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How to make JPanel fill the entire JFrame?

I am making an UI in a minecraft plugin. Everything is working, except I have a JPanel and it doesn't fill the whole JFrame. So what I want is the JPanel fill the entire JFrame even if we re-scale the window.
I use Layout manager (FlowLayout) for the JPanel.
I tried using a Layout manager for the JFrame, well it didn't solved my problem because it didn't resize the JPanel.. I tried setting the size of the JPanel to the JFrame's size, but when it's resized it doesn't scale with it.
So, how can I do this?
My plugin creates a button for every player and when I click the button it kicks the player.
My code (I can't really post less because I don't know where I need to change something):
public static JFrame f;
public static JTextField jtf;
public static JPanel jp;
public static void creategui()
{
System.out.println("GUI created.");
f = new JFrame("Players");
jp = new JPanel();
jp.setLayout(new FlowLayout(FlowLayout.LEFT));
jp.setBackground(Color.GRAY);
jtf = new JTextField("Reason");
jtf.setPreferredSize(new Dimension(200,20));
jtf.setToolTipText("Write the reason here.");
jp.setSize(new Dimension(200,200));
f.setLayout(null);
f.setSize(500,500);
f.setVisible(true);
jp.add(jtf);f.add(jp, BorderLayout.CENTER);
for (final Player p : Bukkit.getOnlinePlayers())
{
System.out.println("Looping.");
final JButton b = new JButton();
b.setName(p.getName());
b.setText(p.getName());
b.setToolTipText("Kick " + b.getText());
b.setBackground(Color.GREEN);
b.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
if (!b.getBackground().equals(Color.RED))
{
Bukkit.getScheduler().runTask(main, new Runnable() {
public void run() {
Bukkit.getPlayer(b.getText()).kickPlayer(jtf.getText());
b.setBackground(Color.RED);
}
});
}
}
});
jp.add(b);
System.out.println("Button added.");
}
f.add(jp, BorderLayout.CENTER);
}

The question should include an mcve reproducing the problem so we can test it.
It could look like this :
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.util.Arrays;
import java.util.List;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextField;
public class Mcve {
private static List<String> players = Arrays.asList(new String[]{"Player A", "Player B"});
public static void main(String[] args) {
creategui();
}
public static void creategui()
{
JPanel jp = new JPanel();
jp.setBackground(Color.GRAY);
JTextField jtf = new JTextField("Reason");
jtf.setPreferredSize(new Dimension(200,20));
jtf.setToolTipText("Write the reason here.");
jp.setSize(new Dimension(200,200));
jp.add(jtf);
for (final String p : players)
{
final JButton b = new JButton();
b.setText(p);
b.setBackground(Color.GREEN);
b.addActionListener(e -> {
if (!b.getBackground().equals(Color.RED))
{
b.setBackground(Color.RED);
}
});
jp.add(b);
}
JFrame f = new JFrame("Players");
f.setLayout(null);
f.setSize(500,500);
f.add(jp, BorderLayout.CENTER);
f.setVisible(true);
}
}
To make the JPanel fill the entire frame simply remove this line :
f.setLayout(null);
and let the default BorderLayout manager do its work.
Here is a modified version with some additional comments:
public class Mcve {
private static List<String> players = Arrays.asList(new String[]{"Player A", "Player B"});
public static void main(String[] args) {
creategui();
}
public static void creategui()
{
JPanel jp = new JPanel();
jp.setBackground(Color.GRAY);
JTextField jtf = new JTextField("Reason");
jtf.setPreferredSize(new Dimension(200,20));
jtf.setToolTipText("Write the reason here.");
jp.setPreferredSize(new Dimension(250,200)); // set preferred size rather than size
jp.add(jtf);
for (final String p : players)
{
final JButton b = new JButton();
b.setText(p);
b.setBackground(Color.GREEN);
b.addActionListener(e -> {
if (!b.getBackground().equals(Color.RED))
{
b.setBackground(Color.RED);
}
});
jp.add(b);
}
JFrame f = new JFrame("Players");
//f.setLayout(null); null layouts are bad practice
//f.setSize(500,500); let layout managers set the sizes
f.add(jp, BorderLayout.CENTER);
f.pack();
f.setVisible(true);
}
}

