Question

java程序设计时在JFrame中要清除一个圆再画一个矩形该怎么清除？

Answer 1

import java.awt.*;
import java.awt.event.*;
import java.awt.geom.Point2D;
import java.awt.image.BufferedImage;
import javax.swing.*;
import javax.swing.border.Border;
public class DrawShapes extends JFrame{
private static final long serialVersionUID = 3685715844170953607L;
//Graphic panel
private CVS cvs;
//作图方式选择按钮
private JToggleButton cycle,line,rect;
private JLabel red,blue,green;
private ButtonGroup bgroup;
//按钮布局面板
private JPanel menuPanel;
//复位按钮
private JButton clean;
public DrawShapes(){
super("Java 实训");
// this.setResizable(false);
this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
this.setSize(640,480);
this.setLocationRelativeTo(null);
this.getContentPane().add(cvs=new CVS());
this.initComponents();
}
//初始化组件
private void initComponents() {
this.menuPanel = new JPanel(null);
this.menuPanel.setPreferredSize(new Dimension(400,28));
this.menuPanel.setBorder(BorderFactory.createLineBorder(Color.gray));
this.getContentPane().add(this.menuPanel,"South");
this.bgroup = new ButtonGroup();
this.cycle = new JToggleButton("圆形");
this.cycle.setBounds(20,4,68,20);
this.line = new JToggleButton("直线");
this.line.setBounds(100,4,68,20);
this.rect=new JToggleButton("矩形");
this.rect.setBounds(180,4,68,20);
red = new JLabel();
red.setOpaque(true);
red.setBackground(Color.red);
red.setBounds(258,4,20,20);
blue=new JLabel();
blue.setOpaque(true);
blue.setBackground(Color.blue);
blue.setBounds(282,4,20,20);
green=new JLabel();
green.setBackground(Color.green);
green.setOpaque(true);
green.setBounds(306,4,20,20);
this.menuPanel.add(red);
this.menuPanel.add(blue);
this.menuPanel.add(green);
this.menuPanel.add(cycle);
this.menuPanel.add(line);
this.menuPanel.add(rect);
this.bgroup.add(cycle);
this.bgroup.add(line);
this.bgroup.add(rect);
this.clean = new JButton("清除");
this.clean.setBounds(338,4,68,20);
this.menuPanel.add(clean);
//按钮动作侦听器实例
ActionListener al = new ActionListener(){
public void actionPerformed(ActionEvent e) {
Object src = e.getSource();
if(src.equals(cycle))
cvs.setSX(S.CYCLE);//画圆
else if(src.equals(line))
cvs.setSX(S.LINE);//画直线
else if(src.equals(rect))
cvs.setSX(S.RECTANGLE);//画矩形
else if(src.equals(clean))
cvs.reset();//复位
}
};
//给按钮注册侦听器
this.cycle.addActionListener(al);
this.line.addActionListener(al);
this.rect.addActionListener(al);
this.clean.addActionListener(al);
MouseListener ml = new MouseAdapter(){
public void mousePressed(MouseEvent e){
Object s = e.getSource();
Border b = BorderFactory.createLoweredBevelBorder();
if(s.equals(red)){
cvs.setFC(Color.red);
red.setBorder(b);
blue.setBorder(null);
green.setBorder(null);
}
else if(s.equals(blue)){
cvs.setFC(Color.blue);
blue.setBorder(b);
red.setBorder(null);
green.setBorder(null);
}
else if(s.equals(green)){
cvs.setFC(Color.green);
green.setBorder(b);
blue.setBorder(null);
red.setBorder(null);
}
}
};
blue.addMouseListener(ml);
red.addMouseListener(ml);
green.addMouseListener(ml);
}
//程序入口
public static void main(String[] aregs) throws Exception{
//调用系统视觉设置
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
SwingUtilities.invokeLater(new Runnable(){
public void run(){
new DrawShapes().setVisible(true);
}
});
}
}
//主作图面板类,可接收一般鼠标事件和鼠标拖动事件
class CVS extends Canvas implements MouseListener,MouseMotionListener{
private static final long serialVersionUID = 5585026114112579483L;
//指定图形的第一点,比如矩形的角点,圆形的圆心,直线的第一点
private int x,y;
//作图大小
private int w,h;
//作图类型控制
private S sx = S.NULL;
//双缓冲,背景缓冲区和临时缓冲区
private BufferedImage background,buff;
