package ch07.ex07;

public class Parents {
	protected int x;
	protected int y;
	
	public Parents() {
		this.x=0;
		this.y=0;
	}
	
	public Parents(int x, int y) {
		this.x=x;
		this.y=y;
	}
	
	public void yunsan() {
		System.out.println("hap : " + (x + y));
	}
}

package ch07.ex07;

public class Son extends Parents{
	public Son() {
		super();
	}
	
	public Son(int x, int y) {
		super(x, y);
	}

	@Override
	public void yunsan() {
		System.out.println("cha : " + (x - y));
	}
	
	public void disp() {
		System.out.println("disp Function");
	}
}

package ch07.ex07;

public class Ex {
	public static void main(String[] args) {
		Son son=new Son(10, 20);
		son.yunsan();
		son.disp();
		
		Parents parent=new Parents(1, 3);
		parent.yunsan();
		
		Parents p=new Son(40, 20);	//UpCasting
		p.yunsan();
		p.disp()	//ERORR
	}

}

cha : -10
disp Function
hap : 4
cha : 20