简单的类的继承的示例

package point;

public class MyPoint {
    
        protected int x;
        protected int y;
        
        public MyPoint(){
            
        }
        public MyPoint (int x,int y){
            this.x=x;
            this.y=y;
        }
        public void setX(int x) {
                    this.x = x;
                }
        public int getX() {
            return x;
        }

        public void setY(int y) {
            this.y = y;
        }

        public int getY() {
            return y;
        }

        
        public String toString (){
            return"("+x+","+y+")";
        
        }
        
    }

package point;

public class MyCircle extends MyPoint {
    protected int radius;
    
    public MyCircle(){
        System.out.println("调用mycircle类的无参数构造方法");
        
    }
    public MyCircle(int x,int y,int radius){
        this.x=x;
        this.y=y;
        this.radius=radius;
        
    }
    public void setRadius(int radius){
        if(radius>0)
            this.radius=radius;
    }
    public int getRadius(){
        return radius;    
    }
    public double area (){
        return Math.PI*radius*radius;
    }
    public String toString(){
        return "圆心:"+super.toString()+";半径："+radius;
    }
}

package point;

import point.MyCircle;
public class TestMyCircle {
    public static void main(String args[]){
        MyCircle obj=new MyCircle(10,10,5);
        System.out.println(obj.toString());
        System.out.println("圆的面积："+obj.area());
        
        obj.setX(5);
        obj.setY(10);
        obj.setRadius(10);
        System.out.println(obj.toString());
        System.out.println("圆的面积："+obj.area());
    }
}

mypoint为父类，mycircle为其子类，子类继承父类之后，对于某些方法需要重写覆盖才能正常使用。

如果要在子类中调用被隐藏的变量，被覆盖的方法只需super一下就行了

super.变量名；

super.方法名；

super(参数)；