不知道为什么public void mousePressed(MouseEvent e)会执行两次

package mywuziqi;

//import javax.swing.*;

//import javax.swing.*;

//import javax.swing.*;

import javax.imageio.ImageIO;
import javax.swing.*;
import java.awt.*;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;

public class mychessjframe extends JFrame implements MouseListener {
    int x = 0;
    int y = 0;
    //0表示没有棋子 1表示黑子 2表示白子
    int[][] allchess = new int[21][21];
    boolean is = false;
    // 取得桌面的宽高
//    int width = Toolkit.getDefaultToolkit().getScreenSize().width;
//    int height = Toolkit.getDefaultToolkit().getScreenSize().height;

    public mychessjframe() {
        this.setTitle("五子棋");                      //窗口标题
        this.setSize(500, 500);         //画布大小
//        this.setLocation(width-500/2,height-500/2);
        this.setLocationRelativeTo(null);          //居中
        this.setResizable(false);                  //窗口大小不可变
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        this.addMouseListener(this);
        this.addMouseListener(this);
        this.setVisible(true);                    //窗口显示
    }

    public void paint(Graphics g) {

        BufferedImage image = null;
        try {
            image = ImageIO.read(new File("D:/pic/bg.jpg"));
        } catch (IOException e) {
            e.printStackTrace();
        }
        g.drawImage(image, 0, 0, this);
        g.setFont(new Font("黑体", 40, 40));
        g.drawString("游戏信息", 10, 70);
        g.setFont(new Font("宋体", 0, 15));
        g.drawString("黑方时间：无限制", 10, 480);
        g.drawString("白方时间：无限制", 250, 480);
        for (int i = 0; i < 21; i++) {
            g.drawLine(10, 100 + i * 15, 310, 100 + i * 15);
            g.drawLine(10 + i * 15, 100, 10 + i * 15, 400);
        }
//        g.fillOval(96, 160, 5, 5);
//        g.fillOval(360, 160, 5, 5);
//        g.fillOval(96, 339, 5, 5);
//        g.fillOval(360, 340, 5, 5);

//        g.fillOval(x,y,12,12);
//        allchess[1][1]=1;
//        g.fillOval(10+30-5,100+30-5,10,10);
        for (int i = 0; i < 21; i++) {
            for (int j = 0; j < 21; j++) {
                //如果等于1画黑旗
                if (allchess[i][j] == 1) {
                    int tempx = i * 15 + 10;
                    int tempy = j * 15 + 100;
                    g.fillOval(tempx - 5, tempy - 5, 10, 10);

                }
                //如果等于2画白棋
                if (allchess[i][j] == 2) {
                    int tempx = i * 15 + 10;
                    int tempy = j * 15 + 100;
                    g.setColor(Color.white);
                    g.fillOval(tempx - 5, tempy - 5, 10, 10);
                    g.setColor(Color.black);
                    g.drawOval(tempx - 5, tempy - 5, 10, 10);

                }
            }
        }

    }


    @Override
    public void mouseClicked(MouseEvent e) {

    }

    @Override
    public void mousePressed(MouseEvent e) {
        x = e.getX();
        y = e.getY();
//        System.out.println(x);
//        System.out.println(y);
        if (x > 10 && x < 450 && y > 100 && y < 400) {
            x = (x - 10) / 15;
            y = (y - 100) / 15;
            if (is) {
                allchess[x][y] = 1;
                is = false;
                System.out.println("执行了if");
            }
            else {
                allchess[x][y] = 2;
                is = true;
                System.out.println("执行了else");
            }
//            allchess[x][y]=1;
            this.repaint();
        }
        else  {
            System.out.println("鼠标位置超出棋盘");
        }


    }

    @Override
    public void mouseReleased(MouseEvent e) {

    }

    @Override
    public void mouseEntered(MouseEvent e) {

    }

    @Override
    public void mouseExited(MouseEvent e) {

    }
}