Develop Reference

I am Using Jbuttons on Jpanel and addding this jpanel on Jlist. I am using addMouseListener on list. Not able to get click on Button on Jpanel

Below is the minimum reproducible code. In MouseClicked method with mouseevent i got that Jpanel is clicked by using getelementat() method.
But which button on JPanel is clicked can not figure. Tried with convert point but making some mistake. Need to check which button on Jpanel is clicked. Need some help.
import javax.swing.*;
import javax.swing.event.ListSelectionEvent;
import javax.swing.event.ListSelectionListener;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
public class JListTest {
private JList list;
private DefaultListModel dataModel ;
private JTableTest tableTest;
private JPanel panel = new JPanel();
public JListTest() {
dataModel = new DefaultListModel();
list = new JList<>(dataModel);
list.addMouseListener(new MouseAdapter() {
#Override
public void mouseClicked(MouseEvent me) {
super.mouseClicked(me);
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
JList target = (JList) me.getSource();
int index = target.locationToIndex(me.getPoint());
JPanel item = (JPanel) target.getModel().getElementAt(index);
Point p=SwingUtilities.convertPoint(target,me.getPoint(),item);
item.getComponentAt(p);
}
});
}
});
list.setCellRenderer(new PanelRenderer());
}
public static void main(String []args){
JListTest test=new JListTest();
test.dataModel.addElement("Lable 1");
test.dataModel.addElement("Lable 2");
test.dataModel.addElement("Lable 3");
JButton button1 = new JButton("Button 1");
JButton button2 = new JButton("Button 2");
test.panel.add(button1);
test.panel.add(button2);
test.dataModel.addElement(test.panel);
test.showUi();
}
public void showUi(){
JFrame.setDefaultLookAndFeelDecorated(true);
JFrame frame = new JFrame("Demo list");
frame.setAlwaysOnTop(true);
frame.setType(Window.Type.UTILITY);
frame.setResizable(true);
frame.getContentPane().setLayout(new BorderLayout());
JScrollPane scrollPane = new JScrollPane(list);
scrollPane.setPreferredSize(new Dimension(400, 250));
frame.getContentPane().add(scrollPane, BorderLayout.NORTH);
frame.setDefaultCloseOperation(JFrame.DO_NOTHING_ON_CLOSE);
frame.setSize(500, 300);
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
class PanelRenderer implements ListCellRenderer {
public Component getListCellRendererComponent(JList list, Object value, int index, boolean isSelected, boolean cellHasFocus) {
if(value instanceof String){
return new DefaultListCellRenderer().getListCellRendererComponent(list,value,index,isSelected,cellHasFocus);
}
return (Component) value;
}
}
}
Blockquote

item.getComponentAt(p);
What is the point of that statement? How can you tell if the code worked or not since you never assign the result of the method to a variable?
Turns out that because the panel is not really a component displayed on the frame you can't just do as I originally suggested.
If you add code like:
JPanel item = (JPanel) target.getModel().getElementAt(index);
System.out.println( item.getBounds() );
You get output like:
java.awt.Rectangle[x=-487,y=-36,width=0,height=0]
Which doesn't make any sense.
So, I changed the logic to assign the bounds to the panel as if it was displayed on the JList:
item.setBounds(target.getCellBounds(index, index));
Now, I get output like:
java.awt.Rectangle[x=0,y=54,width=487,height=36]
Which does make more sense. However, that still doesn't help because if you add:
Point p = SwingUtilities.convertPoint(target,me.getPoint(),item);
System.out.println( p );
You get something like:
java.awt.Point[x=834,y=166]
The conversion of the point does do what I expected.
So, I decided to convert the point manually:
int y = me.getY() - item.getBounds().y;
Point p = new Point(me.getX(), y);
Putting it all together you get something like:
JList target = (JList) me.getSource();
int index = target.locationToIndex(me.getPoint());
JPanel item = (JPanel) target.getModel().getElementAt(index);
item.setBounds(target.getCellBounds(index, index));
int y = me.getY() - item.getBounds().y;
Point p = new Point(me.getX(), y);
JButton button = (JButton)item.getComponentAt(p);
System.out.println(button.getText());
And you get the text of the button when you click on it.
Of course, you get Exceptions if you click anywhere else. I'll leave it up to you do handle the Exception logic.
Note, I see your latest question is about adding labels and a panel to a frame. It is a much better approach to use real components as you can add ActionListeners to your buttons.

