How do I display a jPanel when I place my mouse over a certain region?

Question

Hello, I would like to know how to create an algorithm in Java to display a certain Panel within my Form Jframe, as soon as the user positions the mouse cursor on a certain pre-programmed region, which will be a specific corner of the Form Jframe itself!

Answer 1

Does this help you? Explanation in the code comments.

import java.awt.Color;
import java.awt.Container;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import javax.swing.JFrame;
import javax.swing.JPanel;

/**
 * @author Victor
 */
public class MouseTest {
    public static void main(String[] args) {
        EventQueue.invokeLater(MouseTest::seguir);
    }

    private static void seguir() {
        // 1. Cria a JFrame.
        JFrame tela = new JFrame("Isto é uma tela");
        tela.setResizable(true);
        tela.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);

        // 2. Cria a JPanel que irá aparecer. Desenha algo dentro dele para ficar bem visível.
        JPanel panel = new JPanel() {
            @Override
            public void paintComponent(Graphics g) {
                Graphics2D g2 = (Graphics2D) g;
                g2.setColor(Color.BLUE);
                g2.fillRect(0, 0, this.getWidth(), this.getHeight());
                g2.setColor(Color.YELLOW);
                char[] t = "Olá, eu sou o JPanel!".toCharArray();
                g2.drawChars(t, 0, t.length, 30, 10);
            }
        };
        panel.setPreferredSize(new Dimension(300, 30));
        tela.add(panel);
        panel.setVisible(false); // Inicialmente invisível.

        // 3. Faz com que ao passar o mouse perto do canto inferior direito da tela, a JPanel apareça.
        // O segredo é adionar um MouseMotionListener.
        Container content = tela.getContentPane();
        tela.addMouseMotionListener(new MouseAdapter() {
            @Override
            public void mouseMoved(MouseEvent e) {
                if (e.getX() > content.getWidth() * 0.9 && e.getY() > content.getHeight() * 0.9) panel.setVisible(true);
            }
        });

        // 4. Mostra a tela.
        tela.setMinimumSize(new Dimension(300, 300));
        tela.pack();
        tela.setVisible(true);
    }
}

Made with java 8.

Answer 2

This effect you seek to achieve is easier to implement using Javafx because in it you can use CSS at the front-end. No CSS just use the property hover which is super easy and you don’t have to use Java code.