java图形重绘

为什么需要方法重绘？因为窗体改变的时候会刷新，会把所有的绘制图形给覆盖了，图形重绘可以保存图形，并且把图形在刷新的时候再绘制出来。

直线以及各种图形如何保存？
以面向对象的思维看待图形
图形：直线矩形圆：
属性：图形名坐标颜色 ...
方法：绘制方法

在什么时候绘制出来？
        窗体刷新的时候绘制
        继承Jframe 重写paint方法
        在paint方法中将监听器图形数组中保存好的图形对象遍历取出调用绘制方法

接下来我们讲具体实现方法：

1像之前学的一样创建一个类

public class DrawUI extends Jframe {

    public void showDrawUI(){
        Jframe jf = new Jframe ;
        jf.setTitle("图形重绘");
        jf.setSize(800,800);
        jf.setDefaultCloseOperation(Jframe.EXIT_ON_CLOSE);
        jf.setVisible(true);
    }

    public static void main(String[] args) {
        DrawUI drawui = new DrawUI();
        drawui.showDrawUI();
    }
}

2.创建鼠标监听器，传入画笔，这样方便之后绘制

public class DrawListener implements MouseListener{
    int x1, y1, x2, y2;
    Graphics g;// 需要给Graphics 传递一个画笔对象

    @Override
    public void mouseClicked(MouseEvent e){
    }

    @Override
    public void mousePressed(MouseEvent e){
        x1 = e.getX ();
        y1 = e.getY ();
    }

    
    @Override
    public void mouseReleased(MouseEvent e){
        x2 = e.getX ();
        y2 = e.getY ();
        g.drawLine (x1,y1,x2,y2);  //绘制一条直线
    }

    @Override
    public void mouseEntered(MouseEvent e){
    }

    @Override
    public void mouseExited(MouseEvent e){
    }
}

3.给窗体添加鼠标监听器

public class DrawUI extends Jframe {

    public void showDrawUI(){
        Jframe jf = new Jframe ;
        jf.setTitle("图形重绘");
        jf.setSize(800,800);
        jf.setDefaultCloseOperation(Jframe.EXIT_ON_CLOSE);
        jf.setVisible(true);

        DrawListener dr = new DrawListener();// 给窗体添加鼠标监听器
        jf.addMouseListener(dr);

        //传入画笔
        Graphics g = jf.getGraphics;
        dr.g = g;// 传给监听器对象中的画笔 g
    }

    public static void main(String[] args) {
        DrawUI drawui = new DrawUI();
        drawui.showDrawUI();
    }
}

4.前面讲到直线以及各种图形如何保存？：以面向对象的思维看待图形

所以我们要单独建立一个Shape类来让图形绘画出来，类中一定有方法和属性。

public class Shape{
    String typename;//属性
    int x1,y1,x2,y2;
    Color color;

    public void drawShape(Graphics g){//方法
        g.setColor (color);
        if(typename.equals ("直线")){
            g.drawLine (x1,y1,x2,y2);
        }else if(typename.equals ("矩形")){
            g.drawRect (Math.min (x1,x2),Math.min (y1,y2),Math.abs (x2-x1),Math.abs (y2-y1));
        }else if(typename.equals ("圆")){
            g.drawOval (Math.min (x1,x2),Math.min (y1,y2),Math.abs (x2-x1),Math.abs (y2-y1));
        }else if(typename.equals("实心圆")){
            g.fillOval(Math.min(x1,x2),Math.min(y1,y2),Math.abs(x1-x2),Math.abs(y1-y2));
        }else if(typename.equals("实心矩形")){
            g.fillRect(Math.min(x1,x2),Math.min(y1,y2),Math.abs(x1-x2),Math.abs(y1-y2));
        }
        }
     public static void main(String[] args) {
    }
}

5.如何将Shape和前面连接起来呢？、

要在监听器中创建Shape对象:

// Shape 对象创建
Shape shape = new Shape ();
shape.typename="矩形";
shape.color=Color.RED;
shape.x1=x1;
shape.y1=y1;
shape.x2=x2;
shape.y2=y2;

// 绘制图形调用的是图形的绘制方法
shape.drawShape (g);

因为要画很多次图形，所以应该用数组把他们保存起来：

Shape[] shapeList = new Shape[100];
int shapeindex=0;

// 将每次绘制的图形对象保存至数组中
shapeList[shapeindex++]=shape;
System.out.println ("已经保存了"+shapeindex+"个图形！！");

import java.awt.*;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;

public class DrawListener implements MouseListener{
    int x1, y1, x2, y2;
    Graphics g;// 需要给Graphics 传递一个画笔对象

