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Ch.09 인터페이스

인터페이스 선언

인터페이스의 구조 

[public] interface 인터페이스명 {
     [public abstract] 리턴타입 추상메서드명();
     [public] default 리턴타입 메서드명 (매개변수...) {...}
     [public] static 리턴타입 메서드명(매개변수...) {...}
}

:wr:상수 

package chapter09;

public interface InterfaceEx {

	// 상수
	public int MIN_PRICE = 0;
	public int MAX_PRICE = 100000;
	
	// 추상 메서드
	public double meanPrice();
	public double totalPrice();
	
	// default 메서드
	default double getSalePrice(double price) {
		return price - (price * 0.05);
	}
	
	// static 메서드
	static void printPrice(double price) {
		System.out.println(price);
	}
	
}

인터페이스 구현

Printer.java 

package chapter09;

public interface Printer {

	int INK = 100;
	void print();
	
}

Scanner.java 

package chapter09;

public interface Scanner {

	void scan();
	
}

Fax.java 

package chapter09;

public interface Fax {

	String FAX_NUMBER = "02-1234-5678";
	void send(String tel);
	void receive(String tel);
	
}

Complexer.java 

package chapter09;

public class Complexer implements Printer, Scanner, Fax {

	@Override
	public void send(String tel) {
		System.out.println(FAX_NUMBER + "에서 "+tel+"로 FAX 전송");
		
	}

	@Override
	public void receive(String tel) {
		System.out.println(tel + "에서 "+FAX_NUMBER+"로 FAX 수신");
		
	}

	@Override
	public void scan() {
		System.out.println("스캔 실행");
		
	}

	@Override
	public void print() {
		System.out.println("출력 실행");
		
	}

	
}

ComplexerMain.java 

package chapter09;

public class ComplexerMain {

	public static void main(String[] args) {
		
		Complexer com = new Complexer();
		System.out.println(Complexer.INK);
		System.out.println(Complexer.FAX_NUMBER);
		com.print();
		com.scan();
		com.send("02-8765-4321");
		com.receive("02-8765-4321");

	}

}

:wr:익명구현객체 

인터페이스 객체명 = new 인터페이스(){
// 인터페이스의 모든 추상 메서드 구현
};

package chapter09;

public class ComplexerMain2 {

	public static void main(String[] args) {
		
		Fax fax = new Fax() {

			@Override
			public void send(String tel) {
				System.out.println("여기는 익명 구현 객체의 send()");
				
			}

			@Override
			public void receive(String tel) {
				System.out.println("여기는 익명 구현 객체의 receive()");
				
			}
			
		};
		
		fax.send("1234");
		fax.receive("5678");
	}
}

ComplexcerInterFace.java 

package chapter09;

public interface ComplexcerInterface extends Printer, Scanner, Fax {

}

ComplexerMain3.java 

package chapter09;

public class ComplexerMain3 {

	public static void main(String[] args) {
		
		ComplexcerInterface ci = new ComplexcerInterface() {

			@Override
			public void send(String tel) {
				System.out.println("여기는 익명 구현 객체의 send()");
				
			}

			@Override
			public void receive(String tel) {
				System.out.println("여기는 익명 구현 객체의 receive()");
				
			}

			@Override
			public void print() {
				System.out.println("여기는 익명 구현 객체의 print()");
				
			}

			@Override
			public void scan() {
				System.out.println("여기는 익명 구현 객체의 scan()");
				
			}
			
		};
		
		ci.send("1234");
		ci.receive("5678");
		ci.print();
		ci.scan();
	}
}

인터페이스의 다형성

GraphiicCard.java 

package chapter09;

public interface GraphicCard {

	String MEMORY = "2G";
	
	public void process();
	
}

Amd.java 

package chapter09;

public class Amd implements GraphicCard {

	public void process() {
		System.out.println("AMD 그래픽 처리");
	}
	
}

Nvidia.java 

package chapter09;

public class Nvidia implements GraphicCard {

	public void process() {
		System.out.println("Nvidia 그래픽 처리");
	}
	
}

Computer.java 

package chapter09;

public class Computer {

	public static void main(String[] args) {
		
		GraphicCard gc = new Amd();
		
		System.out.println("메모리 : "+gc.MEMORY);
		
		// Amd로 생성
		gc = new Amd(); // 자동 형변환
		gc.process();
		
		// Nvidia로 교체
		gc = new Nvidia(); // 자동 형변환
		gc.process();
		
	}

}

:wr:매개 변수의 다형성 

package chapter08.poly;

public class Game {

	void display(GraphicCard gc) {
		gc.process();
	}
	
}


Game g = new Game();
Amd gc = new Amd();
g.display(gc);

