TextField();
		tf3 = new TextField();

		a = new Button("Addieren");
		d = new Button("Subtrahieren");
		c = new Button("Multiplizeiren");
		e = new Button("Dividieren");

		a.addActionListener(this);
		d.addActionListener(this);
		c.addActionListener(this);
		e.addActionListener(this);




		p1.add(tf1);
		p1.add(a);
		p1.add(tf2);
		p1.add(d);
		p1.add(tf3);
		p1.add(c);
		p1.add(new Panel());
		p1.add(e);


		this.add(p1);

	}
	@Override
	public void actionPerformed(ActionEvent arg0) {


		Button b = (Button) arg0.getSource();   
		if(b == a){

			double z1 = Double.parseDouble(tf1.getText());
			double z2 = Double.parseDouble(tf2.getText());
			tf3.setText(new Double(z1+z2).toString());

		}
		if(b== d) {

			double x1=Double.parseDouble(tf1.getText());
			double x2=Double.parseDouble(tf2.getText());
			tf3.setText(new Double(x1-x2).toString());
		}
		if(b == c) {

			double z1 = Double.parseDouble(tf1.getText());
			double z2 = Double.parseDouble(tf2.getText());
			tf3.setText(new Double(z1*z2).toString());
		}
		if(b == e) {

			double y1 = Double.parseDouble(tf1.getText());
			double y2 = Double.parseDouble(tf2.getText());
			if(y2==0){
				tf3.setText("Divison durch 0 nicht erlaubt");
			}
			else{
				tf3.setText(new Double(y1/y2).toString());
			}
		}
	}
}