A 1x1 grid layout does the job quite nicely.
window = new JFrame();
panel = new JPanel();
window.setLayout(new java.awt.GridLayout(1, 1));
window.add(panel);

Either set the layout manager for jp (the JPanel in the code you posted) to BorderLayout and add jtf (the JTextField in the code you posted) to the CENTER of jp, as in:
f = new JFrame();
jp = new JPanel(new BorderLayout());
jtf = new JTextField(30); // number of columns
jp.add(jtf, BorderLayout.CENTER);
f.add(jp, BorderLayout.CENTER);
or dispense with jp and add jtf directly to f (the JFrame in the code you posted), as in:
f = new JFrame();
jtf = new JTextField(30);
f.add(jtf, BorderLayout.CENTER);
The key is that the CENTER component of BorderLayout expands to fill the available space.

So I fixed it somehow, this is the code:
public static void creategui()
{
System.out.println("GUI created.");
f = new JFrame("Players");
jp = new JPanel();
jp.setBackground(Color.GRAY);
jp.setSize(200,200);
jtf = new JTextField(30);
jtf.setToolTipText("Write the reason here.");
jp.add(jtf);
for (final Player p : Bukkit.getOnlinePlayers())
{
System.out.println("Looping.");
final JButton b = new JButton();
b.setName(p.getName());
b.setText(p.getName());
b.setToolTipText("Kick " + b.getText());
b.setBackground(Color.GREEN);
b.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
if (!b.getBackground().equals(Color.RED))
{
Bukkit.getScheduler().runTask(main, new Runnable() {
public void run() {
getplr(b.getText()).kickPlayer(jtf.getText());
b.setBackground(Color.RED);
}
});
}
}
});
jp.add(b);
System.out.println("Button added.");
}
f.setLayout(new BorderLayout());
f.add(jp, BorderLayout.CENTER);
f.setSize(500,500);
f.pack();
f.setVisible(true);
}

change JLabel of a panel depending on Jbutton of another panel in the same Jframe

I have constructed a class for the JPanel with several JButtons.Inside this class I want to construct another JPanel with JLabels that will change depending on the actionPerformed on the JButtons of the first JPanel.Finally, I want to add these 2 panels on the same Jframe. Can all these be done within the class of the first Panel?Otherwise, which is a better approach for this problem?

Yes, you can. One way you could accomplish this is with anonymous inner classes (saves keystrokes):
import java.awt.BorderLayout;
import java.awt.event.*;
import javax.swing.*;
public class Foo {
JLabel one;
JLabel two;
public static void main(String[] args) {
(new Foo()).go();
}
public void go() {
JFrame frame = new JFrame("Test");
// Panel with buttons
JPanel buttonPanel = new JPanel();
JButton changeOne = new JButton("Change One");
changeOne.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent event) {
one.setText("New text for one");
}
}
buttonPanel.add(changeOne);
JButton changeTwo = new JButton("Change Two");
changeTwo.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent event) {
two.setText("New text for two");
}
}
buttonPanel.add(changeTwo);
frame.add(buttonPanel, BorderLayout.NORTH);
// Panel with labels
JPanel labelPanel = new JLabel();
one = new JLabel("One");
labelPanel.add(one);
two = new JLabel("Two");
labelPanel.add(two);
// Set up the frame
frame.add(labelPanel, BorderLayout.SOUTH);
frame.setBounds(50, 50, 500, 500);
frame.setDefaultCloseAction(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
}
}

