다형성

Java 프로그래밍 - 다형성

class Person {
    public void print() {
        System.out.println("Person.print");
    }
}

class Student extends Person {
    public void print() {
        System.out.println("Student.print");
    }

    public void print2() {
        System.out.println("Student.print2");
    }
}

class CollegeStudent extends Person {
    public void print() {
        System.out.println("CollegeStudent.print");
    }
}


public class Main {

    public static void main(String[] args) {

//      1. 다형성
        System.out.println("== 다형성 ==");
        Person p1 = new Person();
        Student s1 = new Student();

        Person p2 = new Student();
//        Student s2 = new Person();

        p1.print();
        s1.print();
        s1.print2();
        p2.print();
//        p2.print2();

        Person p3 = new CollegeStudent();
//        CollegeStudent c1 = new Student();
        p3.print();


//      2. 타입 변환
        System.out.println("== 타입 변환 ==");
        Person pp1 = null;
        Student ss1 = null;

        Person pp2 = new Person();
        Student ss2 = new Student();
        Person pp3 = new Student();     // 업캐스팅

        pp1 = pp2;
        pp1 = ss2;

        ss1 = ss2;
//        ss1 = (Student)pp2;
        ss1 = (Student)pp3; // 다운캐스팅

//        CollegeStudent cc1;
//        CollegeStudent cc2 = new CollegeStudent();
//        ss1 = (Student) cc2;
//        cc1 = (CollegeStudent) ss2;


//      3. instanceof
        System.out.println("== instanceof ==");
        Person pe1 = new Person();
        Student st1 = new Student();
        Person pe2 = new Student();
        Person pe3 = new CollegeStudent();

        System.out.println("== instance of ==");
        System.out.println(pe1 instanceof Person);
        System.out.println(pe1 instanceof Student);

        System.out.println(st1 instanceof Student);
        System.out.println(st1 instanceof Person);

        System.out.println(pe2 instanceof Person);
        System.out.println(pe2 instanceof Student);

        System.out.println(pe3 instanceof Person);
        System.out.println(pe3 instanceof CollegeStudent);

        if (pe1 instanceof Student) {
            Student stu1 = (Student) pe1;
        }

        if (st1 instanceof Person) {
            Person per1 = (Person)st1;
        }

    }
}

== 다형성 ==
Person.print
Student.print
Student.print2
Student.print
CollegeStudent.print
== 타입 변환 ==
== instanceof ==
== instance of ==
true
false
true
true
true
true
true
true

// Practice
// 아래의 클래스와 상속 관계에서 다형성을 이용하여
// Car 객체를 통해 아래와 같이 출력될 수 있도록 Test code 부분을 구현해보세요.
// 빵빵!
// 위이잉!
// 삐뽀삐뽀!

class Car {
    Car(){}
    public void horn() {
        System.out.println("빵빵!");
    }
}

class FireTruck extends Car {
    public void horn() {
        System.out.println("위이잉!");
    }
}

class Ambulance extends Car {
    public void horn() {
        System.out.println("삐뽀삐뽀!");
    }
}

public class Practice {
    public static void main(String[] args) {
        // Test code
        Car car = new Car();
        car.horn();

        car = new FireTruck();
        car.horn();

        car = new Ambulance();
        car.horn();

        Car car2[] = {new Car(), new FireTruck(), new Ambulance()};

        for (Car item: car2) {
            item.horn();
        }
    }
}

빵빵!
위이잉!
삐뽀삐뽀!
빵빵!
위이잉!
삐뽀삐뽀!