Java 语法 索引 ----- 继承(Inheritance) 和重写(Overriding)

// Superclass (parent class)

class Fruit{

    public String flavor;

}



// Subclass (child class)

class Apple extends Fruit {

    public String variety;

}



//downcasting

Apple a = new Apple();

Fruit f = a;



Apple c = (f instanceof Apple) ? (Apple)f : null;

 

重写

class Rectangle{

    public int w = 10, h = 10;

    public int getArea() { return w * h; }

}



class Triangle extends Rectangle{

   //调用父构造函数

   public Triangle() { super(); }

   @Override

    public int getArea() { return w * h / 2; }

}



Rectangle o = new Triangle();

o.getArea(); // (50) calls Triangle's version

如果用关键字 final， 比如：  public final int getArea() { return w * h; } 这个方法不能被子类重写.

 

 

参考文献： Java Quick Syntax Reference by Mikael Olsson