    @Override
    public void mouseClicked(MouseEvent e){
    }

    @Override
    public void mousePressed(MouseEvent e){
        x1 = e.getX ();
        y1 = e.getY ();
    }

    Shape[] shapeList = new Shape[100];
    int shapeindex=0;//记录链表下标

    @Override
    public void mouseReleased(MouseEvent e){
        x2 = e.getX ();
        y2 = e.getY ();
//        g.drawLine (x1,y1,x2,y2);
        // Shape 对象创建
        Shape shape = new Shape ();
        shape.typename="矩形";
        shape.color=Color.RED;
        shape.x1=x1;
        shape.y1=y1;
        shape.x2=x2;
        shape.y2=y2;

        // 绘制图形 调用的是图形的绘制方法
        shape.drawShape (g);
        // 将每次绘制的图形对象保存至数组中
        shapeList[shapeindex++]=shape;
        System.out.println ("已经保存了"+shapeindex+"个图形！！");
    }

    @Override
    public void mouseEntered(MouseEvent e){

    }

    @Override
    public void mouseExited(MouseEvent e){
    }
}

6. 重写界面的刷新方法，重写的方法会被子类以及子类对象优先调用

前面有讲到：窗体刷新的时候绘制，继承Jframe 重写paint方法，在paint方法中将监听器图形数组中保存好的图形对象遍历取出，调用绘制方法。

具体操作如下：

public void paint(Graphics g){
super.paint (g);
// 从监听器中拿到存储图形的数组
// dl.shapeList;
for(int i = 0; i < dl.shapeIndex; i++){
Shape shape = dl.shapeList[i];
shape.drawShape (g);
}

}

public class DrawUI extends  Jframe{ //extends：用于DrawUI继承Jframe的关键字
    DrawListener dr = new DrawListener (); 
                            //将创建的监听器放到最外面是为了方便下面的所以类都可以调用它
    public void showUI(){
//        Jframe jf = new Jframe; 
            //因为继承了Jframe所以只用写this就行，下面的jf也可以用this来代替
        Jframe jf = this;
        jf.setTitle ("图形图像绘制");
        jf.setSize (800,800);
        jf.setDefaultCloseOperation (Jframe.EXIT_ON_CLOSE);
        jf.setVisible (true);

        jf.addMouseListener (dr);// 给窗体添加鼠标监听器
        Graphics g = jf.getGraphics ();
        dr.g=g;// 传给监听器对象中的画笔 g

    }

    // 重写界面的刷新方法

    
    @Override
    public void paint(Graphics g){
        super.paint (g);
        // 从监听器中拿到存储图形的数组
       // dr.shapeList;
        for(int i = 0; i < dr.shapeindex; i++){
            Shape shape = dr.shapeList[i];
            shape.drawShape (g);
        }
    }

    public static void main(String[] args){
        DrawUI drawui = new DrawUI ();
        drawui.showUI ();
    }
}

已经了解了最基本的方法那么接下来我们完成如何添加按钮，进行颜色选择，并且绘制出想要的图案

1.首先，要加入在窗体中加入按钮监听器和鼠标监听器，这样才能实现功能：

FlowLayout fl = new FlowLayout();
jf.setLayout(fl);

JButton btn = new JButton();
jf.add(btn);
btn.addActionListener(null);

DrawListener dr = new DrawListener();

jf.addMouseListener(dr);
Graphics g = jf.getGraphics();
dr.g = g;

但由于我们有许多的按钮，所以可以考虑用数组的方法来存储建立，并且用封装的思想来依次建立监听器，使代码更加简洁，方法如下：

//建立按钮所需的数组
String[] strs = {"直线", "圆", "矩形", "实心圆", "实心矩形"};
Color[] color ={Color.WHITE,Color.BLACK,Color.yellow,Color.magenta,Color.DARK_GRAY};

//封装好可重复调用的直线

FlowLayout fl = new FlowLayout();
    jf.setLayout(fl);
   
    for(int i=0;i

完整代码如下：

package lyq220104图形重绘;

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

public class DrawUI extends Jframe {

    String[] strs = {"直线", "圆", "矩形", "实心圆", "实心矩形"};
    Color[] color = {Color.WHITE,Color.BLACK,Color.yellow,Color.magenta,Color.DARK_GRAY};
    DrawListener dr = new DrawListener();//放到最前面，这样就可以让showDrawUI和Paint函数都能用到他们
    public void showDrawUI(){
        Jframe jf = this ;
        this.setTitle("图形重绘");
        this.setSize(800,800);
        jf.setDefaultCloseOperation(Jframe.EXIT_ON_CLOSE);
        jf.setVisible(true);

