swing GridLayout How GridLayout works

Example

A GridLayout is a layout manager which places components inside a grid with equal cell sizes. You can set the number of rows, columns, the horizontal gap and the vertical gap using the following methods:

• setRows(int rows)
• setColumns(int columns)
• setHgap(int hgap)
• setVgap(int vgap)

or you can set them with the following constructors:

• GridLayout(int rows, int columns)
• GridLayout(int rows, int columns, int hgap, int vgap)

If the number of rows or columns is unknown, you can set the respective variable to 0. For example:

new GridLayout(0, 3)

This will cause the GridLayout to have 3 columns and as many rows as needed.

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The following example demonstrates how a GridLayout lays out components with different values for rows, columns, horizontal gap, vertical gap and screen size.

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.EventQueue;
import java.awt.GridLayout;

import javax.swing.BorderFactory;
import javax.swing.Box;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JSpinner;
import javax.swing.SpinnerNumberModel;
import javax.swing.WindowConstants;
import javax.swing.event.ChangeEvent;
import javax.swing.event.ChangeListener;

public class GridLayoutExample {

    private GridLayout gridLayout;
    private JPanel gridPanel, contentPane;
    private JSpinner rowsSpinner, columnsSpinner, hgapSpinner, vgapSpinner;

    public void createAndShowGUI() {
        gridLayout = new GridLayout(5, 5, 3, 3);

        gridPanel = new JPanel(gridLayout);

        final ChangeListener rowsColumnsListener = new ChangeListener() {
            @Override
            public void stateChanged(ChangeEvent e) {
                gridLayout.setRows((int) rowsSpinner.getValue());
                gridLayout.setColumns((int) columnsSpinner.getValue());
                fillGrid();
            }
        };

        final ChangeListener gapListener = new ChangeListener() {
            @Override
            public void stateChanged(ChangeEvent e) {
                gridLayout.setHgap((int) hgapSpinner.getValue());
                gridLayout.setVgap((int) vgapSpinner.getValue());
                gridLayout.layoutContainer(gridPanel);
                contentPane.revalidate();
                contentPane.repaint();
            }
        };

        rowsSpinner = new JSpinner(new SpinnerNumberModel(gridLayout.getRows(), 1, 10, 1));
        rowsSpinner.addChangeListener(rowsColumnsListener);

        columnsSpinner = new JSpinner(new SpinnerNumberModel(gridLayout.getColumns(), 1, 10, 1));
        columnsSpinner.addChangeListener(rowsColumnsListener);

        hgapSpinner = new JSpinner(new SpinnerNumberModel(gridLayout.getHgap(), 0, 50, 1));
        hgapSpinner.addChangeListener(gapListener);

        vgapSpinner = new JSpinner(new SpinnerNumberModel(gridLayout.getVgap(), 0, 50, 1));
        vgapSpinner.addChangeListener(gapListener);

        JPanel actionPanel = new JPanel();
        actionPanel.add(new JLabel("Rows:"));
        actionPanel.add(rowsSpinner);
        actionPanel.add(Box.createHorizontalStrut(10));
        actionPanel.add(new JLabel("Columns:"));
        actionPanel.add(columnsSpinner);
        actionPanel.add(Box.createHorizontalStrut(10));
        actionPanel.add(new JLabel("Horizontal gap:"));
        actionPanel.add(hgapSpinner);
        actionPanel.add(Box.createHorizontalStrut(10));
        actionPanel.add(new JLabel("Vertical gap:"));
        actionPanel.add(vgapSpinner);

        contentPane = new JPanel(new BorderLayout(0, 10));
        contentPane.add(gridPanel);
        contentPane.add(actionPanel, BorderLayout.SOUTH);
        
        fillGrid();

        JFrame frame = new JFrame("GridLayout Example");
        frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        frame.setContentPane(contentPane);
        frame.setSize(640, 480);
        frame.setLocationByPlatform(true);
        frame.setVisible(true);
    }

    private void fillGrid() {
        gridPanel.removeAll();
        for (int row = 0; row < gridLayout.getRows(); row++) {
            for (int col = 0; col < gridLayout.getColumns(); col++) {
                JLabel label = new JLabel("Row: " + row + " Column: " + col);
                label.setHorizontalAlignment(JLabel.CENTER);
                label.setBorder(BorderFactory.createLineBorder(Color.GRAY));
                gridPanel.add(label);
            }
        }
        contentPane.revalidate();
        contentPane.repaint();
    }

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                new GridLayoutExample().createAndShowGUI();
            }
        });
    }

}