一个很实用的JAVA教程

				// Cylinder.java
				// 定义Cylinder类
				
				public class Cylinder extends Circle {//圆柱继承圆
				   protected double height;  // 圆柱的高度
				   
				   // 构造函数
				   public Cylinder()      
				   {
				      // 隐含的调用父类的构造函数
				      setHeight( 0 );
				   }
				
				   // 构造函数
				   public Cylinder( double h, double r, int a, int b )      
				   {
				      super( r, a, b );   // 调用父类的构造函数
				      setHeight( h );
				   }
				
				   // 设置圆柱的高度
				   public void setHeight( double h )
				      { height = ( h >= 0 ? h : 0 ); }
				   
				   // 获得圆柱的高度
				   public double getHeight() { return height; }
				
				   // 计算圆柱的底面积 (i.e., surface area)
				   public double area()
				   {
				      return 2 * super.area() +
				             2 * Math.PI * radius * height;
				   }
				   
				   // 计算圆柱的体积
				   public double volume() { return super.area() * height; }
				
				   // 体积转换成字符串输出
				   public String toString()
				      { return super.toString() + "; Height = " + height; }
				
				   // 返回类的名字
				   public String getName() { return "Cylinder"; }
				}
				
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				 * (C) Copyright 1999 by Deitel & Associates, Inc. and Prentice Hall.     *
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