        FlowLayout fl = new FlowLayout();
        jf.setLayout(fl);

        for(int i=0;i 
2.既然窗体已经建立好，那么监听器部分的代码我们也要进行修改 
 
 //implements作为接口连接鼠标监听器和按钮监听器
public class DrawListener implements MouseListener, ActionListener  
 
 
 public void actionPerformed(ActionEvent e) {
    System.out.println("按钮被点击");
    String str = e.getActionCommand(); 
                                //例如 JButton aButton = new JButton("Today");
                                    // getActionCommand（）可以获取到Today
                                    // getSource()获取到的是aButton

    if (str.equals("")){
        System.out.println("这是一个颜色按钮");
        //获取点击的对象 按钮
        JButton jb = (JButton) e.getSource();
        //获取按钮背景颜色
        color = jb.getBackground();
        //设置给画笔对象
        g.setColor(color);
    }else{
        //如果不是空格 那就把字符存入typeStr
        typeStr = str;
    }
} 
 
 
 //初始化
int x1,x2,y1,y2;
Graphics g;
Color color = Color.black;
String typeStr ="直线"; 
 
 
 Shape[] shapeList = new Shape[100];
int shapeindex = 0;
@Override
public void mouseReleased(MouseEvent e) {
    x2 = e.getX();
    y2 = e.getY();
    Shape shape = new Shape ();
    shape.setshapeData(typeStr,x1,x2,y1,y2,color);
    // 绘制图形 调用的是图形的绘制方法
    shape.drawshape(g);
    // 将每次绘制的图形对象保存至数组中
    shapeList[shapeindex++] = shape;
    System.out.println("已经保存了"+shapeindex+"个图形");
} 
 
完整代码如下： 
package lyq220104图形重绘;

import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;

public class DrawListener implements MouseListener, ActionListener {
    int x1,x2,y1,y2;
    Graphics g;
    Color color = Color.black;
    String typeStr ="直线";

    @Override
    public void actionPerformed(ActionEvent e) {
        System.out.println("按钮被点击");
        String str = e.getActionCommand(); //例如 JButton aButton = new JButton("Today");
                                            // getActionCommand（）可以获取到Today
                                            // getSource()获取到的是aButton

        if (str.equals("")){
            System.out.println("这是一个颜色按钮");
            //获取点击的对象 按钮
            JButton jb = (JButton) e.getSource();
            //获取按钮背景颜色
            color = jb.getBackground();
            //设置给画笔对象
            g.setColor(color);
        }else{
            //如果不是空格 那就把字符存入typeStr
            typeStr = str;
        }
    }
    @Override
    public void mouseClicked(MouseEvent e) {

    }

    @Override
    public void mousePressed(MouseEvent e) {
        x1 = e.getX();
        y1 = e.getY();
    }

    Shape[] shapeList = new Shape[100];
    int shapeindex = 0;
    @Override
    public void mouseReleased(MouseEvent e) {
        x2 = e.getX();
        y2 = e.getY();
        Shape shape = new Shape ();
        shape.setshapeData(typeStr,x1,x2,y1,y2,color);
        // 绘制图形 调用的是图形的绘制方法
        shape.drawshape(g);
        // 将每次绘制的图形对象保存至数组中
        shapeList[shapeindex++] = shape;
        System.out.println("已经保存了"+shapeindex+"个图形");
    }

    @Override
    public void mouseEntered(MouseEvent e) {

    }

    @Override
    public void mouseExited(MouseEvent e) {

    }

}
 
3.那么Shape中也需要设置图形数据，才能连接成功，完整代码如下： 
package lyq220104图形重绘;

import java.awt.*;

public class Shape {
    String typename;
    int x1,x2,y1,y2;
    Color color;

