java实验报告_继承多态（浙江大学慕课瓮恺）

Java程序设计实验报告

 

 

第六次实验设计

 

一、实验内容

题目：基于类继承和多态，在我们上午课程Shapes程序的基础上编写一个画图程序，在已有Shape、Line、Circle、Rectangle、Triangle的基础上增加Square和Ellipse两种新的类，并支持图形面积和周长的计算（Line面积设置为0）。

提示：

• 考虑下图中类的继承关系是否合理？如果不合理应该如何改进？

答：正方形是一种矩形，但 是不应该定义一个 Square 类来扩展 Rectangle 类，因为 width 和 height 属性并不适 合于正方形。应该定义一个继承自 Shape 类的 Square 类，并为正方形的 边定义一个 side 属性。

• 为类Sharp增加抽象函数getArea(), getPerimeter()，在子类中实现它们。

 

• 从数学上，正方形是一种特殊的矩形。但是，从程序实现上考虑，正方形只要一个边长，而矩形可以从正方形继承后再增加一个边长成员变量。另一方面来说，如果正方形从矩形继承，那么就会出现冗余的第二个边长变量

 

二、实验运行结果

注意：将程序运行结果截图粘贴在此处

 

三、程序源代码

注意：将程序代码粘贴在此处，注意源代码中注释行数不少于全部代码的1/5

1. MyPic类：

package shapes;
public class MyPic {
	public static void main(String[] args) 
	{
		Picture pic = new Picture(420,300);

		//新建图形
		Ellipse e1 = new Ellipse(50,50,50,60);//新增的椭圆
		Circle c1 = new Circle(320,40,80);
		Square square = new Square(350,150,50);//新增的正方形
		Rectangle r1 = new Rectangle(100, 100, 100, 100);
		Triangle t1 = new Triangle(100, 100, 200, 100, 150, 50);
		Line l1 = new Line(0,205,400,205);


		pic.add(c1);
		pic.add(r1);
		pic.add(t1);
		pic.add(l1);

		//把新增的加入进去
		pic.add(square);
		pic.add(e1);


		//画图
		pic.draw();

		//对面积计算的测试
		System.out.println("椭圆e1的面积："+e1.getArea()+"，周长"+e1.getPerimeter());
		System.out.println("圆c1的面积："+c1.getArea()+"，周长"+c1.getPerimeter());
		System.out.println("正方形square的面积："+square.getArea()+"，周长"+square.getPerimeter());
		System.out.println("长方形r1的面积："+square.getArea()+"，周长"+square.getPerimeter());
		System.out.println("线l1的面积："+l1.getArea()+"，周长"+l1.getPerimeter());
		System.out.println("三角形t1的面积："+t1.getArea()+"，周长"+t1.getPerimeter());



	}
}

2. Picture类 

package shapes;

import java.awt.Graphics;
import java.util.ArrayList;

import javax.swing.JFrame;
import javax.swing.JPanel;

public class Picture extends JFrame {
	private static final long serialVersionUID = 1L;
	private int width;
	private int height;
	
	private ArrayList listShape = new ArrayList();
	
	private class ShapesPanel extends JPanel {
		private static final long serialVersionUID = 1L;

		@Override
		protected void paintComponent(Graphics g) {
			super.paintComponent(g);
			for ( Shape s : listShape )
			{
				s.draw(g);
			}			
		}
		
	}
	
	public void add(Shape s)
	{
		listShape.add(s);
	}

	public Picture(int width, int height)
	{
		add(new ShapesPanel());
		this.setDefaultCloseOperation(EXIT_ON_CLOSE);
		this.width = width;
		this.height = height;
	}
	
	public void draw()
	{
		setLocationRelativeTo(null);
		setSize(width, height);
		setVisible(true);
	}
}

3. Shape类

package shapes;

import java.awt.Graphics;

public abstract class Shape {
	
	public abstract void draw(Graphics g);

	//计算周长和面积的抽象函数
	public abstract double getPerimeter();
	public abstract double getArea();

	public static void main(String[] args) {

	}
	
}

4. Line类

 

package shapes;

import java.awt.Graphics;

public class Line extends Shape {

	private int x1;
	private int y1;
	private int x2;
	private int y2;
	
	public Line(int x1, int y1, int x2, int y2)
	{
		this.x1 = x1; this.y1 = y1;
		this.x2 = x2; this.y2 = y2;
	}

	//抽象函数的重载
	@Override
	public void draw(Graphics g) {
		g.drawLine(x1, y1, x2, y2);
	}


	@Override
	public double getPerimeter() {
		return Math.sqrt((y1-y2)*(y1-y2) + (x1-x2)*(x1-x2));
	}

	@Override
	public double getArea() {
		return 0;
	}


}

5. Square类

package shapes;

import java.awt.*;

public class Square extends Shape {

    public int x,y;
    public int side;

    //构造函数
    public Square() {
    }

    public Square(int x, int y, int side) {
        this.x = x;
        this.y = y;
        this.side = side;
    }

    @Override
    public void draw(Graphics g) {
        g.drawRect(x,y,side,side);
    }

    @Override
    public double getPerimeter() {
        return 4 * side;
    }

    @Override
    public double getArea() {
        return side *side;
    }
}

6. Rectangle类

package shapes;

import java.awt.Graphics;

public class Rectangle extends Shape {
	private int x;
	private int y;
	private int width;
	private int height;
	
	public Rectangle(int x, int y, int width, int height) {
		this.x = x;
		this.y = y;
		this.width = width;
		this.height = height;
	}

	@Override
	public void draw(Graphics g) {
		g.drawRect(x, y, width, height);
	}

	//重写抽象方法
	@Override
	public double getPerimeter() {
		return 2 * (width + height);
	}

	@Override
	public double getArea() {
		return width * height;
	}

}

7. Ellipse类

package shapes;

import java.awt.*;

public class Ellipse extends Shape{


    public int x;
    public int y;
    public int a;
    public int b;

    public Ellipse(int x, int y, int a, int b) {
        this.x = x;
        this.y = y;
        this.a = a;
        this.b = b;
    }
    @Override
    public void draw(Graphics g) {
           g.drawOval(x,y,a,b);
    }

    @Override
    public double getPerimeter() {

        return 2 * Math.PI + 4 * (a - b);
    }

    @Override
    public double getArea() {
        return Math.PI * a * b;
    }
}

8. Circle类

package shapes;

import java.awt.Graphics;

public class Circle extends Ellipse {

	
	public Circle(int x, int y, int radius)
	{
		super(x,y,radius,radius);
	}

}

9.Triangle类

package shapes;

import java.awt.Graphics;

public class Triangle extends Shape {
	private int[] x = new int[3];
	private int[] y = new int[3];
	
	public Triangle(int x1, int y1, int x2, int y2, int x3, int y3)
	{
		x[0] = x1; x[1] = x2; x[2] = x3;
		y[0] = y1; y[1] = y2; y[2] = y3;
	}
	
	@Override
	public void draw(Graphics g) {
		g.drawPolygon(x, y, x.length);
	}

	@Override
	public double getPerimeter() {
		double s1 = Math.sqrt(Math.pow(x[1] - x[2], 2) + Math.pow(y[1] - y[2], 2));
		double s2 = Math.sqrt(Math.pow(x[1] - x[0], 2) + Math.pow(y[1 ]- y[0], 2));
		double s3 = Math.sqrt(Math.pow(x[0] - x[2], 2) + Math.pow(y[0] - y[2], 2));
		return s1+s2+s3;
	}

	//利用海伦公式计算面积
	@Override
	public double getArea() {
		double s1 = Math.sqrt(Math.pow(x[1] - x[2], 2) + Math.pow(y[1] - y[2], 2));
		double s2 = Math.sqrt(Math.pow(x[1] - x[0], 2) + Math.pow(y[1 ]- y[0], 2));
		double s3 = Math.sqrt(Math.pow(x[0] - x[2], 2) + Math.pow(y[0] - y[2], 2));
		double s = (s1 + s2 + s3) / 2;

		return  Math.sqrt(s * (s - s1) * (s - s2) * (s - s3));
	}

}