상속

이렇게 종속관계가 명확할 때 상속을 사용해야 한다.

package ex03.inheritance.extends00;

//상속
//1. 클래스를 잘 설계해 놓는다
//2. 상속만 받아도 그대로 물려받는다
//3. 물려받은 모든 기능을 사용할 수 있다


public class ExtendsMain {
	public static void main(String[] args) {
		GrandFather gFather = new GrandFather();
		gFather.handsome();
		
		Father father = new Father();
		father.handsome();
		father.wealth();
		
		Child child = new Child();
		child.handsome();
		child.wealth();
		child.play();
	}
}

---

package ex03.inheritance.extends00;

//java의 모든 클래스는 컴파일 되는 순간
//자동으로 java.lang.object 클래스의 상속을 받는다.

public class GrandFather {
	
	public void handsome() {
		System.out.println("잘 생겼다~");
	}
	
}

---

package ex03.inheritance.extends00;

public class Father extends GrandFather{
	public void wealth() {
		System.out.println("부유하다~");
	}
}

---

package ex03.inheritance.extends00;

public class Child extends Father{
	public void play() {
		System.out.println("인생을 즐긴다~");
	}
}

---

package ex03.inheritance.extends02;
/*
자식객체가 생성될 때
내부적으로 부모 객체가 먼저 생성된다
부모 객체가 자식 내부에 생성되기 때문에
자식은 부모의 기능을 사용할 수 있게 된다
*/
public class ExtendsMain {
	public static void main(String[] args) {
		
//		Child child = new Child();
		Child child = new Child(50,10000000L,20);
		
		child.play();		// Child
		child.wealth();		// Father
		child.handsome();	// GrandFather
	}
}

package ex03.inheritance.extends02;

//java의 모든 클래스는 컴파일되는 순간
//자동으로 java.lang.object 클래스의 상속을 받는다

public class GrandFather {
	
	int handsomeScore=100;
	
	public GrandFather() {
		System.out.println("GrandFather 생성자");
	}
	
	public GrandFather(int handsome) {
		this.handsomeScore = handsome;
		System.out.println("GrandFather 매개변수 생성자");
	}

	public void handsome() {
		System.out.println("점수: " + handsomeScore + " 잘 생겼다~");
	}
}

package ex03.inheritance.extends02;

public class Father extends GrandFather {
	
	long money = 9999999999999L;
	
	public Father() {
		System.out.println("Father 생성자");
	}
	public Father(long money) {
		this.money = money;
		System.out.println("Father 매개변수 1개 생성자");
	}
	public Father(int handsome, long money) {
		super(handsome);		//GrandFather 생성
		this.money = money;
		System.out.println("Father 매개변수 2개 생성자");
	}
	
	
	public void wealth() {
		System.out.println("재산 : " + money + "부유하다~");
	}
}

package ex03.inheritance.extends02;

public class Child extends Father{
	int duration=365;
	
	public Child() {
		System.out.println("Child 생성자");
	}
	public Child(int duration) {
		this.duration = duration;
		System.out.println("Child 매개변수 1개 생성자");
	}
	public Child(int handsome, long money, int duration) {
		super(handsome, money);	   //Father 생성자 
		this.duration = duration;
		System.out.println("Child 매개변수 3개 생성자");
	}
	
	public void play() {
		System.out.println(duration + "일 동안 인생을 즐긴다~");
	}
}

---

메서드 기능

package ex03.inheritance.extends03;

public class ExtendsMain {

	public static void main(String[] args) {
		Child child = new Child();
		
		
		child.play();
		child.wealth();
		child.handsome();
	}

}

package ex03.inheritance.extends03;

public class Grandfather {

	public Grandfather() {
		System.out.println("Grandfather 생성자");
	}
	
	public void handsome() {
		System.out.println("잘생겼다~ ");
	}
}

package ex03.inheritance.extends03;

public class Father extends Grandfather{
	
	public Father() {
		System.out.println("Father 생성자 ");
	}

	public void wealth() {
		System.out.println("부유하다~ ");
	}
}

package ex03.inheritance.extends03;

public class Child extends Father{
	public Child() {
		System.out.println("Child 생성자 ");
	}
	
	//물려 받은 메서드를 덮어쓴다 
	public void handsome() {
		System.out.println("뺀질거리게 생겼다~");
	}
	
	// 물려받은 메서드의 기능을 확장했다  
	public void wealth() {
		super.wealth();	//Father의 wealth
		System.out.println("돈을 많이 썼다! ");
		
	}
	
	//물려받지 않은 새롭게 정의한 메서드 
	public void play() {
		System.out.println("인생을 즐긴다~ ");
	}
}