Java的抽象方法和抽象类实例详解

public abstract class Shape
{
  {
   System.out.println("执行Shape的初始化块...");
  }
  private String color;
  // 定义一个计算周长的抽象方法
  public abstract double calPerimeter();
  // 定义一个返回形状的抽象方法
  public abstract String getType();
  // 定义Shape的构造器，该构造器并不是用于创建Shape对象，
  // 而是用于被子类调用
  public Shape(){}
  public Shape(String color)
  {
   System.out.println("执行Shape的构造器...");
   this.color = color;
  }
  // 省略color的setter和getter方法
  public void setColor(String color)
  {
   this.color = color;
  }
  public String getColor()
  {
   return this.color;
  }
}

public class Triangle extends Shape
{
  // 定义三角形的三边
  private double a;
  private double b;
  private double c;
  public Triangle(String color , double a
   , double b , double c)
  {
   super(color);
   this.setSides(a , b , c);
  }
  public void setSides(double a , double b , double c)
  {
   if (a >= b + c || b >= a + c || c >= a + b)
   {
     System.out.println("三角形两边之和必须大于第三边");
     return;
   }
   this.a = a;
   this.b = b;
   this.c = c;
  }
  // 重写Shape类的的计算周长的抽象方法
  public double calPerimeter()
  {
   return a + b + c;
  }
  // 重写Shape类的的返回形状的抽象方法
  public String getType()
  {
   return "三角形";
  }
}

public class Circle extends Shape
{
  private double radius;
  public Circle(String color , double radius)
  {
   super(color);
   this.radius = radius;
  }
  public void setRadius(double radius)
  {
   this.radius = radius;
  }
  // 重写Shape类的的计算周长的抽象方法
  public double calPerimeter()
  {
   return 2 * Math.PI * radius;
  }
  // 重写Shape类的的返回形状的抽象方法
  public String getType()
  {
   return getColor() + "圆形";
  }
  public static void main(String[] args)
  {
   Shape s1 = new Triangle("黑色" , 3 , 4, 5);
   Shape s2 = new Circle("黄色" , 3);
   System.out.println(s1.getType());
   System.out.println(s1.calPerimeter());
   System.out.println(s2.getType());
   System.out.println(s2.calPerimeter());
  }
}