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Containers: the JPanel

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• The JPanel class

  • JPanel:

    A JPanel object is a lightweight (simple) container to hold graphical components I like to imagine a JPanel as a "post-it" sticker (of any size).

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  • Usage of JPanels:

    Hold other "normal" graphical components (such as labels, buttons, etc) Hold other JPanels !!! Yep, you can stick a JPanel on to another JPanel (Just imagine putting a smaller post-it sticker onto a larger one....) It lets you organize other windows in the window

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  • Creating a JPanel:

    JPanel MyPanel = new JPanel();

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  • Adding a graphical object on to a JPanel:

    JLabel L = new JLabel("Hello World !"); JPanel P = new JPanel(); P.add(L);

    Note:

    To display the JPanel, the JPanel must be added on to the JFrame !!!

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  • Example:

    import java.awt.*; import javax.swing.*; public class Frame4a { public static void main(String[] args) { JFrame f = new JFrame("JFrame with a JPanel"); JLabel L = new JLabel("Hello World !"); // Make a JLabel; JPanel P = new JPanel(); // Make a JPanel; P.add(L); // (1) Add lable L to JPanel P f.getContentPane().add(P); // (2) Then add panel P to JFrame f f.setSize(400,300); f.setVisible(true); } }

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  • Example Program:   /home/cs377001/demo/GUI/Frame4a.java                                                
    • Prog file: click here

    How to run the program:

    Right click on link(s) and save in a scratch directory To compile:   javac Frame4a.java To run:          java Frame4a

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  • Why use JPanels ?

    JPanels allow you to group related GUI components inside one JPanel By organizing related components within one single JPanel you can re-arrange the individual JPanels on the JFrame later. When you re-position a JPanel in the JFrame, you will move the entire group of related components Therefore: The JPanel is ideally suited for designing layout of the GUI