Nvidia gc2 = new Nvidia();
g.display(gc2);

:wr:강제 형변환

Animal.java 

package chapter09;

public interface Animal {
	
	void sleep();
}

Eagle.java 

package chapter09;

public class Eagle implements Animal {

	public void sleep() {
		System.out.println("잠을 잔다.");
	}
	
	public void eat() {
		System.out.println("먹는다.");
	}

	
}

AnimalMain.java 

package chapter09;

public class AnimalMain {

	public static void main(String[] args) {
		
		Animal eagle = new Eagle();
		
		eagle.sleep();
		// eagle.eat(); // 에러
		
		Eagle eagleObj = (Eagle)eagle; // 강제 형변환
		eagleObj.eat(); // Eagle 클래스의 eat() 메서드
		
		System.out.println(eagle instanceof Animal);
	}
}

:wr:instanceof 

객체 isntanceof 클래스(인터페이스)

A.java 

package chapter09;

public interface A {

	void a();
}

AA.java 

package chapter09;

public interface AA extends A {

	void aa();
}

AAA.java 

package chapter09;

public class AAA implements AA {

	@Override
	public void a() {
		
	}
	
	@Override
	public void aa() {
		
	}

}

AB.java 

package chapter09;

public interface AB extends A {

	void ab();
}

ABB.java 

package chapter09;

public class ABB implements AB {

	@Override
	public void a() {
		
	}

	@Override
	public void ab() {
		
	}

}

InstanceofEx.java 

package chapter09;

public class InstanceofEx {

	public static void main(String[] args) {
		A a = new AAA();
		
		AA aa = new AAA();
		AAA aaa = new AAA();
		
		A b = new ABB();
		AB ab = new ABB();
		ABB abb = new ABB();
		
		System.out.println("a > A : " + (a instanceof A));
		System.out.println("aa > A : " + (aa instanceof A));
		System.out.println("aaa > A : " + (aaa instanceof A));
		
		System.out.println("aaa > AB : " + (aaa instanceof AB));

	}

}

default 메서드와 static 메서드

MyInterface1.java 

package chapter09;

public interface MyInterface1 {

	default void defaultMethod() {
		System.out.println("MyInterface1 의 default 메서드");
	}
	
	static void staticMethod() {
		System.out.println("MyInterface1의 static 메서드");
	}
}

MyInterface2.java 

package chapter09;

public interface MyInterface2 {

	default void defaultMethod() {
		System.out.println("MyInterface2 의 default 메서드");
	}
	
	static void staticMethod() {
		System.out.println("MyInterface2의 static 메서드");
	}
}

Parent.java 

package chapter09;

public class Parent {

	public void method2() {
		System.out.println("Parent 클래스의 method2()");
	}
}

Child.java 

package chapter09;

public class Child extends Parent implements MyInterface1, MyInterface2 {

	@Override
	public void defaultMethod() {
		System.out.println("Child 클래스의 default 메서드");
		MyInterface1.super.defaultMethod();
		MyInterface2.super.defaultMethod();
	}
	
	

}

DefaultStaticEx.java 

package chapter09;

public class DefaultStaticEx {

	public static void main(String[] args) {
		
		Child c = new Child();
		c.defaultMethod();
		c.method2();
		
		MyInterface1.staticMethod();
		MyInterface2.staticMethod();

	}

}

어노테이션

UserAnnot.java 

package chapter09;

import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;

@Retention(RetentionPolicy.RUNTIME)
public @interface UserAnnot {

	String value();
	int number() default 5;
	
}

UserClass.java 

package chapter09;

public class UserClass {

	@UserAnnot(value="A")
	public void methodA() {
		System.out.println("methodA() 실행");
	}
	
	@UserAnnot(value="B", number=10)
	public void methodB() {
		System.out.println("methodB() 실행");
	}
}

AnnotationEx.java 

package chapter09;

import java.lang.reflect.Method;

public class AnnotationEx {

	public static void main(String[] args) throws Exception {
		
		Method method[] = UserClass.class.getDeclaredMethods();
		
		for (int i=0; i<method.length; i++) {
			String methodName = method[i].getName();
			UserAnnot annot = method[i].getAnnotation(UserAnnot.class);
			
			System.out.print(methodName + "의 어노테이션 ");
			System.out.print("value : "+annot.value() + " ");
			System.out.print("number : "+annot.number() + " ");
			System.out.println();
			
			method[i].invoke(new UserClass(), null); // 메서드 실행
		}

	}

}

마지막으로 수정됨: 2023/07/13 17:29
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