在一个窗口上自动生成圆形、矩形、线条三种中的一种，并算出线条长度、圆形和矩形的周长和面积

思路：创建一个窗口类、形状类、矩形类、线条类、圆形类，在窗口中实现要求。

package mt.util;

import java.awt.Color;
/**
 * 工具
 * @author mt
 *
 */
public final class MyUtil {
	private MyUtil() {
		
	}
	/**
	 * 产生指定范围内的随机数
	 * @param min  最小值（闭区间）
	 * @param max  最大值（闭区间）
	 * @return 指定范围内的随机数
	 */
	public static int random(int min , int max) {
		return (int) (Math.random() * (max -min +1) +min);
	}
	
	public static Color randomColor() {
		int r = random(0,255);
		int g = random(0,255);;
		int b = random(0,255);;
		return new Color(r,g,b);
	}
	
}

package mt.shape;

import java.awt.Color;
import java.awt.Graphics;
/**
 * 图形（抽象的不能实例化）
 * @author mt
 *
 */
public abstract class Shape {
	protected int x1, y1;  //开始坐标
	protected int x2, y2;   //结束坐标
	protected Color color;
	/**
	 * 绘图（抽象方法留给子类重写）
	 * @param g 画笔
	 */
	public abstract void draw(Graphics g);

	public int getX1() {
		return x1;
	}

	public void setX1(int x1) {
		this.x1 = x1;
	}
	public int getY1() {
		return y1;
	}

	public void setY1(int y1) {
		this.y1 = y1;
	}

	public int getX2() {
		return x2;
	}

	public void setX2(int x2) {
		this.x2 = x2;
	}

	public int getY2() {
		return y2;
	}

	public void setY2(int y2) {
		this.y2 = y2;
	}

	public void setColor(Color color) {
		this.color = color;
	}


}

package mt.shape;

import java.awt.Graphics;
/**
 * 矩形
 * @author mt
 *
 */
public class Rectangle extends Shape {

	@Override
	public void draw(Graphics g) {
		int width = Math.abs(x1 - x2);
		int height = Math.abs(y1 - y2);		
		int x = x1 < x2? x1 : x2;
		int y = y1 < y2? y1 : y2;
		g.setColor(color);
		g.drawRect(x, y, width, height);
	}

}

package mt.shape;

import java.awt.Graphics;
/**
 * 圆形
 * @author mt
 *
 */
public class Oval extends Shape {

	@Override
	public void draw(Graphics g) {
		int width = Math.abs(x1 - x2);
		int height = Math.abs(y1 - y2);		
		int x = x1 < x2? x1 : x2;
		int y = y1 < y2? y1 : y2;
		g.setColor(color);
		g.drawOval(x, y, width, height);
	}

}

package mt.shape;

import java.awt.Graphics;
/**
 * 线条
 * @author mt
 *
 */
public class Line extends Shape {

	@Override
	public void draw(Graphics g) {
		g.setColor(color);
		g.drawLine(x1, y1, x2, y2);

	}

}

package mt.iu;

import java.awt.FlowLayout;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

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

import mt.shape.Line;
import mt.shape.Oval;
import mt.shape.Rectangle;
import mt.shape.Shape;
import mt.util.MyUtil;
/**
 * 我的窗口
 * @author mt
 *
 */
@SuppressWarnings("serial")
public class MyFrame extends JFrame {	
	/**
	 * 创建一个点击按钮后执行行为的类
	 * @author mt
	 *
	 */
	private class ButtonHander implements ActionListener{
		@Override
		public void actionPerformed(ActionEvent e) {
			String commond = e.getActionCommand();
			if (commond.equals("Line")) {
				shape = line;
			}
			else if (commond.equals("oval")) {
				shape = oval;
			}
			else {
				shape = rectangle;
			}
			shape.setX1(MyUtil.random(0, 800));
			shape.setY1(MyUtil.random(0, 700));
			shape.setX2(MyUtil.random(0, 800));
			shape.setY2(MyUtil.random(0, 700));
			shape.setColor(MyUtil.randomColor());

			repaint();
		}

	};

	private JButton lineButton ;  //画线按钮
	private JButton ovalButton ;  //画圆按钮
	private JButton rectangleButton ;  //画矩形按钮
	private Shape shape = null;  //图形
	private Line  line = new Line(); //线
	private Oval  oval = new Oval();  //圆形
	private Rectangle  rectangle = new Rectangle();  //矩形
	/**
	 * 设置窗口属性
	 */
	public MyFrame() {
		this.setTitle("*****绘图窗口*****");  //标题
		this.setSize(800,700);              //大小
		this.setResizable(false);          //是否能调整大小
		this.setLocationRelativeTo(null);  //居中
		this.setDefaultCloseOperation(EXIT_ON_CLOSE); //关闭窗口时结束程序
		lineButton = new JButton("Line"); //命名画线按钮为“Line”
		ovalButton = new JButton("oval"); //命名画圆按钮为“oval”
		rectangleButton = new JButton("rectangle");
		//*命名画矩按钮为“rectangle”
		ActionListener haander = new ButtonHander();
		lineButton.addActionListener(haander);
		ovalButton.addActionListener(haander);
		rectangleButton.addActionListener(haander);
		this.setLayout(new FlowLayout());
	/**
	 * 添加按钮
	 */
		this.add(lineButton);
		this.add(ovalButton);
		this.add(rectangleButton);


	}
	@Override
	public void paint(Graphics g) {	//在窗口用画笔绘制
		super.paint(g);	
		if (shape!= null) {
			shape.draw(g);
			double a = Math.abs(shape.getX1() - shape.getX2());//横坐标之差
			double b = Math.abs(shape.getY1() - shape.getY2());//纵坐标之差
			if (shape == line) {
				int L = (int) Math.sqrt(a * a + b * b);				
				g.drawString("线条长度："+ L, 100, 100);
			}
			if (shape == oval) {
				int c = (int) (( Math.PI * a<b?a:b) + 4 * Math.abs(a/2 - b/2) );				
				int s = (int) (Math.PI * a * b / 4);
				g.drawString("椭圆周长："+ c, 100, 100);
				g.drawString("椭圆面积："+ s, 100, 120);
			}
			if (shape == rectangle) {
				int s = (int) (a * b) ;		
				int c = (int) ((a + b) * 2);
				g.drawString("矩形面积："+ s, 100, 100);
				g.drawString("矩形周长："+ c, 100, 120);

			}
		}
	}

}

package mt.tese;

import mt.iu.MyFrame;

public class Test {
	public static void main(String[] args) {
		new MyFrame().setVisible(true);  //匿名对象
	}
}