    //设置图形数据
    public void setshapeData(String typename, int x1, int x2, int y1, int y2, Color color) {
        this.typename = typename;
        this.x1 = x1;
        this.x2 = x2;
        this.y1 = y1;
        this.y2 = y2;
        this.color = color;
    }

    public void drawshape(Graphics g){
        if(typename.equals("直线")){
            g.drawLine(x1,y1,x2,y2);
        }else if(typename.equals("矩形")){
            g.drawRect(Math.min(x1,x2),Math.min(y1,y2),Math.abs(x1-x2),Math.abs(y1-y2));
        }else if(typename.equals("圆")){
            g.drawOval(Math.min(x1,x2),Math.min(y1,y2),Math.abs(x1-x2),Math.abs(y1-y2));
        }else if(typename.equals("实心圆")){
            g.fillOval(Math.min(x1,x2),Math.min(y1,y2),Math.abs(x1-x2),Math.abs(y1-y2));
        }else if(typename.equals("实心矩形")){
            g.fillRect(Math.min(x1,x2),Math.min(y1,y2),Math.abs(x1-x2),Math.abs(y1-y2));
        }
    }


    public static void main(String[] args) {
    }
}
 
内容已经全部讲完，接下来请看全部完整代码： 
package lyq220104图形重绘;

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

public class DrawUI extends Jframe {

    String[] strs = {"直线", "圆", "矩形", "实心圆", "实心矩形"};
    Color[] color = {Color.WHITE,Color.BLACK,Color.yellow,Color.magenta,Color.DARK_GRAY};
    DrawListener dr = new DrawListener();//放到最前面，这样就可以让showDrawUI和Paint函数都能用到他们
    public void showDrawUI(){
        Jframe jf = this ;
        this.setTitle("图形重绘");
        this.setSize(800,800);
        jf.setDefaultCloseOperation(Jframe.EXIT_ON_CLOSE);
        jf.setVisible(true);

        FlowLayout fl = new FlowLayout();
        jf.setLayout(fl);

        for(int i=0;i 
package lyq220104图形重绘;

import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;

public class DrawListener implements MouseListener, ActionListener {
    int x1,x2,y1,y2;
    Graphics g;
    Color color = Color.black;
    String typeStr ="直线";

    @Override
    public void actionPerformed(ActionEvent e) {
        System.out.println("按钮被点击");
        String str = e.getActionCommand(); //例如 JButton aButton = new JButton("Today");
                                            // getActionCommand（）可以获取到Today
                                            // getSource()获取到的是aButton

        if (str.equals("")){
            System.out.println("这是一个颜色按钮");
            //获取点击的对象 按钮
            JButton jb = (JButton) e.getSource();
            //获取按钮背景颜色
            color = jb.getBackground();
            //设置给画笔对象
            g.setColor(color);
        }else{
            //如果不是空格 那就把字符存入typeStr
            typeStr = str;
        }
    }
    @Override
    public void mouseClicked(MouseEvent e) {

    }

    @Override
    public void mousePressed(MouseEvent e) {
        x1 = e.getX();
        y1 = e.getY();
    }

    Shape[] shapeList = new Shape[100];
    int shapeindex = 0;
    @Override
    public void mouseReleased(MouseEvent e) {
        x2 = e.getX();
        y2 = e.getY();
        Shape shape = new Shape ();
        shape.setshapeData(typeStr,x1,x2,y1,y2,color);
        // 绘制图形 调用的是图形的绘制方法
        shape.drawshape(g);
        // 将每次绘制的图形对象保存至数组中
        shapeList[shapeindex++] = shape;
        System.out.println("已经保存了"+shapeindex+"个图形");
    }

    @Override
    public void mouseEntered(MouseEvent e) {

    }

    @Override
    public void mouseExited(MouseEvent e) {

    }

}
 
package lyq220104图形重绘;

import java.awt.*;

public class Shape {
    String typename;
    int x1,x2,y1,y2;
    Color color;

    //设置图形数据
    public void setshapeData(String typename, int x1, int x2, int y1, int y2, Color color) {
        this.typename = typename;
        this.x1 = x1;
        this.x2 = x2;
        this.y1 = y1;
        this.y2 = y2;
        this.color = color;
    }

    public void drawshape(Graphics g){
        if(typename.equals("直线")){
            g.drawLine(x1,y1,x2,y2);
        }else if(typename.equals("矩形")){
            g.drawRect(Math.min(x1,x2),Math.min(y1,y2),Math.abs(x1-x2),Math.abs(y1-y2));
        }else if(typename.equals("圆")){
            g.drawOval(Math.min(x1,x2),Math.min(y1,y2),Math.abs(x1-x2),Math.abs(y1-y2));
        }else if(typename.equals("实心圆")){
            g.fillOval(Math.min(x1,x2),Math.min(y1,y2),Math.abs(x1-x2),Math.abs(y1-y2));
        }else if(typename.equals("实心矩形")){
            g.fillRect(Math.min(x1,x2),Math.min(y1,y2),Math.abs(x1-x2),Math.abs(y1-y2));
        }
    }


    public static void main(String[] args) {
    }
}

java图形重绘

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