//图像更新标记
private boolean hasChanged;
//背景色,临时作图色,前景色
private Color bgc = Color.white;
private Color tmpc = Color.gray;
private Color fgc = Color.blue;
public CVS(){
this.addMouseListener(this);
this.addMouseMotionListener(this);
}
//作图控制方式设置
public void setSX(S s){
sx = s;
}
//控制作图颜色:
public void setFC(Color c){
fgc=c;
}
//绘制临时缓冲区
private void drawing(int X,int Y) {
Graphics g = buff.getGraphics();
g.setColor(bgc);
g.clearRect(0,0,w,h);
copyBuffer();
g.setColor(tmpc);
switch(sx){
case CYCLE:
Point p = new Point(x,y);
Point2D p2 = new Point2D.Double(X,Y);
int dist = (int)p.distance(p2);
g.drawOval(x,y,0,0);
g.drawOval(x-dist, y-dist,dist*2,dist*2);
break;
case LINE:
g.drawLine(x,y,X,Y);
break;
case RECTANGLE:
int dx = x-X;
dx = Math.abs(dx);
int dy = y-Y;
dy = Math.abs(dy);
g.drawRect(x<X?x:X,y<Y?y:Y,dx,dy);
break;
}
g.dispose();
drawBufferToCVS();
}
//绘制背景缓冲区
private void drawBuffer(int X,int Y){
Graphics2D gd = background.createGraphics();
gd.setColor(fgc);
gd.setRenderingHint(RenderingHints.KEY_ANTIALIASING,RenderingHints.VALUE_ANTIALIAS_ON);
switch(sx){
case CYCLE:
Point p = new Point(x,y);
Point2D p2 = new Point2D.Double(X,Y);
int dist = (int)p.distance(p2);
gd.drawOval(x,y,0,0);
gd.drawOval(x-dist, y-dist,dist*2,dist*2);
break;
case LINE:
gd.drawLine(x,y,X,Y);
break;
case RECTANGLE:
int dx = x-X;
dx = Math.abs(dx);
int dy = y-Y;
dy = Math.abs(dy);
gd.drawRect(x<X?x:X,y<Y?y:Y,dx,dy);
break;
default:
popupMsg();
}
gd.dispose();
Graphics g = this.getGraphics();
g.clearRect(0,0,w,h);
g.drawImage(background,0,0,null);
g.dispose();
}
private void popupMsg(){
JOptionPane.showMessageDialog(this,"请选择一种作图方式开始作图.");
}
//复制背景缓冲区内容到临时缓冲区
private void copyBuffer(){
Graphics g = buff.getGraphics();
g.drawImage(background,0,0,null);
g.dispose();
}
//印出临时缓冲区内容到窗口
private void drawBufferToCVS() {
Graphics g = this.getGraphics();
g.drawImage(buff,0,0,null);
g.dispose();
}
//清除双缓冲区并清除窗口内容
public void reset(){
clearContents(buff);
clearContents(background);
Graphics g = this.getGraphics();
g.setColor(bgc);
g.fillRect(0,0,w,h);
g.dispose();
}
//清除指定缓冲区内容
private void clearContents(BufferedImage i){
Graphics g = i.getGraphics();
g.setColor(bgc);
g.fillRect(0,0,w,h);
g.dispose();
}
//初始化缓冲区
private void initImages() {
background=new BufferedImage(w,h,BufferedImage.TYPE_INT_RGB);
buff=new BufferedImage(w,h,BufferedImage.TYPE_INT_RGB);
clearContents(background);
clearContents(buff);
}
//重写此方法,以便在窗口重新显示时能正确显示最后的内容.
public void paint(Graphics g){
// w = this.getWidth();
// h = this.getHeight();
if(background==null){
w = this.getToolkit().getScreenSize().width;
h = this.getToolkit().getScreenSize().height;
initImages();
}
g.drawImage(background,0,0,null);
g.dispose();
}
//双击作图区也能做清除动作,呵呵
public void mouseClicked(MouseEvent e) {
if(e.getClickCount()==2)
reset();
}
public void mouseEntered(MouseEvent e) {}
public void mouseExited(MouseEvent e) {}
//每当按下鼠标时就重新设置第一点的坐标
public void mousePressed(MouseEvent e) {
this.x=e.getX();
this.y=e.getY();
}
//每当释放鼠标时就决定是否需要将背景缓冲区印出到窗口
public void mouseReleased(MouseEvent e) {
if(hasChanged){
hasChanged=false;
drawBuffer(e.getX(),e.getY());
}
}
//每当鼠标拖动时开始作图
public void mouseDragged(MouseEvent e) {
hasChanged=true;
drawing(e.getX(),e.getY());
}
public void mouseMoved(MouseEvent e) {}
}
//作图类型的枚举
enum S{
CYCLE,RECTANGLE,LINE,NULL
}

Answer 2

Graphics g = this.getGraphics();
g.setColor(bgc);
g.fillRect(0,0,w,h);

清屏

Answer 3

JFrame frame=new JFrame();
frame.remove(圆)；
frame.paint(矩形);
frame.repaint();

Answer 4

removeAll()?