[java] Automatically size JPanel inside JFrame

I have a JPanel subclass on which I add buttons, labels, tables, etc. To show on screen it I use JFrame:

MainPanel mainPanel = new MainPanel(); //JPanel subclass

JFrame mainFrame = new JFrame();
mainFrame.setTitle("main window title");
mainFrame.getContentPane().add(mainPanel);
mainFrame.setLocation(100, 100);
mainFrame.pack();
mainFrame.setVisible(true);
mainFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

But when I size the window, size of panel don't change. How to make size of panel to be the same as the size of window even if it was resized?

You need to set a layout manager for the JFrame to use - This deals with how components are positioned. A useful one is the BorderLayout manager.

Simply adding the following line of code should fix your problems:

mainFrame.setLayout(new BorderLayout());

(Do this before adding components to the JFrame)

You need to set a layout manager for the JFrame to use - This deals with how components are positioned. A useful one is the BorderLayout manager.

Simply adding the following line of code should fix your problems:

mainFrame.setLayout(new BorderLayout());

(Do this before adding components to the JFrame)

As other posters have said, you need to change the LayoutManager being used. I always preferred using a GridLayout so your code would become:

MainPanel mainPanel = new MainPanel();
JFrame mainFrame = new JFrame();
mainFrame.setLayout(new GridLayout());
mainFrame.pack();
mainFrame.setVisible(true);

GridLayout seems more conceptually correct to me when you want your panel to take up the entire screen.

As other posters have said, you need to change the LayoutManager being used. I always preferred using a GridLayout so your code would become:

MainPanel mainPanel = new MainPanel();
JFrame mainFrame = new JFrame();
mainFrame.setLayout(new GridLayout());
mainFrame.pack();
mainFrame.setVisible(true);

GridLayout seems more conceptually correct to me when you want your panel to take up the entire screen.

If the BorderLayout option provided by our friends doesnot work, try adding ComponentListerner to the JFrame and implement the componentResized(event) method. When the JFrame object will be resized, this method will be called. So if you write the the code to set the size of the JPanel in this method, you will achieve the intended result.

Ya, I know this 'solution' is not good but use it as a safety net. ;)

You need to set a layout manager for the JFrame to use - This deals with how components are positioned. A useful one is the BorderLayout manager.

Simply adding the following line of code should fix your problems:

mainFrame.setLayout(new BorderLayout());

(Do this before adding components to the JFrame)

If the BorderLayout option provided by our friends doesnot work, try adding ComponentListerner to the JFrame and implement the componentResized(event) method. When the JFrame object will be resized, this method will be called. So if you write the the code to set the size of the JPanel in this method, you will achieve the intended result.

Ya, I know this 'solution' is not good but use it as a safety net. ;)

You need to set a layout manager for the JFrame to use - This deals with how components are positioned. A useful one is the BorderLayout manager.

Simply adding the following line of code should fix your problems:

mainFrame.setLayout(new BorderLayout());

(Do this before adding components to the JFrame)

From my experience, I used GridLayout.

    thePanel.setLayout(new GridLayout(a,b,c,d));

a = row number, b = column number, c = horizontal gap, d = vertical gap.

For example, if I want to create panel with:

• unlimited row (set a = 0)
• 1 column (set b = 1)
• vertical gap= 3 (set d = 3)

The code is below:

    thePanel.setLayout(new GridLayout(0,1,0,3));

This method is useful when you want to add JScrollPane to your JPanel. Size of the JPanel inside JScrollPane will automatically changes when you add some components on it, so the JScrollPane will automatically reset the scroll bar.

If the BorderLayout option provided by our friends doesnot work, try adding ComponentListerner to the JFrame and implement the componentResized(event) method. When the JFrame object will be resized, this method will be called. So if you write the the code to set the size of the JPanel in this method, you will achieve the intended result.

Ya, I know this 'solution' is not good but use it as a safety net. ;)

As other posters have said, you need to change the LayoutManager being used. I always preferred using a GridLayout so your code would become:

MainPanel mainPanel = new MainPanel();
JFrame mainFrame = new JFrame();
mainFrame.setLayout(new GridLayout());
mainFrame.pack();
mainFrame.setVisible(true);

GridLayout seems more conceptually correct to me when you want your panel to take up the entire screen.