Change fields via field.set

Question

I don't quite know if this is the right approach for the problem, but I hope, anyone can make that clear to me:
I got two Applications called "app1" and "app2". app2 is a simple swing-application which, to make it simpler, only consists of a JTextField (pseudocode following).
JTextField vlaue_1 = new JTextField("test");
...The application app1 now starts app2 (using Class.forName and Method.invoke). Then, it gets all of app2's fields, in this case value_1, via getDeclaredFields.
import java.lang.reflect.Field;
import java.lang.reflect.Method;
public class app1 {
     public app1() {
          super();
       public static void main(String[] args) throws Exception {
            Class testClass = Class.forName("app2");
            Method mainMethod = findMainMethod(testClass, "main");
            mainMethod.invoke(null, new Object[] { String[] arguments });
            Field[] fields = testClass.getDeclaredFields();
     private static Method findMainMethod(Class clazz) throws Exception {
          Method[] methods = clazz.getMethods();
          for(int i = 0; i < methods.length; i++){
               if(methods.getName().equals(name))
                    return methods[i];
          return null;
Now, app1 knows about the TextField in app2.
And finally, the question is: Can I change the String in app2's value_1 into something different out of app1? For example, app1 says "Hey TextField, you are no 'test' any longer, you are now a 'foo'" and app2 updates its swing-GUI instantly?
I already tried a field.set(Obj arg1, Obj arg2) and got only exceptions, but probably because I don't quite know which objects are meant for arg1 and arg2.
Perhaps someone has some (pseudo-)code to clarify this issue.
Any help would be nice. Thanks

Answer 1

Ok, the original code for app2 is the following (the app doesn't make much sense, was only created for testing this issue):
import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextField;
public class TestApp extends JFrame implements ActionListener{
     public static JTextField wert1 = new JTextField("15");
     public static JTextField wert2 = new JTextField("12");
     public static JLabel ergebnis = new JLabel("0");
     public static JButton berechnen = new JButton("Berechnen");
     public TestApp() {
          JFrame frame = new JFrame("TestApp");
          JPanel north = new JPanel();
          frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
          frame.getContentPane().add(north, BorderLayout.NORTH);
          north.add(wert1, BorderLayout.CENTER);
          north.add(wert2, BorderLayout.CENTER);
          frame.getContentPane().add(ergebnis, BorderLayout.CENTER);
          frame.getContentPane().add(berechnen, BorderLayout.SOUTH);
          berechnen.addActionListener(this);
          frame.pack();
          frame.setVisible(true);
     public static void main(String[] args) {
          TestApp gui = new TestApp();
     public void actionPerformed(ActionEvent event) {
          double ergebnis_1;
          double wert_1 = Double.parseDouble(wert1.getText());
          double wert_2 = Double.parseDouble(wert2.getText());
              ergebnis_1 = wert_1 + wert_2;
              ergebnis.setText(Double.toString(ergebnis_1));
}The code for app1 follows here:
import java.lang.reflect.Field;
import java.lang.reflect.Method;
public class JavaTester {
     public JavaTester() {
          super();
     public static void main(String[] args) throws Exception {
          Class testKlasse = Class.forName(args[0]);
          String[] neueArgs = uebergebeArgs(args);
          Method mainMethode = findeMethode(testKlasse, "main");
          mainMethode.invoke(null, new Object[] { neueArgs });
          Field[] felder = testKlasse.getDeclaredFields();
     private static String[] uebergebeArgs(String[] args) {
          String[] rueckgabe = new String[args.length - 1];
          for(int i=1; i<args.length; i++) {
               rueckgabe[i-1] = args.toLowerCase();
          return rueckgabe;
     private static Method findeMethode(Class klasse, String name) throws Exception {
          Method[] methoden = klasse.getMethods();
          for(int i = 0; i < methoden.length; i++){
               if(methoden[i].getName().equals(name))
                    return methoden[i];
          return null;
I'm sorry that I can't print the stacktrace, because I just don't know, how to call the field.set function.
Is it for e.g. felder[0].set(???, ???)?