用java写一个简易画图板

目标是实现一个简单的画板，可以通过点击上方的按钮改变要画的形状，颜色。大致效果如下图

一、画图板界面实现

所需用到的主要API类：JFrame，JButton，FlowLayout，Graphics以及一些相关的类；

先创建窗体，设置相关属性，再添加按钮。

import java.awt.Color;
import java.awt.Dimension;
import java.awt.FlowLayout;
import java.awt.Graphics;
import java.awt.Graphics2D;

import javax.swing.JButton;
import javax.swing.JFrame;

public class Draw extends JFrame{

public static void main(String args[]){
Draw dr = new Draw();
dr.showdraw();
}
public void showdraw(){
//继承后JFrame后无需实例化
this.setTitle("画图板");
this.setSize(700,500);
//frame.setResizable(false);
this.setDefaultCloseOperation(3);
this.setLocationRelativeTo(null);
FlowLayout f1 = new FlowLayout();
this.setLayout(f1);
        //实例化监听器
DrawListener lis = new DrawListener();
//创建图形按钮和颜色按钮
String[] array ={"Line","Pencil","Rect","Oval","RoundRect","fillRect",
"fillArc","fillOval","Text","Image","Triangle","Polygon"};
for(int i=0 ; i JButton button = new JButton(array[i]);
this.add(button);
button.addActionListener(lis);
}
Color[] colorArray ={Color.black,Color.blue,
Color.green,Color.red};
for(int i=0 ; i JButton button = new JButton();
button.setBackground(colorArray[i]);
button.setPreferredSize(new Dimension(30,30));//设置按钮大小
this.add(button);
button.addActionListener(lis);
}
this.setVisible(true);  //setVisible设置窗体可见，放在所有组件后

Graphics g = this.getGraphics();
this.addMouseListener(lis);//用this指代frame可能出错
this.addMouseMotionListener(lis);

lis.setG(g);

}

二、监听类的实现

所需用到的主要API类：MouseAdapter，BasicStroke，Color，Graphics，JButton以及相关的类。以及ActionListener接口

监听按钮上对应的图形或颜色，并根据得到的内容实现对应的操作，具体的画图在Shape类中实现

import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Image;
import java.awt.RenderingHints;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;

import javax.swing.ImageIcon;
import javax.swing.JButton;

//先继承类，后继承接口
public class DrawListener extends MouseAdapter implements ActionListener{

private int x1, y1, x2, y2,x3,y3,sx,sy,ex,ey;
private Graphics2D g2;
private String str = "Line";
private Color color;
private int flag = 1;//用于标记是否是第一次画线

public void setG(Graphics g){
g2 = (Graphics2D) g;
g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
RenderingHints.VALUE_ANTIALIAS_ON);// 设置画笔开启抗锯齿

}

public void actionPerformed(ActionEvent e){

JButton button = (JButton) e.getSource();//getSource返回事件源类型，也可以用getActionCommand返回String类型

if(button.getText() != "")//如果为图形按钮

str = button.getText();

else{
color = button.getBackground();
System.out.println("color"+color);
}
}

public void mouseClicked(MouseEvent e){
System.out.println("点击");//按下和释放要在同一位置才是点击
x2 = e.getX();
            y2 = e.getY();
   
    //画空心矩形
    if(str.equals("Rect")){
    Shape s = new Shape(x2,y2,80,40,color,
new BasicStroke(1),"Rect");
    s.draw(g2);
    }
    //画填充矩形
    if(str.equals("fillRect")){
    Shape s = new Shape(x2,y2,80,40,color,
new BasicStroke(1),"fillRect");
    s.draw(g2);
    }
    //画圆角矩形
    if(str.equals("RoundRect")){
    Shape s = new Shape(x2,y2,80,40,color,
new BasicStroke(1),"fillRect");
    s.draw(g2);
    }
    //画空心圆
    if(str.equals("Oval")){
    Shape s = new Shape(x2,y2,80,40,color,
new BasicStroke(1),"Oval");
    s.draw(g2);
    }
    //画填充圆
    if(str.equals("fillOval")){
    Shape s = new Shape(x2,y2,80,40,color,
new BasicStroke(1),"fillOval");
    s.draw(g2);
    }
    //画填充弧
    if(str.equals("fillArc")){
    Shape s = new Shape(x2,y2,80,80,color,
new BasicStroke(1),"fillArc");
    s.draw(g2);
    }
    //画图片
    if(str.equals("Image")){
    //先用ImageIcon设置路径，再获取图片(绝对路径)
    ImageIcon icon = new ImageIcon("C:\\Users\\lenovo\\Desktop\\background1.jpg");
    Image img = icon.getImage();
    Shape s = new Shape(x2,y2,200,150,
img,"Image");
    s.draw(g2);
    }
    //画文本
    if(str.equals("Text")){
    String text = "Hello World";
    Font font = new Font("华文行楷", Font.BOLD + Font.ITALIC, 26);//字体，粗体，斜体，大小
    g2.setFont(font);
    Shape s = new Shape(x2,y2,text,"Text");
    s.draw(g2);
    }
    //画任意多边形
    if(str.equals("Polygon")){
    if(flag == 2){
    Shape s = new Shape(ex,ey,x2,y2,color,
    new BasicStroke(1),"Line");
    s.draw(g2);
    ex = x2;
    ey = y2;
    }
    //如果与起点较近或鼠标双击，则闭合多边形
    if((Math.abs(sx-x2)<10 && Math.abs(sy-y2)<10)
    ||(e.getClickCount()==2)){
    Shape s = new Shape(sx,sy,x2,y2,color,
    new BasicStroke(1),"Line");
    s.draw(g2);
    flag = 1;
    }
    }
   }

    public void mousePressed(MouseEvent e){
    x1 = e.getX();
    y1 = e.getY();
    g2.setColor(color);
    if(flag == 1){
    sx = x1;
    sy = y1;
    }
    }

    public void mouseReleased(MouseEvent e){
    x2 = e.getX();
    y2 = e.getY();
   
