java 派生类 与 this,super

class Point{
   protected int x, y;    // coordinates of the Point
   public Point(){        //不带参数的构造方法
      x=0;
      y=0;
      System.out.println( "Point constructor: "+this.toString() );
   }
   public Point(int a,int b){   //带参数的构造方法
      x=a;
      y=b;
      System.out.println( "Point constructor: "+this.toString() );//this 是指向子类的对象指针
   }
   public String toString() 
      { return "["+x+","+y+"]"; }
}
class Circle extends Point {     // Circle类继承Point类
       protected double radius;
       public Circle(){
         super(4,5);           //引用父类带参数的构造方法
         radius=10;        
         System.out.println( "Circle constructor: "+this.toString() );
       }
        public String toString(){
          return "Center = "+super.toString()+"Radius="+radius;//super 指向父类的对象指针
       }
    }
    public class first {
       public static void main( String args[] ){
      Circle circle1=new Circle();  /*建Circle对象，首先执行父类Point类的无参数构造方法，然后执行子类Circle类的构造方法*/
       }
    }

在main()是开始构造Circle()类，接着又super(4,5);           //引用父类带参数的构造方法

构造Point(4,5)

其中this 是指向子类的对象指针

super 指向父类的对象指针