How to create multiple JPanels with JTextField input?

I am currently working on my school project to practice vocabulary, I have a method in my GUI that creates new vocabulary and the name of the list, I wanted to create a button that adds more Panels with input fields just this prototype image.
My idea is that when the user clicks
AddMoreButton it will add one JPanel just like P Panel, then the user can write vocabulary to send it to my database, is it possible to create something that?, I tried looping the P panel but it did not not change, any help would be appreciated.
private JPanel SetUpCreate() {
JPanel createPanel = new JPanel();
nameListInput = new JTextField(INPUT_FIELD_WIDTH);
termInput = new JTextField(INPUT_FIELD_WIDTH);
defintionInput = new JTextField(INPUT_FIELD_WIDTH);
p = new JPanel();
doneCreate = new JButton("Done");
doneCreate.addActionListener(new DoneCreateButtonAction());
addMoreButton = new JButton("Add");
addMoreButton.addActionListener(new AddMorePanelsListener());
p.setBorder(new BevelBorder(BevelBorder.RAISED));
p.add(termInput);
p.add(defintionInput);
JScrollPane pane = new JScrollPane(p);
createPanel.add(nameListInput);
createPanel.add(p);
createPanel.add(pane);
createPanel.add(doneCreate);
return createPanel;
}
private class DoneCreateButtonAction implements ActionListener {
public DoneCreateButtonAction() {
super();
}
public void actionPerformed(ActionEvent e) {
String namelist = nameListInput.getText();
String termglosa = termInput.getText();
String defintionglosa = defintionInput.getText();
try {
if (model.createWordList(namelist) && (model.createGlosa(termglosa, defintionglosa))) {
cl.show(cardPanel, "home");
}
} catch (IOException e1) {
JOptionPane.showMessageDialog(frame, "skapelsen av listan fungerar ej.");
}
}
}
private class AddMoreButtonAction implements ActionListener {
public AddMoreButtonAction() {
super();
}
public void actionPerformed(ActionEvent e) {
}
}

What I understand from your question is that you want to add another panel every time the user clicks the Add button and the panel to add contains fields for entering a word and its definition.
I see JScrollPane appears in the code you posted in your question. I think this is the correct implementation. In the below code, every time the user clicks the Add button I create a panel that contains the fields for a single word definition. This newly created panel is added to an existing panel that uses GridLayout with one column. Hence every time a new word definition panel is added, it is placed directly below the last word panel that was added and this GridLayout panel is placed inside a JScrollPane. Hence every time a word definition panel is added, the GridLayout panel height increases and the JScrollPane adjusts accordingly.
import java.awt.BorderLayout;
import java.awt.EventQueue;
import java.awt.GridLayout;
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.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextField;
import javax.swing.WindowConstants;
public class MorPanel implements ActionListener, Runnable {
private static final String ADD = "Add";
private JFrame frame;
private JPanel vocabularyPanel;
#Override
public void run() {
showGui();
}
#Override
public void actionPerformed(ActionEvent actionEvent) {
String actionCommand = actionEvent.getActionCommand();
switch (actionCommand) {
case ADD:
vocabularyPanel.add(createWordPanel());
vocabularyPanel.revalidate();
vocabularyPanel.repaint();
break;
default:
JOptionPane.showMessageDialog(frame,
actionCommand,
"Unhandled",
JOptionPane.ERROR_MESSAGE);
}
}
public JButton createButton(String text) {
JButton button = new JButton(text);
button.addActionListener(this);
return button;
}
public JPanel createButtonsPanel() {
JPanel buttonsPanel = new JPanel();
buttonsPanel.add(createButton(ADD));
return buttonsPanel;
}
private JScrollPane createMainPanel() {
vocabularyPanel = new JPanel(new GridLayout(0, 1));
vocabularyPanel.add(createWordPanel());
JScrollPane scrollPane = new JScrollPane(vocabularyPanel);
return scrollPane;
}
private JPanel createWordPanel() {
JPanel wordPanel = new JPanel();
JLabel wordLabel = new JLabel("Enter Term");
JTextField wordTextField = new JTextField(10);
JLabel definitionLabel = new JLabel("Enter Term Definition");
JTextField definitionTextField = new JTextField(10);
wordPanel.add(wordLabel);
wordPanel.add(wordTextField);
wordPanel.add(definitionLabel);
wordPanel.add(definitionTextField);
return wordPanel;
}
private void showGui() {
frame = new JFrame("Vocabulary");
frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
frame.add(createMainPanel(), BorderLayout.CENTER);
frame.add(createButtonsPanel(), BorderLayout.PAGE_END);
frame.setSize(480, 200);
frame.setLocationByPlatform(true);
frame.setVisible(true);
}
public static void main(String[] args) {
EventQueue.invokeLater(new MorPanel());
}
}

