如何使用鼠标拖动事件在java小程序上绘制矩形并使其保持不变

我有一个可以画矩形的程序。我有两个问题无法解决。在我画出矩形后，它不会停留。我所拥有的唯一一个清除“UnderPaint，repaint”中画布的代码仅在鼠标拖动时调用。为什么当我释放鼠标或移动鼠标时，画布会清晰。第二件事并没有那么大的问题，但我搞不清楚，当我的矩形的高度或宽度为负数时，矩形用黑色填充

package pracpapp2;


import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class MouseTracker4July extends JFrame
   implements MouseListener, MouseMotionListener {


  private static final long serialVersionUID = 1L;
  private JLabel mousePosition;
  int x, y;
  int x1, x2, y1, y2;
  int w, h;
  private JLabel recStart;
  private JLabel recStop;
  private JLabel cords;
   // set up GUI and register mouse event handlers
   public MouseTracker4July()
   {
      super( "Rectangle Drawer" );

      mousePosition = new JLabel();
      mousePosition.setHorizontalAlignment(SwingConstants.CENTER);
      getContentPane().add( mousePosition, BorderLayout.CENTER );


      JLabel text1 = new JLabel();
      text1.setText( "At the center the mouse pointer's coordinates will be displayed." );
      getContentPane().add( text1, BorderLayout.SOUTH );

      recStart = new JLabel();
      getContentPane().add(recStart, BorderLayout.WEST);

      recStop = new JLabel();
      getContentPane().add(recStop, BorderLayout.EAST);

      cords = new JLabel();
      getContentPane().add(cords, BorderLayout.NORTH);


      addMouseListener( this );        // listens for own mouse and
      addMouseMotionListener( this );  // mouse-motion events

      setSize( 800, 600 );
      setVisible( true );
   }

   // MouseListener event handlers
   // handle event when mouse released immediately after press
   public void mouseClicked( MouseEvent event )
   {
      mousePosition.setText( "Clicked at [" + event.getX() +
         ", " + event.getY() + "]" );
   }

   // handle event when mouse pressed
   public void mousePressed( MouseEvent event )
   {

      mousePosition.setText( "Pressed at [" +(x1 = event.getX()) +
         ", " + (y1 = event.getY()) + "]" );

      recStart.setText( "Start:  [" + x1 +
         ", " + y1 + "]" );
   }

   // handle event when mouse released after dragging
   public void mouseReleased( MouseEvent event )
   {
     mousePosition.setText( "Released at [" +(x2 = event.getX()) +
         ", " + (y2 = event.getY()) + "]" );

     recStop.setText( "End:  [" + x2 +
         ", " + y2 + "]" );

   }

   // handle event when mouse enters area
   public void mouseEntered( MouseEvent event )
   {
      mousePosition.setText( "Mouse entered at [" + event.getX() +
         ", " + event.getY() + "]" );
   }

   // handle event when mouse exits area
   public void mouseExited( MouseEvent event )
   {
      mousePosition.setText( "Mouse outside window" );
   }

   // MouseMotionListener event handlers
   // handle event when user drags mouse with button pressed
   public void mouseDragged( MouseEvent event )
   {
      mousePosition.setText( "Dragged at [" + (x = event.getX()) + 
         ", " + (y = event.getY()) + "]" );
      // call repaint which calls paint
      repaint();

   }

   // handle event when user moves mouse
   public void mouseMoved( MouseEvent event )
   {
      mousePosition.setText( "Moved at [" + event.getX() +
         ", " + event.getY() + "]" );
   }

   public void paint(Graphics g)
   {
      super.paint(g); // clear the frame surface
      g.drawString("Start Rec Here", x1, y1);
      g.drawString("End Rec Here", x, y);

      w = x1 - x;
      h = y1 - y;
      w = w * -1;
      h = h * -1;

      g.drawRect(x1, y1, w, h);

      cords.setText( "w = " + w + ", h = " + h);
   }

   public static void main( String args[] )
   { 
      MouseTracker4July application = new MouseTracker4July();
      application.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
   }

