Question

java小画板程序该怎么做，大部分教程到最后都没舍得给一个几十行代码的小例子

就是如何用Swing和Java2D做一个小画板，可以完成画图功能中的铅笔和画直线，这样一个小程序就可以了。
大部分教程上面都是一大堆这样方法那样方法乱七八糟的，最后也没舍得给一个画一条直线的例子的完整程序，这样看起来很累。
希望你能帮我完成，谢谢

Answer 1

import java.awt.BorderLayout; //布局管理器的一种，一个面板分东南西北中五个区， 用于放置控间，这样GUI在放大缩小，移植的时候方便
import java.awt.Button;
import java.awt.Color;
import java.awt.Container;// 一般的 Abstract Window Toolkit(AWT) 容器对象是一个可包含其他 AWT 组件的组件
import java.awt.Graphics; //定义一个真正的工具,用来接受图形操作
import java.awt.Panel; // Panel 是最简单的容器类
import java.awt.event.ActionEvent; //知道如何对自身进行指派的事件的接口
import java.awt.event.ActionListener; //用于接收操作事件的侦听器接口
import java.awt.event.MouseAdapter; //接收鼠标事件的抽象适配器类
import java.awt.event.MouseEvent; //鼠标事件
import java.awt.event.MouseListener; //用于接收组件上“感兴趣”的鼠标事件（按下、释放、单击、进入或离开）的侦听器接口。
import java.awt.event.MouseMotionAdapter; //接收鼠标移动事件的适配器
import java.awt.event.MouseMotionListener; //用于接收组件上的鼠标移动事件的侦听器接口
import javax.swing.ButtonGroup; //此类用于为一组按钮创建一个多斥（multiple-exclusion）作用域
import javax.swing.JFrame; //java.awt.Frame 的扩展版本，该版本添加了对 JFC/Swing 组件架构的支持
import javax.swing.JPanel; JPanel //是一般轻量级容器
import javax.swing.UIManager; //此类跟踪当前的外观及其默认设置
//import javax.swing.Component; //对数据和方法的简单封装
Public class ShapeMain extends JFrame implements ActionListener,MouseListener,MouseMotionListener{
int x,y,x1,y1,x2,y2,width,height;
boolean isFirstPoint = true;
//初始化开始画的是线
int drawType = PaintingGround.LINE;
//初始化开始不是填充
boolean isFill = false;
//添加控件
ButtonGroup btg = new ButtonGroup();
Button btLine = new Button("线");
Button btRectangle = new Button("矩形");
Button btRound = new Button("圆");
Button btEllipse = new Button("椭圆");
Button tbFillState = new Button("填充");
Button button3 = new Button("文本操作");
Button button2 = new Button("清除");
Button button1 = new Button("选择颜色");
Panel buttonPanel = new Panel();
PaintingGround paintingGround = new PaintingGround();
//Main Method
public static void main(String[] args) {
//设置显示外观
try{
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
}catch(Exception e) {
e.printStackTrace();
}
new ShapeMain();
}
//构造函数
public ShapeMain() {
//控件添加到控件组中
// btg.add(btLine);
// btg.add(btRectangle);
// btg.add(btRound);
// btg.add(btEllipse);
buttonPanel.add(btLine);
buttonPanel.add(btRectangle);
buttonPanel.add(btRound);
buttonPanel.add(btEllipse);
buttonPanel.add(tbFillState);
//设置容器及容器的整体布局
Container cp = this;
cp.setLayout(new BorderLayout());
cp.add(BorderLayout.NORTH,buttonPanel);
cp.add(BorderLayout.CENTER,paintingGround);
//cp.add(BorderLayout.SOUTH,jf);
//jf.setJMenuBar(mb);
setLocation(300,150);
setSize(600,480);
setVisible(true);
setDefaultCloseOperation(EXIT_ON_CLOSE);
//添加鼠标触发事件
paintingGround.addMouseListener(new MouseAdapter() {
public void mouseReleased(MouseEvent evn) {
isFirstPoint = true;
} });
//对鼠标的输入进行判断并调用画图程序
paintingGround.addMouseMotionListener(new MouseMotionAdapter() {
public void mouseDragged(MouseEvent evn) {
if(isFirstPoint) {
x1 = evn.getX();
y1 = evn.getY();
isFirstPoint = false;
}
else {
x2 = evn.getX();
y2 = evn.getY();
switch(drawType) {
case PaintingGround.LINE:
//画线
paintingGround.drawLine(x1,y1,x2,y2);
break;
case PaintingGround.RECTANGLE:
//画矫形
paintingGround.drawRect(x1,y1,x2-x1,y2-y1);
break;
case PaintingGround.ROUND:
//画圆
//两点距离公式