As your code is not an Minimal Reproducible Example, I cannot provide further assistance than this:
Red part: Your main JPanel with BoxLayout
Green part: another JPanel with your JTextField in it.
Purple part: JScrollPane
Blue parts: custom JPanels with 2 panes in them, one on top for the number, one on the bottom for both JTextFields and icon, so I would say GridBagLayout or BoxLayout + FlowLayout
Orange part: JPanel with GridBagLayout or FlowLayout
Each time you clic on the + icon, you just create a new instance of the custom blue JPanel and that's it.

JAVA - Can't add Text Field and Button to container

I'm trying to do a little program that use some buttons and text field.
I was able to create window with JPanel but don't have idea how to add button and text field
The code I'm using is:
public UI() {
sprites = new HashMap();
// spriteCache = stage.getSpriteCache();
JFrame okno = new JFrame ("VoLTE Script");
setBounds(0,0,SZEROKOSC,WYSOKOSC);
JPanel panel = (JPanel)okno.getContentPane();
panel.setLayout (null);
panel.add(this);
okno.setBounds(0,0,800,600);
okno.setVisible(true);
JTextField pole = new JTextField(10);
JButton przycisk = new JButton("teasda");
przycisk.setPreferredSize(new Dimension(300, 350));
przycisk.setLayout(new BorderLayout());
panel.add(przycisk);
przycisk.setVisible(true);
pole.setBounds (300,300,200,200);
pole.setLayout(null);
pole.setVisible(true);
panel.add(pole);
okno.addWindowListener(new WindowAdapter(){
public void windowClosing (WindowEvent e){
System.exit(0);
}
});
okno.setResizable(false);
createBufferStrategy(2);
strategia=getBufferStrategy();
requestFocus();
// addKeyListener(this);
// addMouseListener(this);
}

You need to use the layout properly, when using border layout you need to tell it which border to use (, BorderLayout.NORTH or something), check out the tutorials at oracles page.
P.S. Think of how your naming your fields etc. Naming something "przycisk" just gives me a reason not to read the code further.

Thank You for help and sorry for Polish names(fixed already).
I was able to add Text Area with scroll.
Looks like problem was in panel.add(this); putted before button and text field.
From my understanding if panel.add(this) is set before panel.add(pole); then panel.add(this) is set in front and pole is added but not seen.
Below my actual working code:
...
public UI() {
sprites = new HashMap();
// spriteCache = stage.getSpriteCache();
JFrame okno = new JFrame ("VoLTE Script");
setBounds(0,0,WIDTH,HEIGHT);
JPanel panel = (JPanel)okno.getContentPane();
panel.setLayout (null);
okno.setBounds(0,0,800,600);
okno.setVisible(true);
JTextArea pole = new JTextArea();
pole.setLayout(null);
pole.setLineWrap(true);
//pole.setBackground(Color.BLACK);
pole.setEditable(false);
JScrollPane scroll = new JScrollPane(pole);
scroll.setBounds(25,250,500,300);
scroll.setVerticalScrollBarPolicy(
JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);
panel.add(scroll);
panel.add(this);
okno.addWindowListener(new WindowAdapter(){
public void windowClosing (WindowEvent e){
System.exit(0);
}
});
okno.setResizable(false);
createBufferStrategy(2);
strategia=getBufferStrategy();
requestFocus();
// addKeyListener(this);
addMouseListener(this);
}
...