} // end class MouseTracker

---

您需要将绘制的项目存储在某些数据结构中，并确保在重新绘制时将结构中的每个项目绘制到画布上

此外，您还需要为每个鼠标事件添加重绘

这样：（假设您想要保留所有的rect）-您可以通过删除arraylist并替换为单个rect实例来使用单个rect

import java.awt.BorderLayout;
import java.awt.Graphics;
import java.awt.Rectangle;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.event.MouseMotionListener;
import java.util.ArrayList;

import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.SwingConstants;

public class MouseTracker4July extends JFrame implements MouseListener, MouseMotionListener {

    private static final long serialVersionUID = 1L;
    private final JLabel mousePosition;
    int x1, x2, y1, y2;
    int w, h;
    private final JLabel recStart;
    private final JLabel recStop;
    private final JLabel cords; // set up GUI and register mouse event handlers
    private final ArrayList< Rectangle > rectangles = new ArrayList< Rectangle >();
    private boolean isNewRect = true;

    public MouseTracker4July() {
        super( "Rectangle Drawer" );

        this.mousePosition = new JLabel();
        this.mousePosition.setHorizontalAlignment( SwingConstants.CENTER );
        getContentPane().add( this.mousePosition, BorderLayout.CENTER );

        JLabel text1 = new JLabel();
        text1.setText( "At the center the mouse pointer's coordinates will be displayed." );
        getContentPane().add( text1, BorderLayout.SOUTH );

        this.recStart = new JLabel();
        getContentPane().add( this.recStart, BorderLayout.WEST );

        this.recStop = new JLabel();
        getContentPane().add( this.recStop, BorderLayout.EAST );

        this.cords = new JLabel();
        getContentPane().add( this.cords, BorderLayout.NORTH );

        addMouseListener( this ); // listens for own mouse and
        addMouseMotionListener( this ); // mouse-motion events

        setSize( 800, 600 );
        setVisible( true );

    }

// MouseListener event handlers // handle event when mouse released immediately after press 
    public void mouseClicked( final MouseEvent event ) {
        this.mousePosition.setText( "Clicked at [" + event.getX() + ", " + event.getY() + "]" );

        repaint();
    }

// handle event when mouse pressed 
    public void mousePressed( final MouseEvent event ) {

        this.mousePosition.setText( "Pressed at [" + ( this.x1 = event.getX() ) + ", " + ( this.y1 = event.getY() ) + "]" );

        this.recStart.setText( "Start:  [" + this.x1 + ", " + this.y1 + "]" );

        repaint();
    }

// handle event when mouse released after dragging 
    public void mouseReleased( final MouseEvent event ) {
        this.mousePosition.setText( "Released at [" + ( this.x2 = event.getX() ) + ", " + ( this.y2 = event.getY() ) + "]" );

        this.recStop.setText( "End:  [" + this.x2 + ", " + this.y2 + "]" );

        Rectangle rectangle = getRectangleFromPoints();

        this.rectangles.add( rectangle );

        this.w = this.h = this.x1 = this.y1 = this.x2 = this.y2 = 0;
        this.isNewRect = true;

        repaint();
    }

    private Rectangle getRectangleFromPoints() {
        int width = this.x1 - this.x2;
        int height = this.y1 - this.y2;
        Rectangle rectangle = new Rectangle( width < 0 ? this.x1
            : this.x2, height < 0 ? this.y1
            : this.y2, Math.abs( width ), Math.abs( height ) );

        return rectangle;
    }

// handle event when mouse enters area 
    public void mouseEntered( final MouseEvent event ) {
        this.mousePosition.setText( "Mouse entered at [" + event.getX() + ", " + event.getY() + "]" );
        repaint();
    }

// handle event when mouse exits area 
    public void mouseExited( final MouseEvent event ) {
        this.mousePosition.setText( "Mouse outside window" );
        repaint();
    }

