如何在Java中绘制矩形时防止刷新

Question

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;  
import java.util.List;
import java.util.ArrayList;
class DrawningBoard extends Canvas implements MouseMotionListener{
private List<Point> points = new ArrayList<>();
private List<List<Point>> curves = new ArrayList<>();
private boolean isRectangle = false;
private int xr, yr, widthr, heightr;
public void setIsRectangle(boolean trueOrFalse){
isRectangle = trueOrFalse;
}
public boolean getIsRectangle(){
return isRectangle;
}
public DrawningBoard(){
setBackground(Color.MAGENTA);
addMouseMotionListener(this); 
addMouseListener(new MouseAdapter(){
public void mouseReleased(MouseEvent e){
curves.add(points);
points = new ArrayList<>();
}
public void mousePressed(MouseEvent e){
points.add(new Point(e.getX(), e.getY()));
}
});
}
public void paint(Graphics g){
g.setColor(Color.CYAN);
if(isRectangle){
g.drawRect(xr, yr, widthr, heightr);
}
for(List<Point> curve : curves){
for(int i = 0; i < curve.size() - 1; i++){
g.drawLine((int)curve.get(i).getX(), (int)curve.get(i).getY(), (int)curve.get(i + 1).getX(), (int)curve.get(i + 1).getY());
}
}
}
public void mouseDragged(MouseEvent e){  
Graphics g = getGraphics();
g.setColor(Color.CYAN);

int xx = e.getX();
int yy = e.getY();

int x = (int)points.get(points.size() - 1).getX();
int y = (int)points.get(points.size() - 1).getY();
int dx = xx-x;
int dy = yy-y;
if(isRectangle){
if(dx >= 0 && dy >= 0){
xr = x;
yr = y;
widthr = dx;
heightr = dy;
} else if(dx < 0 && dy < 0){
xr = xx;
yr = yy;
widthr = -dx;
heightr = -dy;
} else if(dx >= 0 && dy < 0){
xr = x;
yr = yy;
widthr = dx;
heightr = -dy;
} else if(dx < 0 && dy >= 0){
xr = xx;
yr = y;
widthr = -dx;
heightr = dy;
}
repaint();
} 
else {
g.drawLine(xx, yy, (int)points.get(points.size() - 1).getX(), (int)points.get(points.size() - 1).getY());
points.add(new Point(xx, yy));
}

}
public void mouseMoved(MouseEvent e) { }  
}
class GUI extends JFrame implements ActionListener{
private JPanel[] panel;
private JButton[] button;
private DrawningBoard board;
public GUI(String title){
super(title);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);  
setSize(416, 400);

board = new DrawningBoard();
board.setBounds(0,0, 400, 400);

panel = new JPanel[3];
panel[0] = new JPanel();
panel[1] = new JPanel();
panel[2] = new JPanel();
panel[0].setLayout(null);
panel[1].setLayout(null);
panel[2].setLayout(null);
panel[0].setBounds(0, 0, 400, 20);
panel[1].setBounds(0, 20, 400, 400);
panel[2].add(panel[0]);
panel[2].add(panel[1]);
panel[0].setBackground(Color.red);

button = new JButton[5];
button[0] = new JButton("Rectangle");
button[1] = new JButton("b1");
button[2] = new JButton("b2");
button[3] = new JButton("b3");
button[4] = new JButton("b4");
button[0].addActionListener(this);
button[3].addActionListener(this);
button[0].setBounds(0, 0, 100, 20);
button[1].setBounds(100, 0, 100, 20);
button[2].setBounds(200, 0, 100, 20);
button[3].setBounds(300, 0, 100, 20);
button[4].setBounds(0, 0, 100, 20);

panel[0].add(button[0]);
panel[0].add(button[1]);
panel[0].add(button[2]);
panel[0].add(button[3]);
panel[0].add(button[4]);

panel[1].add(board);
add(panel[2]);  

show();
}
public void actionPerformed(ActionEvent e){
String command = e.getActionCommand();
if(command.equals("Rectangle")) 
board.setIsRectangle(!board.getIsRectangle());
}
}

public class Paint{
public static void main(String []str){
new GUI("Paint");
}
}

我想创建一个Paint应用程序。如果我在板上画了多条曲线，然后我想画一个
矩形(使用drawRect(x, y, width, height)(，那么这些曲线将被重新绘制，并由于使用repaint()方法而导致一些冲洗。我该如何避免脸红？
我试着使用update()方法，但鼠标拖动时会画出许多矩形。

Answer 1

Swing在默认情况下是双缓冲的。

public void paint(Graphics g){

不要覆盖paint((。您这样做不正确，并且失去了双重缓冲的好处。

相反，应该通过重写paintComponent(...)方法来完成自定义绘制。阅读Swing教程中关于自定义绘制的部分，了解更多信息和工作示例。

您也可以从Custom Painting Approaches中查看DrawOnComponent示例，以获得一个更完整的示例，满足您的需求。