int size = Math.abs((int)Math.sqrt((x2-x1)*(x2-x1) + (y2-y1)*(y2-y1)));
paintingGround.drawRound(x1,y1,size);
break;
case PaintingGround.ELLIPSE:
//画椭圆
paintingGround.drawEllipse(x1,y1,x2-x1,y2-y1);
break;
default:
break;
}}}});
//各个控件的触发事件
btLine.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent evn) {
drawType = PaintingGround.LINE;
}});
btRectangle.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent evn) {
drawType = PaintingGround.RECTANGLE;
}});
btRound.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent evn) {
drawType = PaintingGround.ROUND;
}});
btEllipse.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent evn) {
drawType = PaintingGround.ELLIPSE;
}});
tbFillState.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent evn) {
isFill = tbFillState.isShowing();
paintingGround.setFillState(isFill);
}});}
public void actionPerformed(ActionEvent e) {
// TODO Auto-generated method stub
}
public void mouseClicked(MouseEvent e) {
// TODO Auto-generated method stub
}
public void mousePressed(MouseEvent e) {
// TODO Auto-generated method stub
}
public void mouseReleased(MouseEvent e) {
// TODO Auto-generated method stub
}
public void mouseEntered(MouseEvent e) {
// TODO Auto-generated method stub
}
public void mouseExited(MouseEvent e) {
// TODO Auto-generated method stub
}
public void mouseDragged(MouseEvent e) {
// TODO Auto-generated method stub
}
public void mouseMoved(MouseEvent e) {
// TODO Auto-generated method stub
} }
class PaintingGround extends JPanel {
public static final int LINE = 1;
public static final int RECTANGLE = 2;
public static final int ROUND = 3;
public static final int ELLIPSE = 4;
private int x,y;
private int x1,y1,x2,y2;
private int width, height,size;
private int drawType = 0;
private boolean isFill = false;
//构造函数
public PaintingGround() {
setBackground(Color.black);
}
//判断是用实心还是空心的,
public void paint(Graphics g) {
super.paint(g);
g.setColor(Color.white);
if(isFill) {
switch(drawType) {
case LINE:
g.drawLine(x1,y1,x2,y2);
break;
case RECTANGLE:
g.fillRect(x,y,width,height);
break;
case ROUND:
g.fillOval(x,y,size,size);
break;
case ELLIPSE:
g.fillOval(x,y,width,height);
break;
default:
break;
}}
else {
switch(drawType) {
case LINE:
g.drawLine(x1,y1,x2,y2);
break;
case RECTANGLE:
g.drawRect(x,y,width,height);
break;
case ROUND:
g.drawOval(x,y,size,size);
break;
case ELLIPSE:
g.drawOval(x,y,width,height);
break;
default:
break;
} } }
public void drawLine(int x1, int y1, int x2,int y2) {
this.x1 = x1;
this.y1 = y1;
this.x2 = x2;
this.y2 = y2;
drawType = LINE;
repaint();
}
//具体的实现方式
public void drawRect(int x,int y,int width, int height) {
this.x = x;
this.y = y;
this.width = width;
this.height = height;
drawType = RECTANGLE;
repaint();
}
public void drawRound(int x,int y,int size) {
this.x = x;
this.y = y;
this.size = size;
drawType = ROUND;
repaint();
}
public void drawEllipse(int x,int y,int width,int height) {
this.x = x;
this.y = y;
this.width = width;
this.height = height;
drawType = ELLIPSE;
repaint();
}
public void setFillState(boolean isFill) {
this.isFill = isFill;
} }

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Answer 2

官方的指南上很多例子，不用看别的，就《Java turtorial》就足够

追问

这就是答案？

追答

如果看完java指南你还没解决问题，你在追问呗！