// MouseMotionListener event handlers // handle event when user drags mouse with button pressed 
    public void mouseDragged( final MouseEvent event ) {
        this.mousePosition.setText( "Dragged at [" + ( this.x2 = event.getX() ) + ", " + ( this.y2 = event.getY() ) + "]" ); // call repaint which calls paint repaint();

        this.isNewRect = false;

        repaint();
    }

// handle event when user moves mouse 
    public void mouseMoved( final MouseEvent event ) {
        this.mousePosition.setText( "Moved at [" + event.getX() + ", " + event.getY() + "]" );
        repaint();
    }

    @Override
    public void paint( final Graphics g ) {
        super.paint( g ); // clear the frame surface 
        g.drawString( "Start Rec Here", this.x1, this.y1 );
        g.drawString( "End Rec Here", this.x2, this.y2 );

        Rectangle newRectangle = getRectangleFromPoints();
        if ( !this.isNewRect ) {
            g.drawRect( newRectangle.x, newRectangle.y, newRectangle.width, newRectangle.height );
        }

        for( Rectangle rectangle : this.rectangles ) {
            g.drawRect( rectangle.x, rectangle.y, rectangle.width, rectangle.height );
        }

        this.cords.setText( "w = " + this.w + ", h = " + this.h );

    }

    public static void main( final String args[] ) {
        MouseTracker4July application = new MouseTracker4July();
        application.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
    }

