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Why to add JPanel to a JLabel, under what circumstance, this situation can arise?

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轻奢々
轻奢々 2020-12-07 03:41

Today while surfing through various questions, I encountered one QUESTION, this seems to me a bit weird, why would one wants to add a JPanel to a JLabel

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  • 时光取名叫无心
    2020-12-07 03:57 
    this seems to me a bit weird, why would one wants to add 
a JPanel to a JLabel,

    yes thats right

    are there any genuine reasons as to such situation can arise, 
so is it just trivial?

    no, isn't trivial, because only JFrame/JDialog/JWindow and JPanel have got pre_implemented LayoutManager, for rest of "Custom JComponent" you have to declare proper LayoutManager, programatically

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  • 谎友^
    2020-12-07 04:00

    Yes there are genuine reasons to want to add components to a JLabel. Since it is trivially easy to set and swap ImageIcons on JLabels, it's not uncommon to want to use them as a backing image for your GUI.

    Edit
    You state:

    Ahha mean to say, If I wanted my container to have a specific background, then I must be using JLabel as the platform, on which such things can reside ? Am I right ?

    No, you don't absolutely have to use a JLabel for this as it is fairly easy to draw a background image in a JPanel if desired. Just draw the image in its paintComponent(...) method.

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  • 无人共我
    2020-12-07 04:07

    An animated image as a BG for the GUI. I use HTML to resize this one (x3), but if it is already the desired size, you could set it directly as the Icon of the label. 

    import java.awt.*;
import javax.swing.*;
import javax.swing.border.EmptyBorder;

class LabelAsBackground {

    public static final String HTML =
        "<html>" +
        "<style type'text/css'>" +
        "body, html { padding: 0px; margin: 0px; }" +
        "</style>" +
        "<body>" +
        "<img src='http://pscode.org/media/starzoom-thumb.gif'" +
        " width=320 height=240>" +
        "";

    LabelAsBackground() {
        JFrame f = new JFrame("Animated Image BG");
        f.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        JLabel contentPane = new JLabel(HTML);
        contentPane.setLayout(new GridLayout());
        JPanel gui = new JPanel(new GridLayout(3,3,15,15));
        gui.setOpaque(false);
        contentPane.add(gui);
        gui.setBorder(new EmptyBorder(20,20,20,20));
        for (int ii=1; ii<10; ii++) {
            gui.add( new JButton("" + ii));
        }
        f.setContentPane(contentPane);
        f.pack();
        //f.setResizable(false); // uncomment to see strange effect..
        f.setVisible(true);
    }

    public static void main(String[] args) {
        //Create the frame on the event dispatching thread
        SwingUtilities.invokeLater(new Runnable(){
            @Override
            public void run() {
                LabelAsBackground lab = new LabelAsBackground();
            }
        });
    }
}

    Not sure if it is 'genuine' or not. That seems a subjective term that requires much clarification. I've never used this method and only just figured it out, fumbling around tonight. ;)

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