Adding picture to JFrame from another class java

I am trying to make a program that reads a file chosen by the user, and after reading the file - the suffix "txt" is changed to "gif" and the file is saved as a picture (which is in the same catalogue as the file). The thing is, this picture variable gets its value in the "actionPerformed-method" and after that I want to add it to a frame in another class- but it doesn't show. Here's the code in my OptionsPane-class:
public class OptionsPane extends JComponent implements ActionListener{
private JButton buttonOne = new JButton("Alt.1");
private JButton buttonTwo = new JButton("Alt.2");
private JButton buttonThree = new JButton("Alt.3");
private int option;
private JButton buttonChoose = new JButton("Choose file");
private FileHandler filehandler;
private String picture;
private JLabel picLabel;
public OptionsPane(){
JLabel label = new JLabel("Choose optimization method", SwingConstants.CENTER);
JPanel subPanel = new JPanel();
label.setForeground(Color.CYAN);
label.setFont(new Font("Tahoma", Font.BOLD, 15));
this.setLayout(new BoxLayout(this, BoxLayout.Y_AXIS));
this.add(label);
buttonOne.addActionListener(this);
buttonTwo.addActionListener(this);
buttonThree.addActionListener(this);
buttonChoose.addActionListener(this);
subPanel.setBackground(Color.DARK_GRAY);
subPanel.add(buttonOne);
subPanel.add(buttonTwo);
subPanel.add(buttonThree);
subPanel.add(buttonChoose);
this.add(subPanel);
}
#Override
public void actionPerformed(ActionEvent e) {
if(e.getSource() == buttonOne){
option = 1;
System.out.println("You clicked button 1!");
}else if(e.getSource() == buttonTwo){
option = 2;
System.out.println("You clicked button 2!");
}else if(e.getSource() == buttonThree){
option = 3;
System.out.println("You clicked button 3!");
}else if(e.getSource() == buttonChoose){
System.out.println("hello");
option = 4;
filehandler = new FileHandler();
filehandler.read();
picture = filehandler.getFilePath().replaceFirst("txt", "gif");
picLabel = new JLabel(new ImageIcon(picture));
this.add(picLabel);
}
}
}
The frame is in the "MainFrame"-class, which looks like this at the moment:
public class MainFrame extends JFrame{
private JFrame frame = new JFrame();
private String picture;
private JLabel picLabel;
public MainFrame(){
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setPreferredSize(new Dimension(1300, 800));
frame.getContentPane().setBackground(Color.DARK_GRAY);
frame.setLayout(new BoxLayout(frame.getContentPane(), BoxLayout.Y_AXIS));
OptionsPane optionspane = new OptionsPane();
frame.add(optionspane);
frame.pack();
frame.setVisible(true);
frame.setResizable(true);
}
}
Why isn't the picture visible in the mainframe?
EDIT
It works now!
https://stackoverflow.com/a/22380387/3271504
Thank you for your help #arooaroo . I tried to write down some of what you wrote, but it still didn't work when I wanted to add an image based on what file the user had chosen (for example if the user chose file text1.txt i wanted the corresponding picture "text1.gif" to show up). With your help, the picture showed up when I typed a specific pathway with "/"-slashes, but when I chose a file and tried to load the picture from the file pathway, it didn't show and that is because it had backslashes in the pathways. This is how it should be (such an irritating problem):
#Override
public void actionPerformed(ActionEvent e) {
if(e.getSource() == buttonOne){
option = 1;
System.out.println("You clicked button 1!");
}else if(e.getSource() == buttonTwo){
option = 2;
System.out.println("You clicked button 2!");
}else if(e.getSource() == buttonThree){
option = 3;
System.out.println("You clicked button 3!");
}else if(e.getSource() == buttonChoose){
filehandler = new FileHandler();
filehandler.read();
filepath = filehandler.getFilePath();
picture = filepath.replaceFirst("txt", "gif");
picture = picture.replaceAll("\\\\", "/");
ImageIcon icon = new ImageIcon(picture);
mainFrame.setPicture(icon);
}
Thank you for your help!

