GridLayout 大小不会填满所有空间

Question

I need your help for a project that I need to finish tomorrow. I'm trying to implement a tab which will put some value from database. But I'm facing with an issue that I can't resolve. I want to add several layout one by one. Each layout is splitted into 3 columns but these layout (and columns) doesn't take all available space as you can see on this screen:

Here's my code:

package pizzeria;

import java.sql.SQLException;

import javax.swing.*;

import java.awt.*;

public class CarteDesPizzas extends JPanel{

    static GridLayout grid1 = new GridLayout(1,1);

    static GridLayout grid2 = new GridLayout(1,3);

    static GridLayout grid3 = new GridLayout(1,1);

    public static JPanel affichageCarte() throws SQLException ,Exception {
        JLabel label = new JLabel("Carte des pizzas", JLabel.CENTER);
        label.setForeground(new Color(120, 90, 40));

        JPanel selection = new JPanel();
        GridBagLayout grid = new GridBagLayout();
        selection.setLayout(grid);
         
        JPanel header;
        JPanel content;
         
        GridBagConstraints c = new GridBagConstraints();
        c.fill = GridBagConstraints.BOTH;
        c.weightx = 1; 
        c.weighty = 0.1;
        c.gridy = 0;
         
        header = new JPanel(new GridBagLayout());
        header.add(label);
        selection.add(header,c);
         
        content = new JPanel();
        c.weightx = 1; 
        c.weighty = 0.9;
        c.gridy = 1;



        JPanel selection2 = new JPanel(grid2);

        JPanel pinkSelection = new JPanel();
        pinkSelection.setBackground(Color.PINK);

        JPanel redSelection = new JPanel();
        redSelection.setBackground(Color.RED);

        JPanel greenSelection = new JPanel();
        greenSelection.setBackground(Color.GREEN);

        selection2.add(pinkSelection);
        selection2.add(redSelection);
        selection2.add(greenSelection);

        content.add(selection2);

        selection.add(content,c);
        
        return selection;
    }
}

Thank you for your help

Answer 1

A JPanel is a container. It's purpose is to contain other Component s.

GridBagLayout places components in rectangles (cells) in a grid, and then uses the components' preferred sizes to determine how big the cells should be.

A JPanel , by default, has no preferred size. Its size is determined by the sizes of the components it contains. Since the JPanel s in your code contain no components, their preferred size is very small. Hence they appear very small in your GUI.

The simplest solution would be to explicitly assign a preferred size to the JPanel .

In the below code I only set the preferred size for pinkSelection .

import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.GridLayout;

import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;

public class CarteDesPizzas extends JPanel {
    static GridLayout grid1 = new GridLayout(1,1);
    static GridLayout grid2 = new GridLayout(1,3);
    static GridLayout grid3 = new GridLayout(1,1);

    public static JPanel affichageCarte() {
        JLabel label = new JLabel("Carte des pizzas", JLabel.CENTER);
        label.setForeground(new Color(120, 90, 40));

        JPanel selection = new JPanel();
        GridBagLayout grid = new GridBagLayout();
        selection.setLayout(grid);
         
        JPanel header;
        JPanel content;
         
        GridBagConstraints c = new GridBagConstraints();
        c.fill = GridBagConstraints.BOTH;
        c.weightx = 1; 
        c.weighty = 0.1;
        c.gridy = 0;
         
        header = new JPanel(new GridBagLayout());
        header.add(label);
        selection.add(header,c);
         
        content = new JPanel();
        c.weightx = 1; 
        c.weighty = 0.9;
        c.gridy = 1;

        JPanel selection2 = new JPanel(grid2);

        JPanel pinkSelection = new JPanel();
        pinkSelection.setPreferredSize(new Dimension(100, 60));
        pinkSelection.setBackground(Color.PINK);

        JPanel redSelection = new JPanel();
        redSelection.setBackground(Color.RED);

        JPanel greenSelection = new JPanel();
        greenSelection.setBackground(Color.GREEN);

        selection2.add(pinkSelection);
        selection2.add(redSelection);
        selection2.add(greenSelection);

        content.add(selection2);

        selection.add(content,c);
        
        return selection;
    }

    /**
     * Launch the application.
     */
    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                JFrame frame = new JFrame();
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(affichageCarte());
                frame.pack();
                frame.setLocationByPlatform(true);
                frame.setVisible(true);
            }
        });
    }
}

Here is a screen capture:

Answer 2

You are not using GridLayout although you declared such three variables. You are using GridBagLayout with some specific values that lead to what you get.