This code is from this site: Example of Java GUI
//Imports are listed in full to show what's being used
//could just import javax.swing.* and java.awt.* etc..
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JComboBox;
import javax.swing.JButton;
import javax.swing.JLabel;
import javax.swing.JList;
import java.awt.BorderLayout;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
public class GuiApp1 {
//Note: Typically the main method will be in a
//separate class. As this is a simple one class
//example it's all in the one class.
public static void main(String[] args) {
new GuiApp1();
}
public GuiApp1()
{
JFrame guiFrame = new JFrame();
//make sure the program exits when the frame closes
guiFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
guiFrame.setTitle("Example GUI");
guiFrame.setSize(300,250);
//This will center the JFrame in the middle of the screen
guiFrame.setLocationRelativeTo(null);
//Options for the JComboBox
String[] fruitOptions = {"Apple", "Apricot", "Banana"
,"Cherry", "Date", "Kiwi", "Orange", "Pear", "Strawberry"};
//Options for the JList
String[] vegOptions = {"Asparagus", "Beans", "Broccoli", "Cabbage"
, "Carrot", "Celery", "Cucumber", "Leek", "Mushroom"
, "Pepper", "Radish", "Shallot", "Spinach", "Swede"
, "Turnip"};
//The first JPanel contains a JLabel and JCombobox
final JPanel comboPanel = new JPanel();
JLabel comboLbl = new JLabel("Fruits:");
JComboBox fruits = new JComboBox(fruitOptions);
comboPanel.add(comboLbl);
comboPanel.add(fruits);
//Create the second JPanel. Add a JLabel and JList and
//make use the JPanel is not visible.
final JPanel listPanel = new JPanel();
listPanel.setVisible(false);
JLabel listLbl = new JLabel("Vegetables:");
JList vegs = new JList(vegOptions);
vegs.setLayoutOrientation(JList.HORIZONTAL_WRAP);
listPanel.add(listLbl);
listPanel.add(vegs);
JButton vegFruitBut = new JButton( "Fruit or Veg");
//The ActionListener class is used to handle the
//event that happens when the user clicks the button.
//As there is not a lot that needs to happen we can
//define an anonymous inner class to make the code simpler.
vegFruitBut.addActionListener(new ActionListener()
{
#Override
public void actionPerformed(ActionEvent event)
{
//When the fruit of veg button is pressed
//the setVisible value of the listPanel and
//comboPanel is switched from true to
//value or vice versa.
listPanel.setVisible(!listPanel.isVisible());
comboPanel.setVisible(!comboPanel.isVisible());
}
});
//The JFrame uses the BorderLayout layout manager.
//Put the two JPanels and JButton in different areas.
guiFrame.add(comboPanel, BorderLayout.NORTH);
guiFrame.add(listPanel, BorderLayout.CENTER);
guiFrame.add(vegFruitBut,BorderLayout.SOUTH);
//make sure the JFrame is visible
guiFrame.setVisible(true);
}
}
For the future i will recommend you to use the extends JFrame so you can only write a gui like this without initialize a JFrame:
public class CalculatorGUI extends JFrame {
public CalculatorGUI() {
setTitle("Calculator");
setBounds(300, 300, 220, 200);
}}
I suggest you check out a couple of tutorials about how to create a Java Gui or sth.

