Java怎么在JPanel里面绘图

可以实现一个Paintable接口

interface Paintable{ public void paint(Graphics g)}

然后在主类上挂一个Paintable的数组，比如private Vector<Paintable>drawings

每鼠标点击一次，就往drawings里面添加一个Paintable对象。

而在主类JPanel的paint中循环依次对drawings中的所有对象进行一次性绘制。

和背景一起绘制也就不多占资源。

也可以外面结合区部重绘repaint(int x, int y, int width, int height)

package draw

import java.awt.*

import java.awt.event.*

import java.awt.geom.*

import java.io.*

import java.util.*

import javax.swing.*

//the point

//impress the info of one point,the x and y

class OnePoint implements Serializable

{

int x

int y

int tool

Color c

int border

public OnePoint(int x,int y,int tool,Color cc,int border)

{

this.x=x

this.y=y

this.tool=tool

this.c=cc

this.border=border

}

public static void main(String[] args)

{

DrawingBoard oneBorder=new DrawingBoard()

}

}

class DrawingBoard extends Frame implements MouseListener,ItemListener,ActionListener,MouseMotionListener

{

Button pen,line,ellipse,rect,clear,colorboard,storebutton,openbutton

Choice sizechoice,colorchoice

Label pensize, pencolor

Panel panel

FileDialog storefile, openfile

FileInputStream filein

FileOutputStream fileout

ObjectInputStream objectin

ObjectOutputStream objectout

int mode=0

int flagtool=0

Color flagcolor

int border

BasicStroke size

private Point2D[] p=new Point2D[3]

OnePoint p1,p2

Vector points=new Vector()

public DrawingBoard()

{

pen=new Button("画笔")

line=new Button("直线")

ellipse=new Button("圆")

rect=new Button("矩形")

clear=new Button("清除")

colorboard=new Button("调色板")

storebutton=new Button("存储文件")

openbutton=new Button("打开文件")

pensize=new Label("画笔大小")

pencolor=new Label("画笔颜色")

storefile=new FileDialog(this,"存储文件",FileDialog.SAVE)

storefile.setVisible(false)

storefile.addWindowListener(new WindowAdapter(){

public void windowClosing(WindowEvent e){

storefile.setVisible(false)

}

})

openfile=new FileDialog(this,"打开文件",FileDialog.LOAD)

openfile.setVisible(false)

openfile.addWindowListener(new WindowAdapter(){

public void windowClosing(WindowEvent e){

openfile.setVisible(false)

}

})

sizechoice=new Choice()

sizechoice.add("1")

sizechoice.add("2")

sizechoice.add("4")

sizechoice.add("6")

sizechoice.add("8")

sizechoice.addItemListener(this)

colorchoice=new Choice()

colorchoice.add("black")

colorchoice.add("red")

colorchoice.add("blue")

colorchoice.add("green")

colorchoice.addItemListener(this)

pen.addActionListener(this)

line.addActionListener(this)

ellipse.addActionListener(this)

rect.addActionListener(this)

clear.addActionListener(this)

colorboard.addActionListener(this)

storebutton.addActionListener(this)

openbutton.addActionListener(this)

panel=new Panel()

panel.add(storebutton)

panel.add(openbutton)

panel.add(pen)

panel.add(line)

panel.add(ellipse)

panel.add(rect)

panel.add(clear)

panel.add(sizechoice)

panel.add(pensize)

panel.add(colorchoice)

panel.add(pencolor)

panel.add(colorboard)

add(panel,BorderLayout.NORTH)

setBounds(100,100,700,600)

setVisible(true)

addWindowListener(new WindowAdapter(){

public void windowClosing(WindowEvent e){

System.exit(0)

}

})

/**

* 添加鼠标事件的监听器，否则，鼠标的移动和点击都将无法识别！

* */

addMouseListener(this)

addMouseMotionListener(this)

}

public void paint(Graphics g)

{

Graphics2D g2d=(Graphics2D)g

if(flagtool==2)

{ //qing chu

g.clearRect(0,0,getSize().width,getSize().height)

}

for(int i=0i<points.size()-1i++)

{

p1=(OnePoint)points.elementAt(i)

p2=(OnePoint)points.elementAt(i+1)

g2d.setColor(p1.c)//////////////需要使用Graphics2D从Graphics类中继承下来的方法 setColor（）设置当前的颜色

size=new BasicStroke(p1.border,BasicStroke.CAP_BUTT,BasicStroke.JOIN_BEVEL)

g2d.setStroke(size)

if(p1.tool==p2.tool)

{

switch(p1.tool)

{

case 0:

Line2D.Double line1=new Line2D.Double(p1.x,p1.y,p2.x,p2.y)

g2d.draw(line1)

break

case 1:

Line2D.Double line2=new Line2D.Double(p1.x,p1.y,p2.x,p2.y)

g2d.draw(line2)

break

case 3:

Ellipse2D.Double ellipse=new Ellipse2D.Double(p1.x,p1.y,Math.abs(p2.x-p1.x),Math.abs(p2.y-p1.y))

g2d.draw(ellipse)

break

case 4:

Rectangle2D.Double rect=new Rectangle2D.Double(p1.x,p1.y,Math.abs(p2.x-p1.x),Math.abs(p2.y-p1.y))

g2d.draw(rect)

break

default:

