package example;
//-*- mode:java; encoding:utf-8 -*-
// vim:set fileencoding=utf-8:
//@homepage@
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public final class MainPanel extends JPanel {
    private MainPanel() {
        super(new BorderLayout());

        final JFrame frame = new JFrame("Test - JFrame");
        frame.setDefaultCloseOperation(WindowConstants.HIDE_ON_CLOSE);
        frame.setSize(240, 240);

        JPanel p = new JPanel(new GridLayout(2, 1, 5, 5));
        p.add(makePanel("in center of screen", new JButton(new AbstractAction("frame.setLocationRelativeTo(null)") {
            @Override public void actionPerformed(ActionEvent e) {
                if (frame.isVisible()) {
                    return;
                }
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        })));
        p.add(makePanel("relative to this button", new JButton(new AbstractAction("frame.setLocationRelativeTo(button)") {
            @Override public void actionPerformed(ActionEvent e) {
                if (frame.isVisible()) {
                    return;
                }
                frame.setLocationRelativeTo((Component) e.getSource());
                frame.setVisible(true);
            }
        })));
        add(p);
        setBorder(BorderFactory.createEmptyBorder(5, 5, 5, 5));
        setPreferredSize(new Dimension(320, 240));
    }
    private static JPanel makePanel(String title, JComponent c) {
        JPanel p = new JPanel(new BorderLayout());
        p.setBorder(BorderFactory.createTitledBorder(title));
        p.add(c);
        return p;
    }
    public static void main(String... args) {
        EventQueue.invokeLater(new Runnable() {
            @Override public void run() {
                createAndShowGUI();
            }
        });
    }
    public static void createAndShowGUI() {
        try {
            UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
        } catch (ClassNotFoundException | InstantiationException
               | IllegalAccessException | UnsupportedLookAndFeelException ex) {
            ex.printStackTrace();
        }
        JFrame frame = new JFrame("@title@");
        frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        frame.getContentPane().add(new MainPanel());
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }
}

@@ -113,33 +113,8 @@
 .*;%0A
-import java.awt.event.*;%0A
 impo
@@ -218,37 +218,45 @@
   super(new 
-Border
+Grid
 Layout(
+2, 1, 5, 5
 ));%0A%0A       
@@ -256,22 +256,16 @@
         
-final 
 JFrame f
@@ -418,133 +418,33 @@
    J
-Panel p = new JPanel(new GridLayout(2, 1, 5, 5));%0A        p.add(makePanel(%22in center of screen%22, new JButton(new AbstractActi
+Button center = new JButt
 on(%22
@@ -478,18 +478,17 @@
 (null)%22)
- %7B
+;
 %0A       
@@ -492,71 +492,40 @@
     
-    @Override public void actionPerformed(ActionEvent e) %7B%0A    
+center.addActionListener(e -%3E %7B%0A
     
@@ -565,36 +565,32 @@
                 
-    
 return;%0A        
@@ -589,34 +589,26 @@
             
-  
-  %7D%0A    
+%7D%0A
             
@@ -646,36 +646,32 @@
 l);%0A            
-    
 frame.setVisible
@@ -690,36 +690,21 @@
     
-   
- %7D%0A        %7D))
+%7D
 );%0A
+%0A
         
 p.ad
@@ -703,79 +703,36 @@
     
-p.add(makePanel(%22relative to this button%22, new JButton(new AbstractActi
+JButton relative = new JButt
 on(%22
@@ -768,18 +768,17 @@
 utton)%22)
- %7B
+;
 %0A       
@@ -782,71 +782,42 @@
     
-    @Override public void actionPerformed(ActionEvent e) %7B%0A    
+relative.addActionListener(e -%3E %7B%0A
     
@@ -857,36 +857,32 @@
                 
-   
- 
 return;%0A        
@@ -881,34 +881,26 @@
             
-    %7D%0A    
+%7D%0A
             
@@ -959,36 +959,32 @@
 ));%0A            
-    
 frame.setVisible
@@ -1003,41 +1003,126 @@
     
+%7D);%0A%0A
     
-%7D%0A
     
-    %7D)));%0A        add(p
+add(makePanel(%22in center of screen%22, center));%0A        add(makePanel(%22relative to this button%22, relative)
 );%0A 

use a lambda expression instead of an anonymous class(ActionListener)