Once you separate your GUI code in to separate classes - which is a Good Thing - you will find the eternal challenge for GUI programming is allowing for clean communication between them where there are inter-dependencies.
In this instance perhaps the simplest approach is to pass in a reference of MainFrame into OptionsPane.
Let's assume you create an additional method in MainFrame for setting the picture:
public class MainFrame extends JFrame{
// all instance vars as before
public MainFrame() {
// same as before except for this line...
OptionsPane optionspane = new OptionsPane(this);
}
public void setPicture(JLabel pictureLabel) {
// add code here for adding the picture...
// That's an exercise for yourself, or another question ;)
}
}
Then in your OptionsPane class:
....
private MainFrame mainFrame; // add a new instance var
public OptionsPane(MainFrame mainFrame) {
this.mainFrame = mainFrame;
// ... rest of the code same as before
}
#Override
public void actionPerformed(ActionEvent e) {
//...
picture = filehandler.getFilePath().replaceFirst("txt", "gif");
picLabel = new JLabel(new ImageIcon(picture));
mainFrame.setPicture(picLabel); // <-- This is where you communicate with the mainFrame instance
//...
}
EDIT
Although my original answer provided a valid and correct solution, it's clear that the OP requires a fully working example, including the code to load display the resulting image. Here's a sample program.
public class OptionsPane extends JComponent implements ActionListener {
private JButton buttonOne = new JButton("Alt.1");
private JButton buttonTwo = new JButton("Alt.2");
private JButton buttonThree = new JButton("Alt.3");
private int option;
private JButton buttonChoose = new JButton("Choose file");
private String picture;
private JLabel picLabel;
private MainFrame mainFrame;
public OptionsPane(MainFrame mainFrame) {
this.mainFrame = mainFrame;
JLabel label = new JLabel("Choose optimization method", SwingConstants.CENTER);
JPanel subPanel = new JPanel();
label.setForeground(Color.CYAN);
label.setFont(new Font("Tahoma", Font.BOLD, 15));
this.setLayout(new BoxLayout(this, BoxLayout.Y_AXIS));
this.add(label);
buttonOne.addActionListener(this);
buttonTwo.addActionListener(this);
buttonThree.addActionListener(this);
buttonChoose.addActionListener(this);
subPanel.setBackground(Color.DARK_GRAY);
subPanel.add(buttonOne);
subPanel.add(buttonTwo);
subPanel.add(buttonThree);
subPanel.add(buttonChoose);
this.add(subPanel);
}
#Override
public void actionPerformed(ActionEvent e) {
// For sake of simplicity I'm ignoring the original button logic here
// and focussing on just getting an icon loaded in the parent frame...
ImageIcon icon = new ImageIcon("/path/to/test/image.png");
// Just pass the icon itself rather than a new label.
mainFrame.setPicture(icon);
}
}
public class MainFrame {
// No need to extend JFrame if you're using a JFrame instance variable
private JFrame frame = new JFrame();
private JLabel picLabel;
private JPanel mainPanel;
public MainFrame() {
mainPanel = new JPanel(new BorderLayout());
mainPanel.setBackground(Color.DARK_GRAY);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setPreferredSize(new Dimension(1300, 800));
OptionsPane optionspane = new OptionsPane(this);
mainPanel.add(optionspane, BorderLayout.NORTH);
picLabel = new JLabel();
picLabel.setHorizontalAlignment(JLabel.CENTER);
mainPanel.add(picLabel, BorderLayout.CENTER);
frame.getContentPane().add(mainPanel);
frame.pack();
frame.setVisible(true);
frame.setResizable(true);
}
public void setPicture(ImageIcon icon) {
picLabel.setIcon(icon);
}
public static void main(String[] args) {
new MainFrame();
}
}
Note I've done a couple of things differently. Personally I always create a JPanel and set that up as the primary layer rather and add that directly to the frame rather than messing with the rootPane. And I used the BorderLayout in this example as it's much simpler.
The other thing is to add the JLabel which is to hold the picture to the GUI in the initial set up. Then you'll see I'm only changing its icon in the setPicture() method rather than adding a new JLabel on each instance.

CardLayout (swing) with action listeners on buttons?