}

}

}

}

public void mouseClicked(MouseEvent e) {}

public void mouseEntered(MouseEvent e) {}

public void mouseExited(MouseEvent e) {}

public void mousePressed(MouseEvent e) //鼠标点下时候，将当前的点信息记录

{

mode=0

p[0]=e.getPoint()

OnePoint pp1=new OnePoint(e.getX(),e.getY(),flagtool,flagcolor,border)

points.addElement(pp1)

//repaint()

}

public void mouseReleased(MouseEvent e) //鼠标松开时候，如果是画笔，则当前截断，是其余状态记下一枚点信息

{

mode=1

if(flagtool==0)

{

points.addElement(new OnePoint(-1,-1,22,flagcolor,border))

}

else

{

OnePoint pp2=new OnePoint(e.getX(),e.getY(),flagtool,flagcolor,border)

points.addElement(pp2)

points.add(new OnePoint(-1,-1,22,flagcolor,border))

}

repaint()

}

public void itemStateChanged(ItemEvent e)

{

if(e.getSource()==colorchoice)

{

String selected=colorchoice.getSelectedItem()

if(selected=="black"){flagcolor=new Color(0,0,0)}

else if(selected=="red"){flagcolor=new Color(255,0,0)}

else if(selected=="blue"){ flagcolor=new Color(0,0,255)}

else if(selected=="green"){ flagcolor=new Color(0,255,0)}

}

else if(e.getSource()==sizechoice)

{

String selected=sizechoice.getSelectedItem()

if (selected=="1"){ border=1}

else if(selected=="2"){ border=2*2}

else if(selected=="4"){ border=4*2}

else if(selected=="6"){ border=6*2}

else if(selected=="8"){ border=8*2}

}

}

/*public void update(Graphics g) { //@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@

paint(g)

} */

public void actionPerformed(ActionEvent e)

{

// TODO Auto-generated method stub

if(e.getSource()==pen){flagtool=0}

else if(e.getSource()==line){ flagtool=1}

else if(e.getSource()==clear)

{

flagtool=2

points.removeAllElements()

repaint()//此语要有，否则今生无法删除！

}

else if(e.getSource()==ellipse){ flagtool=3}

else if(e.getSource()==rect){ flagtool=4}

else if(e.getSource()==colorboard)

{

/*

* 使用 javax.swing.×包中的 JColorChooser 类的静态方法showDialog（Component component，String title，Color color ），

* 该方法的参数，component是当前显示对话框的父框架，color是设置调色板初始的被选颜色

*

* 该方法返回被选的颜色，类型为Color

* */

Color color=JColorChooser.showDialog(this, "调色板",flagcolor)

flagcolor=color

}

else if(e.getSource()==openbutton)

{

openfile.setVisible(true)

if(openfile.getFile()!=null)

{

int temp=flagtool

flagtool=2

repaint()

try{

points.removeAllElements()

File file=new File(openfile.getDirectory(),openfile.getFile())

filein=new FileInputStream(file)

objectin=new ObjectInputStream(filein)

points=(Vector)objectin.readObject()

objectin.close()

filein.close()

flagtool=temp

repaint()

}

catch(Exception ee){ System.out.println(ee.toString())}

}

}

else if(e.getSource()==storebutton)

{

storefile.setVisible(true)

if(storefile.getFile()!=null)

{

try {

File file=new File(storefile.getDirectory(),storefile.getFile())

fileout=new FileOutputStream(file)

objectout=new ObjectOutputStream(fileout)

objectout.writeObject(points)

objectout.close()

fileout.close()

repaint()

}

catch (FileNotFoundException e1)

{

System.out.println(e1.toString())

e1.printStackTrace()

} catch (IOException ee) {

System.out.println(ee.toString())

ee.printStackTrace()

}

}

}

}

public void mouseDragged(MouseEvent e) //鼠标拖动时候，//当且仅当 flagtool＝＝0，或者表示为橡皮的时候

//才将拖动过程中涉及到的点全部记录下来，并且调用repain()方法，重画当前

// TODO Auto-generated method stub

{

if(flagtool==0)

{

OnePoint pp3=new OnePoint(e.getX(),e.getY(),flagtool,flagcolor,border)

points.addElement(pp3)

repaint()

}

if(flagtool==1)

{

OnePoint pp3=new OnePoint(e.getX(),e.getY(),flagtool,flagcolor,border)

repaint()

}

}

public void mouseMoved(MouseEvent e) {

// TODO Auto-generated method stub

}

}

可以直接把小Panel放到大Panel里啊，如下的例子就是jp2里加了一个jp1

package com.htzy

import javax.swing.*

public class Demo1_1 extends JFrame{

 //变量

 JPanel jp1,jp2

 JTextField jt

 JButton jb

 

 public static void main(String[] args) {

  new Demo1_1()

 }

 

 //构造函数

 public Demo1_1(){

  

  jp1 = new JPanel()

  jp2 = new JPanel()

  jt = new JTextField(10)

  jb = new JButton("确定")

  

  jp1.add(jt)

  jp1.add(jb)

  jp2.add(jp1)//把jp1面板加入到jp2中

  

  this.add(jp2)

  this.setSize(240,200)

  this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE)

  this.setVisible(true)

 }

}

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