} // end class MouseTracker

导入java.awt.BorderLayout；
导入java.awt.Graphics；
导入java.awt.Rectangle；
导入java.awt.event.MouseEvent；
导入java.awt.event.MouseListener；
导入java.awt.event.MouseMotionListener；
导入java.util.ArrayList；
导入javax.swing.JFrame；
导入javax.swing.JLabel；
导入javax.swing.SwingConstants；
公共类MouseTracker4July扩展JFrame实现MouseListener、MouseMotionListener{
私有静态最终长serialVersionUID=1L；
私人最终JLabel鼠标位置；
int-x1，x2，y1，y2；
int w，h；
私人最终JLabel重新启动；
私人最终JLabel recStop；
专用最终JLabel跳线；//设置GUI并注册鼠标事件处理程序
私有最终ArrayList<矩形>矩形=新ArrayList<矩形>（）；
私有布尔值isNewRect=true；
公共捕鼠器7月4日（）{
超级（“矩形抽屉”）；
this.mousePosition=new JLabel（）；
此.mousePosition.setHorizontalAlignment（SwingConstants.CENTER）；
getContentPane（）.add（this.mousePosition，BorderLayout.CENTER）；
JLabel text1=新的JLabel（）；
text1.setText（“将在鼠标指针的中心显示坐标”）；
getContentPane（）.add（text1，BorderLayout.SOUTH）；
this.recStart=new JLabel（）；
getContentPane（）.add（this.recStart，BorderLayout.WEST）；
this.recStop=new JLabel（）；
getContentPane（）.add（this.recStop，BorderLayout.EAST）；
this.cords=新的JLabel（）；
getContentPane（）.add（this.cords，BorderLayout.NORTH）；
addMouseListener（此）；//侦听自己的鼠标和
addMouseMotionListener（this）；//鼠标运动事件
设置大小（800600）；
setVisible（真）；
}
//MouseListener事件处理程序//在按下鼠标后立即释放鼠标时处理事件
公共无效鼠标点击（最终鼠标事件）{
this.mousePosition.setText（“单击[“+event.getX（）+”，“+event.getY（）+”]）；
重新油漆（）；
}
//按下鼠标时处理事件
公共无效鼠标按下（最终鼠标事件）{
this.mousePosition.setText（“在[”+（this.x1=event.getX（））+，“+（this.y1=event.getY（））+”）处按下”；
this.recStart.setText（“Start:[“+this.x1+”，“+this.y1+”]）；
重新油漆（）；
}
//拖动鼠标后释放鼠标时处理事件
公共无效MouseEvent事件（最终MouseEvent事件）{
this.mousePosition.setText（“在[”+（this.x2=event.getX（））+“，”+（this.y2=event.getY（））+“]时发布”；
this.recStop.setText（“End:[“+this.x2+”，“+this.y2+”]）；
矩形矩形=getRectangleFromPoints（）；
这个.rectangles.add（矩形）；
this.w=this.h=this.x1=this.y1=this.x2=this.y2=0；
this.isNewRect=true；
重新油漆（）；
}
私有矩形getRectangleFromPoints（）{
int width=this.x1-this.x2；
内部高度=this.y1-this.y2；
矩形矩形=新矩形（宽度<0？此值为0.x1
：this.x2，高度<0？this.y1
：this.y2，Math.abs（宽度），Math.abs（高度）；
返回矩形；
}
//鼠标进入区域时处理事件
公共无效鼠标事件（最终鼠标事件）{
this.mousePosition.setText（“鼠标输入于[“+event.getX（）+”，“+event.getY（）+”]）；
重新油漆（）；
}
//鼠标退出区域时处理事件
公共无效mouseExited（最终MouseEvent事件）{
this.mousePosition.setText（“鼠标在窗口外”）；
重新油漆（）；
}
//MouseMotionListener事件处理程序//在用户拖动鼠标并按下按钮时处理事件
公共无效鼠标标记（最终鼠标事件）{
this.mousePosition.setText（“在[”+（this.x2=event.getX（））+，“+（this.y2=event.getY（））+”）处拖动；//调用repaint，调用paint repaint（）；
this.isNewRect=false；
重新油漆（）；
}
//当用户移动鼠标时处理事件
public void mouseMoved（最终MouseEvent事件）{
this.mousePosition.setText（“在[“+event.getX（）+”，“+event.getY（）+”]）处移动；
重新油漆（）；
}
@凌驾
公共空间油漆（最终图形g）{
super.paint（g）；//清除框架表面
g、 抽绳（“此处开始记录”，this.x1，this.y1）；
g、 抽绳（“此处末端Rec”，this.x2，this.y2）；
矩形newRectangle=getRectangleFromPoints（）；
如果（！this.isNewRect）{
g、 drawRect（newRectangle.x，newRectangle.y，newRectangle.width，newRectangle.height）；
}
用于（矩形：this.rectangles）{
g、 drawRect（矩形.x，矩形.y，矩形.width，矩形.height）；
}
this.cords.setText（“w=“+this.w+”，h=“+this.h”）；
}
公共静态void main（最终字符串参数[]）{
MouseTracker4July应用程序=新的MouseTracker4July（）；
application.setDefaultCloseOperation（JFrame.EXIT_ON_CLOSE）；
}
}//结束c
import java.awt.BorderLayout;
import java.awt.Graphics;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.event.MouseMotionListener;

import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.SwingConstants;

public class MouseTracker4July extends JFrame implements MouseListener, MouseMotionListener {

    private static final long serialVersionUID = 1L;
    private final JLabel mousePosition;
    int x1, x2, y1, y2;
    int x, y, w, h;
    private final JLabel recStart;
    private final JLabel recStop;
    private final JLabel cords; // set up GUI and register mouse event handlers
    boolean isNewRect = true;

    public MouseTracker4July() {
        super( "Rectangle Drawer" );

        this.mousePosition = new JLabel();
        this.mousePosition.setHorizontalAlignment( SwingConstants.CENTER );
        getContentPane().add( this.mousePosition, BorderLayout.CENTER );

        JLabel text1 = new JLabel();
        text1.setText( "At the center the mouse pointer's coordinates will be displayed." );
        getContentPane().add( text1, BorderLayout.SOUTH );

        this.recStart = new JLabel();
        getContentPane().add( this.recStart, BorderLayout.WEST );

        this.recStop = new JLabel();
        getContentPane().add( this.recStop, BorderLayout.EAST );

        this.cords = new JLabel();
        getContentPane().add( this.cords, BorderLayout.NORTH );

        addMouseListener( this ); // listens for own mouse and
        addMouseMotionListener( this ); // mouse-motion events

        setSize( 800, 600 );
        setVisible( true );

