java中paint repaint update 之间的关系

2022-07-03 10:46:33

最近总结了一下java中的paint，repaint和updata三者之间的关系，首先咱们都知道用paint方法来绘图，用repaint重绘，用update来写双缓冲。但是他们之间是怎么来调用的呢，咱们来分析一下（想直接看结果，请跳过分析过程）：

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1.首先咱们画在JFrame上面

import java.awt.Color;
import java.awt.Graphics;
import java.awt.Image;
import javax.swing.JFrame;

运行之后的界面

但是你仔细观察一下，会发现有闪烁现象，怎么办呢？我第一时间想到的就是加个双缓冲。那么咱们来试一下！

import java.awt.Color;
import java.awt.Graphics;
import java.awt.Image;
import javax.swing.JFrame;

public class Jframe extends JFrame{
int x = 40,y=50;
Jframe(){
this.setSize(800,700);
this.setLocationRelativeTo(null);
this.getContentPane().setBackground(Color.GREEN);
this.setVisible(true);
this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}
public static void main(String[] args) {
new Jframe();
}
Image offScreenImage = null;
public void update(Graphics g) { //双缓冲
if(offScreenImage == null) {
offScreenImage = this.createImage(800, 600);
}
Graphics gOffScreen = offScreenImage.getGraphics();
Color c = gOffScreen.getColor();
gOffScreen.setColor(Color.GREEN);
gOffScreen.fillRect(0, 0, 800, 600);
gOffScreen.setColor(c);
paint(gOffScreen);
g.drawImage(offScreenImage, 0, 0, null);
}
public void paint(Graphics g){
super.paint(g);
g.setColor(Color.RED);
g.fillOval(x, y, 20, 20);
y++;
repaint();
try {
Thread.sleep(10);
} catch (InterruptedException e) {
// TODO 自动生成的 catch 块
e.printStackTrace();
}
}
}

运行：仔细看一下，发现还是闪烁，这是什么鬼，难道双缓冲加错了么？咱们再用Frame试一下

import java.awt.Color;
import java.awt.Frame;
import java.awt.Graphics;
import java.awt.Image;
import javax.swing.JFrame;

public class Jframe extends Frame{
int x = 40,y=50;
Jframe(){
this.setSize(800,700);
this.setLocationRelativeTo(null);
this.setBackground(Color.GREEN);
this.setVisible(true);
// this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}
public static void main(String[] args) {
new Jframe();
}
Image offScreenImage = null;
public void update(Graphics g) { //双缓冲
if(offScreenImage == null) {
offScreenImage = this.createImage(800, 600);
}
Graphics gOffScreen = offScreenImage.getGraphics();
Color c = gOffScreen.getColor();
gOffScreen.setColor(Color.GREEN);
gOffScreen.fillRect(0, 0, 800, 600);
gOffScreen.setColor(c);
paint(gOffScreen);
g.drawImage(offScreenImage, 0, 0, null);
}
public void paint(Graphics g){
super.paint(g);
g.setColor(Color.RED);
g.fillOval(x, y, 20, 20);
y++;
repaint();
try {
Thread.sleep(10);
} catch (InterruptedException e) {
// TODO 自动生成的 catch 块
e.printStackTrace();
}
}
}

运行：发现不闪烁了，说明刚才加的双缓冲是没有问题的，然后我在JFrame的update方法里和Frame的update方法里都加个输出语句

结果发现，JFrame运行后并没有输出0，而Frame在不断输出0；

看来JFrame压根没有调用update方法！！！

然后咱们用JPanel再试一下，把小球画在JPanel上面

import java.awt.Color;
import java.awt.Graphics;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class Jpanel extends JPanel{
int x=40,y=40;
Jpanel(){
JFrame frame = new JFrame();
frame.setSize( 800, 600);
frame.setLayout(null);
this.setBounds(0, 0, 800, 700);
frame.setLocationRelativeTo(null);
frame.setVisible(true);
this.setBackground(Color.GREEN);
frame.add(this);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}
public static void main(String[] args) {
new Jpanel();
}
public void paint(Graphics g){
super.paint(g);
g.setColor(Color.red);
g.fillOval(x, y, 20, 20);
y++;
repaint();
try {
Thread.sleep(10);
} catch (InterruptedException e) {
// TODO 自动生成的 catch 块
e.printStackTrace();
}
}
}