Replacing a JPanel with a different JPanel

Hi this is a bit of a basic question. In my code I create a gui in a constructor then nest a ActionListener class to handle button changes. This code will create the gui and the action listener runs through the actionPerformed method correctly. However, I've tried multiple ways to change the panel in the gui but I feel like the way I have the program set up it is not possible for this to work. Sorry if this is a repeat but after searching for a while on S.O. I haven't found a good example that would help me with my problem.
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Font;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.ButtonGroup;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JRadioButton;
import org.math.plot.Plot2DPanel;
import org.math.plot.plotObjects.BaseLabel;
public class GraphGui extends JFrame {
//default width and height of the GUI
private static final int WIDTH = 1200;
private static final int HEIGHT = 700;
GraphPlot gp = new GraphPlot();
Plot2DPanel plotPanel =gp.determinePlotToPlot("duration");
/**
* This is the constructor that initializes the JFrame and the layout of the GUI.
* The radio buttons are also created here and grouped accordingly.
*/
public GraphGui() {
//title of GUI
setTitle("VibeTech Graph Gui");
//First JRadioButton for date vs duration
JRadioButton durToDate = new JRadioButton("Duration vs. Date");
durToDate.addActionListener(new RadioButtonListener());
durToDate.setActionCommand("duration");
durToDate.setSelected(true);
//JRadioButton for weight vs date
JRadioButton weightToDate = new JRadioButton("Weight vs. Date");
weightToDate.addActionListener(new RadioButtonListener());
weightToDate.setActionCommand("weight");
//JRadioButton for plan type vs date
JRadioButton planToDate = new JRadioButton("Plan vs. Date");
planToDate.addActionListener(new RadioButtonListener());
planToDate.setActionCommand("level");
//button group of the buttons to display them as one group
ButtonGroup group = new ButtonGroup();
group.add(planToDate);
group.add(weightToDate);
group.add(durToDate);
//create JPanel to add objects to
JPanel jplRadio = new JPanel();
jplRadio.setLayout(new GridLayout(0, 1));
//add radio buttons
jplRadio.add(planToDate);
jplRadio.add(weightToDate);
jplRadio.add(durToDate);
Plot2DPanel dvt = new Plot2DPanel();
dvt.addLinePlot("Duration over Time", gp.getDate(), gp.getDuration());
BaseLabel title = new BaseLabel("Duration over Time", Color.RED,
0.5, 1.1);
title.setFont(new Font("Courier", Font.BOLD, 20));
dvt.addPlotable(title);
dvt.setAxisLabels("Time", "Duration");
setLayout(new BorderLayout());
add(jplRadio, BorderLayout.WEST);
add(plotPanel, BorderLayout.EAST);
setSize(WIDTH, HEIGHT);
setVisible(true);
setDefaultCloseOperation(EXIT_ON_CLOSE);
}
//main method to run program
public static void main(String [ ] args)
{
//create new GUI
#SuppressWarnings("unused")
GraphGui test = new GraphGui();
}
//create a radio button listener to switch graphs on button press
class RadioButtonListener implements ActionListener {
#Override
public void actionPerformed(ActionEvent e) {
if(e.getActionCommand().equals("duration")) {
plotPanel = gp.determinePlotToPlot("duration");
} else if (e.getActionCommand().equals("weight")) {
plotPanel = gp.determinePlotToPlot("weight");
} else if (e.getActionCommand().equals("level")) {
plotPanel = gp.determinePlotToPlot("level");
}
//here is where I tried to do removes, adds, and validates but
//I have trouble getting to the frame itself to remove the JPanel
//component. I think this is a setup problem.
}
}
}

You would need to add the panel and revalidate/repaint the JFrame for it to appear:
add(plotPanel, BorderLayout.EAST);
revalidate();
repaint();
Better to use CardLayout to manage this type of functionality.

Try using CardLayout for switching between panels. Here is my solution for a similar question: https://stackoverflow.com/a/9377623/544983

In swing GUI how to show a JPanel as maximized when the user clicks a button?

I want to maximize a JPanel inside a JFrame when the user clicks a button.What is the best way to achieve this.The view and the data model should be in sync in both the panels,that is the panel which in the JFrame and the maximized one.Please suggest me some solution.
my requirement is: i have a JFrame with 4 JPanels named as
JPanelA,JPanelB,JPanelC,JPanelD
Here the JPanelD contains a JList and
a button below it say "MAXIMIZE
PANEL" button . JList has a JTree
with in it . Sometimes the JList may
have huge set of data and it is not
visible to the user clearly.
So he need to maximize this JPanelD alone to see the contents of the JList clearly.For that he clicks "MAXIMIZE PANEL" button.After the click action ,the JPanelD in the JFrame remains there,also a new JPanel with the same JList data(ie.,the replica of the JPanelD say JPanelDMaximized)should be popped up.This is what i want to do ..

Of course you could do this yourself, but you should really look at JInternalFrame and consider using that for your panel. It will save a bunch of headache.
Edit: Sun's tutorial should get you what you need.

Follow-up to your clarification of the problem:
Take my code, and remove:
maximizedFrame.setUndecorated( true );
and size the frame bigger before you make it visible. That should satisfy the maximize-like behaviour you need.
Your other problem is that you cannot add JPanelD to the two JFrames. The pop-up frame must have its own unique JPanel object (let's call it JPanelE). So you need to:
Initialize and lay out JPanelE like you do JPanelD. That means giving JPanelE its own JList (and JTree, and so on).
Share the ListModel from JPanelD's JList with JPanelE's JList, and so on. The feasibility and details of executing this successfully depends on the specifics of your implementation, and is beyond the scope of your original problem.

Create a JWindow (or an undecorated JFrame) with a JPanel. Leave the JWindow invisible, initially. (The wiring of this new JPanel to the same data model used by the original JPanel is left as an exercise.)
When your maximize-panel button's ActionListener executes, it must:
2.1. Update the (invisible) JWindow's location and size to match the (visible) JFrame's.
2.2. Make your JFrame invisible.
2.3. Make your JWindow visible.
When your unmaximize-panel button's ActionListener executes, it must:
3.1. Update the (invisible) JFrame's location and size to match the (visible) JWindow's.
3.2. Make your JWindow invisible.
3.3. Make your JFrame visible
Example:
package stackoverflow;
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Container;
import java.awt.HeadlessException;
import java.awt.event.ActionEvent;
import javax.swing.AbstractAction;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class MaximizingPanelApp extends JFrame {
private JPanel framePanel;
private JPanel windowPanel;
private JFrame maximizedFrame;
public static void main(String[] args) {
JFrame appFrame = new MaximizingPanelApp();
appFrame.setVisible( true );
}
public MaximizingPanelApp() throws HeadlessException {
super( "Application" );
setDefaultCloseOperation( JFrame.DISPOSE_ON_CLOSE );
initialize();
}
private void initialize() {
// JFrame
{
Container container = getContentPane();
container.setLayout( new BorderLayout() );
framePanel = new JPanel();
framePanel.setBackground( Color.ORANGE );
container.add( framePanel, BorderLayout.CENTER );
JButton button = new JButton( new MaximizeAction() );
container.add( button, BorderLayout.SOUTH );
setSize( 400, 300 );
}
// JWindow
{
maximizedFrame = new JFrame();
Container container = maximizedFrame.getContentPane();
container.setLayout( new BorderLayout() );
windowPanel = new JPanel();
windowPanel.setBackground( Color.ORANGE );
container.add( windowPanel, BorderLayout.CENTER );
JButton button = new JButton( new UnMaximizeAction() );
container.add( button, BorderLayout.SOUTH );
maximizedFrame.setSize( getSize() );
maximizedFrame.setUndecorated( true );
}
}
private class MaximizeAction extends AbstractAction {
private MaximizeAction() {
super( "Maximize" );
}
public void actionPerformed(ActionEvent e) {
maximizedFrame.setSize( getSize() );
maximizedFrame.setLocation( getLocation() );
setVisible( false );
maximizedFrame.setVisible( true );
}
}
private class UnMaximizeAction extends AbstractAction {
private UnMaximizeAction() {
super( "Un-Maximize" );
}
public void actionPerformed(ActionEvent e) {
setLocation( maximizedFrame.getLocation() );
setSize( maximizedFrame.getSize() );
maximizedFrame.setVisible( false );
maximizedFrame.dispose();
setVisible( true );
}
}
}

This depends on the layout manager you use. If you add a JPanel to a JFrame using the default layout manager, and the JFrame only contains the JPanel and nothing else, you'll achieve what you describe.
Here's an example. The JPanel is green; notice how it resizes as you resize the JFrame.
import javax.swing.*;
import java.awt.*;
public class ScratchSpace {
public static void main(String[] args) {
JFrame frame = new JFrame("Stretchy panel demo");
final JPanel panel = new JPanel();
panel.setOpaque(true);
panel.setBackground(Color.GREEN);
panel.setPreferredSize(new Dimension(600, 400));
final JComponent contentPane = (JComponent) frame.getContentPane();
contentPane.setBorder(BorderFactory.createEmptyBorder(10, 10, 10, 10));
frame.getContentPane().add(panel);
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
}