    //画直线
    if(str.equals("Line")){
    Shape s = new Shape(x1,y1,x2,y2,color,
    new BasicStroke(1),"Line");
    s.draw(g2);
    }
    //画任意多边形
    if(str.equals("Polygon")){
    if(flag == 1){
    Shape s = new Shape(x1,y1,x2,y2,color,
    new BasicStroke(1),"Line");
    s.draw(g2);
    ex = x2;
    ey = y2;
    flag = 2;
    }
    }
    //画等腰三角形
    if(str.equals("Triangle")){
    Shape s = new Shape(x1,y1,x2,y2,color,
new BasicStroke(1),"Triangle");
    s.draw(g2);
    }
    }

    public void mouseDragged(MouseEvent e){
    x3 = e.getX();
    y3 = e.getY();
   
    //画曲线
    if(str.equals("Pencil")){
    Shape s = new Shape(x1, y1, x3, y3, color,
    new BasicStroke(10),"Pencil");
    s.draw(g2);
   
    x1 = x3;
    y1 = y3;
    }
    }

}

三、实现画图形的Shape类

需要定义多个构造方法，传递不同图形需要的参数值，再进行绘制

import java.awt.Color;
import java.awt.Graphics2D;
import java.awt.Image;
import java.awt.Stroke;

public class Shape {
public int x1,x2,y1,y2;
public Stroke stroke;
public Color color;
public String type;
public Image img;
public String text;

public Shape(int x1,int y1,int x2,int y2,Color color,
Stroke stroke,String type){
this.x1=x1;
this.y1=y1;
this.x2=x2;
this.y2=y2;
this.color=color;
this.stroke=stroke;
this.type=type;
}

public Shape(int x1,int y1,int x2,int y2,
Image img,String type){
this.x1=x1;
this.y1=y1;
this.x2=x2;
this.y2=y2;
this.img=img;
this.type=type;
}

public Shape(int x1,int y1,
String text,String type){
this.x1=x1;
this.y1=y1;
this.text=text;
this.type=type;
}

public void draw(Graphics2D g){

if(type.equals("Line") || type.equals("Pencil")){
g.setColor(color);
g.setStroke(stroke);
g.drawLine(x1, y1, x2, y2);
}
else if(type.equals("Image")){
g.drawImage(img,x1,y1,x2,y2,null);
}
else if(type.equals("Rect")){
g.setColor(color);
g.setStroke(stroke);
g.drawRect(x1, y1, x2, y2);
}
else if(type.equals("Oval")){
g.setColor(color);
g.setStroke(stroke);
g.drawOval(x1, y1, x2, y2);
}
else if(type.equals("fillRect")){
g.setColor(color);
g.setStroke(stroke);
g.fillRect(x1, y1, x2, y2);
}
else if(type.equals("RoundRect")){
g.setColor(color);
g.setStroke(stroke);
g.drawRoundRect(x1, y1, x2, y2, 10, 10);
}
else if(type.equals("fillOval")){
g.setColor(color);
g.setStroke(stroke);
g.fillOval(x1, y1, x2, y2);
}
else if(type.equals("fillArc")){
g.setColor(color);
g.setStroke(stroke);
g.fillArc(x1, y1, x2, y2,0,-90);
}
else if(type.equals("Text")){
g.drawString(text, x1, y1);
}
else if(type.equals("Triangle")){
g.setColor(color);
g.setStroke(stroke);
g.drawLine(x1,y1,x2,y2);
    g.drawLine(2*x1-x2, y2, x2, y2);
    g.drawLine(x1,y1,2*x1-x2, y2);
}
}
}

四、画图板的重绘

在实现以上类后，已经可以实现点击对应按钮，画出对应的图形和颜色，但是一旦窗体改变，画的图形就会消失。这是因为图形没有被储存，一旦窗体改变后就生成了一个新窗体，旧的图形不会在新窗体上显示,因此需要保存图形数据，并在新窗体上重绘。

//draw类

        lis.setArray(shapeArray);//增加对图形数组的监听

public Shape[] shapeArray = new Shape[1000];//储存图形的数组
public void paint(Graphics g){
super.paint(g);//super为父类
System.out.println("绘制了");
Graphics2D g2 = (Graphics2D) g;
for(int i=0 ; i Shape s = shapeArray[i];
if(s != null)
s.draw(g2);
}

}

//drawListener类，增加图形数组，并收集数据

        private Shape[] array;

private int index=0;

        public void setArray(Shape[] array){
this.array = array;
}

        //以画空心矩形为例
    if(str.equals("Rect")){
    Shape s = new Shape(x2,y2,80,40,color,
new BasicStroke(1),"Rect");
    s.draw(g2);
    if(index<1000)
    array[index++] = s;
    }