Simple listener

First, we need to know how to construct an event monitor

1. Create a BtnAction class , Declare after class implements ActionListener

public class BtnAction implements ActionListener{}

2. Override methods in the interface （ Add the code you want in the method ）

public void actionPerformed(ActionEvent e) {
        JFrame jF = new JFrame();
        count++;
        jF.setTitle("" + count);
        jF.setSize(300, 100);
        jF.setVisible(true);
    }

3. Use the button object to call addActionListener Method

  ButtonListener btnaction = new ButtonListener();
        O1.addActionListener(btnaction);

However, the parameter of the method is the object of the class we created ourselves

Mouse monitor

The steps of mouse listener are similar , First, create a class declaration method MouseListener, And then rewrite it MouseListener The method in the method , Load the method you want . In addition, you need to create a listener in the interface

Assign the obtained object to the attribute in the listener .

The following is a drawing image code using a mouse listener

import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import javax.swing.*;
public class DrawListener implements MouseListener {
    int x1,x2,y1,y2;
    Graphics g;
    Graphics p;
    public void mouseClicked(MouseEvent e){
        System.out.println(" Click on ");
    }


    public void mousePressed(MouseEvent e){
        x1 = e.getX();
        y1 = e.getY();

        System.out.println(" Press down ");
    }


    public void mouseReleased(MouseEvent e){
        x2 = e.getX();
        y2 = e.getY();
        System.out.println(" Release ");
        g.drawLine(x1,y1,x2,y2);
        p.drawRect(x1,y1,x2,y2);

        //g.fillOval (x1,y1,30,30);

    }


    public void mouseEntered(MouseEvent e){
        System.out.println(" Get into ");
    }


    public void mouseExited(MouseEvent e){

        System.out.println(" Leave ");
    }
}

The following is the window interface settings

package com.yn.draw0311;
import java.awt.*;
import javax.swing.*;

    public class DrawUI extends JFrame {
        public void initUI() {
            // Because it inherits the class JFrame, So there is no need to create objects 
            this.setTitle(" Graph drawing ");
            this.setSize(500, 800);
            this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            this.setVisible(true);

            //  Create a listener   Add to form object 
            DrawListener dl = new DrawListener();
            // Non button 
            addMouseListener(dl);
            //  obtain Graphics  object   Assign a value to   Properties in the listener g
            Graphics g = getGraphics();
            dl.g = g;
            dl.p=g;
        }
        public static void main(String[] args) {
            DrawUI drawUI = new DrawUI();
            drawUI.initUI();

        }

    }