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package huiswerk3;import javax.swing.*;import java.awt.*;import java.awt.event.*;/** * * @author Martijn */public class Rekenmachine extends JFrame{    private JPanel textpanel;    private JTextField textvak;    private JPanel knoppenpanel;    private Knoppen knoppen;    public Rekenmachine(){        knoppen = new Knoppen();        textpanel = new JPanel();        knoppenpanel = new Knoppen();        textvak = new JTextField(15);        textvak.setEnabled(false);        textvak.setText("0" + "aawaef"); // this works         textpanel.add(textvak);        textpanel.add(knoppenpanel);       setContentPane(textpanel);    }    public void setTextVak(){        textvak.setText("0" + "aawaef"); // this doesnt work        System.out.println("test"); // this works also    }}