I've been trying to figure out CardLayout with action listeners on button
(so like - starts on a load-up page- and on a button click switches to a different "card"
my code won't even run right now i'm not entirely sure why - most implementations I can find use ItemListeners and Combo Boxes
The basic process I've done is create a master JPanel, but my cards JPanel onto the master JPanel, but my different cards into the cards JPanel, then add the master JPanel to the frame to display...
Also, for one of my cards I only need to display a picture - I previously implemented this by just creating a new pop-up window but It would be nice to be able to switch the frame to show it... I don't know why I can't figure this out
Here's my code:
import java.awt.*;
/**
* Game
* Main class that specifies the frame and widgets of the GUI
*/
public class Game implements Runnable {
public void run(){
final String ON_OPEN = "Welcome!"; //Opening frame
final String GAME = "Play!"; // Game Frame
final String STATS = "Stats"; // Post-Game Stat Frame
final String HELP = "Help"; //tutorial frame
JPanel cards = new JPanel();
JPanel master; // a panel for the card layout
final JFrame frame = new JFrame(ON_OPEN);
frame.setLocation(500,200);
//Create the master layout for the program
master = (JPanel) frame.getContentPane();
master.setLayout(new BorderLayout()); // creating master layout
//Create panel for all the cards in CardLayout
final CardLayout cLay = new CardLayout();
cards.setLayout(cLay);
// all the cards
final JPanel help = new JPanel();
final JPanel stats = new JPanel();
final JPanel game = new JPanel (new BorderLayout());
final JPanel open = new JPanel (new FlowLayout());
// setting up ON_OPEN layout - uses JPanel open
final ImageIcon img = new ImageIcon("Instructions.png", "My Instructions..."); // the image I want shown under HELP card
final JButton info = new JButton("Help");
info.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
// cLay.show(help, HELP); // WHAT I NORMALLY SHOULD BE DOING, RATHER JUST MAKE A NEW FRAME FOR THIS THOUGH
// frame.pack();
final JFrame infoFrame = new JFrame("Tutorial");
infoFrame.setLocation(500,50);
JLabel tutorialImg = new JLabel(img);
// int w = img.getIconWidth();
// int h = img.getIconHeight();
//infoFrame.setSize(w, h);
infoFrame.pack();
infoFrame.add(tutorialImg);
infoFrame.setVisible(true);
}
});
open.add(info); // the open-tutorial button
//Add them to the cards JPanel
cards.add(open, ON_OPEN);
cards.add(help, HELP);
cards.add(stats, STATS);
cards.add(game, GAME);
//Add the cards panel to the Master layout panel
master.add(cards);
// This code is all commented out because I'm not sure what I'm doing here...
// frame.add(cards);
// cLay.show(cards, ON_OPEN);
// frame.add(open, BorderLayout.CENTER);
// Main playing area - I want this to be shown in the GAME card...
GridLayout tileGrid = new GridLayout(4,4);
final JPanel grid = new JPanel(tileGrid);
// game.add(grid, BorderLayout.CENTER);
// grid.setLayout(tileGrid);
// frame.add(grid, BorderLayout.CENTER);
// Input - holds typing box
// final JPanel status_panel = new JPanel();
// frame.add(cards, BorderLayout.CENTER);
// frame.add(open, BorderLayout.CENTER);
final JTextField typingArea = new JTextField();
typingArea.setFocusTraversalKeysEnabled(false);
typingArea.setEditable(true);
typingArea.setFocusable(true);
typingArea.requestFocus();
frame.add(typingArea, BorderLayout.SOUTH);
typingArea.addKeyListener(new KeyAdapter() {
public void keyPressed (KeyEvent e) {
if (e.getKeyCode() == KeyEvent.VK_ENTER) { // enter key is pressed
String userWord = typingArea.getText().toLowerCase();
typingArea.setText("");
}
}
});
final JLabel status = new JLabel("Running...");
// status_panel.add(status);
// Reset button
final JPanel control_panel = new JPanel();
frame.add(control_panel, BorderLayout.NORTH);
]
// Put the frame on the screen
frame.pack();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
}
public static void main(String[] args){
SwingUtilities.invokeLater(new Game());
}
}

