Question

我正在编写一个程序，当点击鼠标时，将绘制一个圆圈。到目前为止我写的下面的代码。

import java.awt.*;
import javax.swing.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import javax.swing.event.*;
import java.awt.geom.*;

public class test extends JFrame implements ActionListener, MouseListener {
    Shape circle = new Ellipse2D.Float(10, 10, 10, 10);

    public test () {
        setSize(250,150);
        addMouseListener(this);
    }

    public static void main(String[] args) {
        //TODO code application logic here
        java.awt.EventQueue.invokeLater(new Runnable() {
              public void run() {
                   test frame = new test();
                   frame.setVisible(true);
              }
        });
    }

    public void actionPerformed(ActionEvent ae) {

    }

    public void drawCircle(int x, int y) {
        Graphics g = this.getGraphics();
        g.drawOval(x, y, x, y);
        g.setColor(Color.BLACK);
        g.fillOval(x, y, 2, 2);
    }

    public void mouseClicked(MouseEvent e) {
        drawCircle(e.getX(), e.getY());
        repaint();
    }

    public void mouseExited(MouseEvent e) {

    }

    public void mousePressed(MouseEvent e) {

    }

    public void mouseReleased(MouseEvent e) {

    }

    public void mouseEntered(MouseEvent e) {

    }
}

代码是一个400X400的jframe，当点击打开时显示一个半圈的圆圈，问题是，当我释放鼠标时，圆圈消失。为什么呢？

Answer 1

将您的mouseClick(...)更改为：

int x, y;

public void mouseClicked(MouseEvent e) {
    x = e.getX();
    y = e.getY();

    repaint();
}

覆盖paint(...)：

@Override
public void paint(Graphics g) {
    drawCircle(x, y);
}

Answer 2

当您致电repaint()时，该组件会从头开始重新绘制。你的圈子被抹去了。您将希望覆盖每次绘制组件时调用的paintComponent(Graphics)。

当鼠标点击时，java绘制一个圆圈

2 个答案: