实验五 继承与多态

实验五继承与多态

专业班级学号姓名

实验学时 2 实验类型验证性实验地点数计学院实验中心实验时间指导老师

实验成绩

年月日一、实验目的：

理解继承与多态的概念，掌握三种访问控制的区别，掌握抽象类、接口与包的应用。

二、实验内容：

1. 参考教材P124，示例程序C5_17，掌握抽象类的应用。

2. 参考教材P128，示例程序C5_18，掌握接口的使用方法。

3. 参考教材P133，示例程序C5_20，掌握包的使用方法。

三、实验要求：

1.完成示例程序的验证。

2.写出实验报告。

四、实验步骤与结果：（由学生按照实验内容完成）

程序一

package ch01;

import java.applet.Applet;

import java.awt.Graphics;

abstract class Shapes //定义一个抽象类Shapes

{

public int x,y; //x、y为画图的坐标

public int width,height;

public Shapes(int x,int y,int width,int height)

{ this.x=x;

this.y=y;

this.width=width;

this.height=height;

}

abstract double getArea( ); //求图形面积的抽象方法

abstract double getPerimeter( ); //求图形周长的抽象方法

}

class Square extends Shapes //由抽象类Shapes派生的子类——矩形类

{

@Override

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

@Override

public double getPerimeter( ){return(2*width+2*height);}

public Square(int x,int y,int width,int height)

{ super(x,y,width,height); }

}

class Triangle extends Shapes //由抽象类Shapes派生的子类——三角形类{

public double c; //斜边

@Override

public double getArea( ){return(0.5*width*height);}

@Override

public double getPerimeter( ){return(width+height+c);}

public Triangle(int x,int y,int base,int height)

{

super(x,y,base,height);

c=Math.sqrt(width*width+height*height);

}

}

class Circle extends Shapes //由抽象类Shapes派生的子类——圆类

{

public double r; //半径

@Override

public double getArea( ){return(r*r*Math.PI);}

@Override

public double getPerimeter( ){return(2*Math.PI*r);}

public Circle(int x,int y,int width,int height)

{

super(x,y,width,height);

r=(double)width/2.0;

}

}

public class Ch01 extends Applet

{

Square Box=new Square(5,15,25,25);

Triangle tri=new Triangle(5,50,8,4);

Circle Oval=new Circle(5,90,25,25);

@Override

public void paint(Graphics g)

{

//画正方形

g.drawRect(Box.x,Box.y,Box.width,Box.height);

g.drawString("Box Area:"+Box.getArea( ),50,35);

g.drawString("Box Perimeter:"+Box.getPerimeter( ),50,55);

g.drawString("tri Area:"+tri.getArea( ),50,75);

g.drawString("tri Perimeter:"+tri.getPerimeter( ),50,95);

g.drawOval(Oval.x,Oval.y,Oval.width,Oval.height); //画圆

g.drawString("oval Area:"+Oval.getArea( ),50,115);

}

}

程序二

package ch02;

import java.applet.Applet;

import java.awt.Graphics;

interface Shapes //定义一个接口

{

abstract double getArea( ); //自动被定义为public

double getPerimeter( );

}

class Square implements Shapes //类要实现接口

{

public int x,y;

public int width,height;

@Override

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

@Override

public double getPerimeter( ){return(2*width+2*height);} public Square(int x,int y,int width,int height)

{

this.x=x;

this.y=y;

this.width=width;

this.height=height;

}

}

class Triangle implements Shapes //类要实现接口

{

public int x,y;

public int width,height;

public double c;

@Override

public double getArea( ){return(0.5*width*height);}

@Override

public double getPerimeter( ){return(width+height+c);} public Triangle(int x,int y,int base,int height)

{

this.x=x;

this.y=y;

width=base;

this.height=height;

c=Math.sqrt(width*width+height*height);

}

}