Problems:
Your code doesn't compile for us since we don't have the JLetterField class.
You're trying to add the JFrame's contentPane back on itself, and causes an exception and doesn't make sense.
Edit 1:
Your latest code shows you putting everything into one very large run() method but in doing so, you loose much and gain nothing.
I suggest getting rid of the Runnable interface, there's no need for it, and creating a true OOP compliant class, one with private fields and public and private methods.
Your actionPerformed method shows no attempt at changing the CardLayout's displayed card.
I suggest that you get rid of the code to show a new window and try to place card swapping code there.
Make your CardLayout and the card-displaying JPanel fields of the class so that other methods can access them and call their methods.
Edit 2:
For example the following code shows the swapping of cards using 3 JButtons. One to get the previous card, one to get the next card, and one to show how to get a specific card (here the 2nd):
import java.awt.BorderLayout;
import java.awt.CardLayout;
import java.awt.Dimension;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import javax.swing.*;
#SuppressWarnings("serial")
public class CardLayoutEg extends JPanel {
private static final String[] CARD_LABELS = { "one", "two", "three", "four",
"five", "six", "seven", "eight", "nine", "ten" };
private static final int PREF_W = 400;
private static final int PREF_H = PREF_W;
private CardLayout cardlayout = new CardLayout();
private JPanel cardHolder = new JPanel(cardlayout);
private Action[] actions = { new ShowPreviousAction(), new ShowNextAction(),
new ShowTwoCardAction() };
public CardLayoutEg() {
for (String cardLabelText : CARD_LABELS) {
JLabel cardLabel = new JLabel(cardLabelText, SwingConstants.CENTER);
cardHolder.add(cardLabel, cardLabelText);
}
JPanel btnPanel = new JPanel(new GridLayout(1, 0, 5, 0));
for (Action action : actions) {
btnPanel.add(new JButton(action));
}
setLayout(new BorderLayout());
add(cardHolder, BorderLayout.CENTER);
add(btnPanel, BorderLayout.SOUTH);
}
#Override
public Dimension getPreferredSize() {
return new Dimension(PREF_W, PREF_H);
}
private class ShowPreviousAction extends AbstractAction {
public ShowPreviousAction() {
super("Previous");
}
#Override
public void actionPerformed(ActionEvent e) {
cardlayout.previous(cardHolder);
}
}
private class ShowNextAction extends AbstractAction {
public ShowNextAction() {
super("Next");
}
#Override
public void actionPerformed(ActionEvent e) {
cardlayout.next(cardHolder);
}
}
private class ShowTwoCardAction extends AbstractAction {
public ShowTwoCardAction() {
super("Show Two");
}
#Override
public void actionPerformed(ActionEvent e) {
cardlayout.show(cardHolder, CARD_LABELS[1]);
}
}
private static void createAndShowGui() {
CardLayoutEg mainPanel = new CardLayoutEg();
JFrame frame = new JFrame("CardLayout Example");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(mainPanel);
frame.pack();
frame.setLocationByPlatform(true);
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGui();
}
});
}
}

how can I make this class an applet

I have the following class which is a simple gui, and I would like to make it an applet so it can be displayed in the browser. I know how to embed the code into an html page(got that done)... but how can make my class an applet? Also, I assuming I don't need a web server just to display the applet in my browser...
package tester1;
import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
public class PanelTest implements ActionListener {
JFrame frame;
JLabel inputLabel;
JLabel outputLabel;
JLabel outputHidden;
JTextField inputText;
JButton button;
JButton clear;
JButton about;
public PanelTest() {
frame = new JFrame("User Name");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setLayout(new GridLayout(3, 2, 10, 10));
//creating first row
JPanel row1 = new JPanel();
inputLabel = new JLabel("Your Name");
inputText = new JTextField(15);
// FlowLayout flow1 = new FlowLayout(FlowLayout.CENTER, 10, 10);
// row1.setLayout(flow1);
row1.add(inputLabel);
row1.add(inputText);
frame.add(row1);
//creating second row
JPanel row2 = new JPanel();
button = new JButton("Display");
clear = new JButton("Clear");
about = new JButton("About");
button.addActionListener(this);
clear.addActionListener(this);
about.addActionListener(new displayAbout());
row2.add(button);
row2.add(clear);
row2.add(about);
frame.add(row2);
//creating third row
JPanel row3 = new JPanel();
outputLabel = new JLabel("Output:", JLabel.LEFT);
outputHidden = new JLabel("", JLabel.RIGHT);
// FlowLayout flow2 = new FlowLayout(FlowLayout.CENTER, 10, 10);
// row3.setLayout(flow2);
row3.add(outputLabel);
row3.add(outputHidden);
frame.add(row3);
frame.pack();
frame.setVisible(true);
}
//same method listen for two different events
#Override
public void actionPerformed(ActionEvent e) {
String command = e.getActionCommand();
if(command.equals("Display")) {
outputHidden.setText(inputText.getText());
}
if(command.equals("Clear")) {
outputHidden.setText("");
inputText.setText("");
}
}
//another way to listen for events
class displayAbout implements ActionListener {
#Override
public void actionPerformed(ActionEvent e) {
JOptionPane.showMessageDialog(frame, "Username 1.1 \n by Jorge L. Vazquez");
}
}
public static void main(String[] args) {
PanelTest frameTest = new PanelTest();
}
}

Use a JApplet rather than a JFrame. Make sure you read the relevant Java Tutorial, which covers the applet lifecycle methods like init, start, stop, and destroy.
As a side note, you should not be building your UI outside of the event dispatch thread.

Use a JApplet instead of a JFrame like veer said, but you must also remove frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);, frame.pack();, and frame.setVisible(true);
Also, replace main(String[] args) with init().