    }

// MouseListener event handlers // handle event when mouse released immediately after press 
    public void mouseClicked( final MouseEvent event ) {
        this.mousePosition.setText( "Clicked at [" + event.getX() + ", " + event.getY() + "]" );

        repaint();
    }

// handle event when mouse pressed 
    public void mousePressed( final MouseEvent event ) {

        this.mousePosition.setText( "Pressed at [" + ( this.x1 = event.getX() ) + ", " + ( this.y1 = event.getY() ) + "]" );

        this.recStart.setText( "Start:  [" + this.x1 + ", " + this.y1 + "]" );

        this.isNewRect = true;

        repaint();
    }

// handle event when mouse released after dragging 
    public void mouseReleased( final MouseEvent event ) {
        this.mousePosition.setText( "Released at [" + ( this.x2 = event.getX() ) + ", " + ( this.y2 = event.getY() ) + "]" );

        this.recStop.setText( "End:  [" + this.x2 + ", " + this.y2 + "]" );

        repaint();
    }

// handle event when mouse enters area 
    public void mouseEntered( final MouseEvent event ) {
        this.mousePosition.setText( "Mouse entered at [" + event.getX() + ", " + event.getY() + "]" );
        repaint();
    }

// handle event when mouse exits area 
    public void mouseExited( final MouseEvent event ) {
        this.mousePosition.setText( "Mouse outside window" );
        repaint();
    }

// MouseMotionListener event handlers // handle event when user drags mouse with button pressed 
    public void mouseDragged( final MouseEvent event ) {
        this.mousePosition.setText( "Dragged at [" + ( this.x2 = event.getX() ) + ", " + ( this.y2 = event.getY() ) + "]" ); // call repaint which calls paint repaint();

        this.isNewRect = false;

        repaint();
    }

// handle event when user moves mouse 
    public void mouseMoved( final MouseEvent event ) {
        this.mousePosition.setText( "Moved at [" + event.getX() + ", " + event.getY() + "]" );
        repaint();
    }

    @Override
    public void paint( final Graphics g ) {
        super.paint( g ); // clear the frame surface 
        g.drawString( "Start Rec Here", this.x1, this.y1 );
        g.drawString( "End Rec Here", this.x2, this.y2 );

        int width = this.x1 - this.x2;
        int height = this.y1 - this.y2;

        this.w = Math.abs( width );
        this.h = Math.abs( height );
        this.x = width < 0 ? this.x1
            : this.x2;
        this.y = height < 0 ? this.y1
            : this.y2;

        if ( !this.isNewRect ) {
            g.drawRect( this.x, this.y, this.w, this.h );
        }

        this.cords.setText( "w = " + this.w + ", h = " + this.h );

    }

    public static void main( final String args[] ) {
        MouseTracker4July application = new MouseTracker4July();
        application.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
    }

} // end class MouseTracker

        public void mouseDragged(MouseEvent event) {
//      mousePosition.setText("Dragged at [" + (x = event.getX()) + ", "
//              + (y = event.getY()) + "]");
        // call repaint which calls paint
        x = event.getX();
        y = event.getY();

        compRectPos();
        repaint();
    }

    private void compRectPos()
    {
        rx = x1;
        ry = y1;

        w = x - x1;
        h = y - y1;

        if ( w < 0)
            rx += w;
        if (h < 0)
            ry += h;

        w = Math.abs(w);
        h = Math.abs(h);

    }

    public void paint(Graphics g) {
        super.paint(g); // clear the frame surface
        g.drawString("Start Rec Here", x1, y1);
        g.drawString("End Rec Here", x, y);

        g.drawRect(rx, ry, w, h);

        cords.setText("w = " + w + ", h = " + h);
    }