클레스간 상속 (객체 생성 타입 케스팅 예제)

 

//CastChild.java

class CastChild extends CastParent {
 String name = "CastChild";
 int age = 20;

 CastChild(){
  System.out.println("CastChild타입의 객체 생성됨!");
 }
 CastChild(String name, int age) {
  System.out.println("CastChild타입 객체 생성됨!");
  this.name = name;
  this.age = age;
 }

 void method1(){
  System.out.println("CastChild의 method1()호출됨");
 }
 void method2(){
  System.out.println("CastChild의 method2()호출됨");
 }
 void method3(){
  System.out.println("CastChild의 method3()호출됨");
 }
}

----------------------------------------------------

//CastParent.java
class CastParent {
 String name = "CastParent";
 int age = 50;

 //생성자
 CastParent(){
  System.out.println("CastParent타입의 객체 생성됨!");
 }
 CastParent(String name, int age) {
  System.out.println("CastParent타입의 객체 생성됨!");
  this.name = name;
  this.age = age;
 }

 //메소드 오버라이드
 void method1() {
  System.out.println("CastParent의 method1() 호출됨");
 }

 void method2() {
  System.out.println("CastParent의 method2() 호출됨");
 }
}//class

----------------------------------------------------

//CastMain.java

class CastMain {
 public static void main(String[] args){
  CastParent cp1 = new CastParent(); //부모는 부모 자신을
  System.out.println(cp1.name+":"+cp1.age+"\n");

  CastChild cc1 = new CastChild(); //자식은 자식 자식을
  System.out.println(cc1.name+":"+cc1.age+"\n");

  CastParent cp2 = new CastChild(); //부모(상)는 자식(하)을 묵시적 변환
  System.out.println(cp2.name+":"+cp2.age+"\n");
  
  CastChild cc2 =(CastChild)cp2; //자식타입 cc2에 부모cp를 자식타입으로 변환 후
  System.out.println(cc2.name+":"+cc2.age+"\n");
  
  cp2.method1();
  cp2.method2();
//  cp2.method3();  //CastParent에는 Method3()없음
  
  System.out.println();
  cc2.method1();
  cc2.method2();
  cc2.method3();

  //부모의 method1()과 부모의 method2()호출
  System.out.println();
  CastParent cp3 = new CastParent();
  System.out.println(cp3.name+":"+cp3.age);

  cp3.method1();
  cp3.method2();

  // instanceof
  CastParent cp4 = new CastParent();
  CastChild cc4 = new CastChild();
  CastParent cp5 = cc4;
  if(cp4 instanceof CastParent) {
   System.out.println("41 cp4 is instance of CastParent");
  }
  if(cp4 instanceof CastChild) { //안찍힘.
   System.out.println("44 cp4 is instance of CastChild");
  }
  if(cc4 instanceof CastChild) {
   System.out.println("47 cc4 is instance of CastChild");
  }
  if(cc4 instanceof CastParent) {
   System.out.println("50 cc4 is instance of CastParent");
  }
  if(cp5 instanceof CastParent) {
   System.out.println("53 cp5 is instance of CastParent");
  }
  if(cp5 instanceof CastChild) {
   System.out.println("56 cp5 is instance of CastParent");
  }
  if(cc4 instanceof Object) {
   System.out.println("59 cc4 is instance of Object");
  }
 }
}//class