Why is my JFrame not showing?

I'm pretty sure I've done it this way before, but for some reason, the JFrame won't show up when I开发者_开发知识库 run it.

    JLabel originalString =  new JLabel("Original String: " 
                                        + str.getMutator());
    JLabel currentString = new JLabel("Current String: " 
                                      + str.getMutator());
    JLabel finalString =  new JLabel("Final String: " + str.getTarget());

    JPanel panel = new JPanel();
    panel.add(originalString);
    panel.add(currentString);
    panel.add(finalString);

    JFrame frame = new JFrame("Mutating String!");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.getContentPane().add(panel);
    frame.pack();
    frame.setVisible(true);
}

Try to set size or check with the preferred size of your components probably because you call pack().

frame.setSize(x, y);

Your problem must be somewhere else (is the method called does it throw an exception ?) because your code works (I commented the str calls) :

http://img217.imageshack.us/img217/902/screenvlg.png

import javax.swing.*;
public class Test{
    public static void main(String... args){
        JLabel originalString =  new JLabel("Original String: " /*+ str.getMutator()*/);
        JLabel currentString = new JLabel("Current String: "/* + str.getMutator()*/);
        JLabel finalString =  new JLabel("Final String: " /* + str.getTarget()*/);

        JPanel panel = new JPanel();
        panel.add(originalString);
        panel.add(currentString);
        panel.add(finalString);

        JFrame frame = new JFrame("Mutating String!");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().add(panel);
        frame.pack();
        frame.setVisible(true);
    }
}