java 버전 별 인터페이스 메소드

출처

howtodoinjava.com/java9/java9-private-interface-methods/

 

요약

자바 버전별 인터페이스에 선언 및 구현 할 수 있는 메소드

java7, java8 이라는 명칭은 안 맞는다. (그 당시는 1.7,1.8 이었으니)

 

개인의견이지만 interface 와 abstract class 간 구분이 없어지는 것 같아서 조금 그렇다.

public abstract	N/A
public default	java8 이상
public static	java8 이상
private	java9 이상
private static	java9 이상

java 7 이전

package before_java7;

public interface SomeInterface {
    //public abstract 는 생략 가능
    public abstract void someMethod();
}

package before_java7;

public class BeforeJava7 implements SomeInterface {

    @Override
    public void someMethod() {
        System.out.println("override some method(public abstract)");
    }

    public static void main(String args[]) {
        SomeInterface instance = new BeforeJava7();
        instance.someMethod();
    }
}

override some method(public abstract)

java 8

package java8;

public interface SomeInterface {
    //public abstract 는 생략 가능
    public abstract void someMethod();

    public default void someMethod2() {
        System.out.println("public default method");
    }

    public static void someMethod3() {
        System.out.println("public static method");
    }
}

package java8;

public class Java8 implements SomeInterface {
    @Override
    public void someMethod() {
        System.out.println("override some method(public abstract)");
    }

    public static void main(String args[]) {
        SomeInterface instance = new Java8();
        instance.someMethod();
        instance.someMethod2();
        SomeInterface.someMethod3();
    }
}

override some method(public abstract)
public default method
public static method

java 9

package after_java9;

public interface SomeInterface {
    //public abstract 는 생략 가능
    public abstract void someMethod();

    public default void someMethod2() {
        System.out.println("call private (default) method");
        someMethod4();
        System.out.println("call private static method");
        someMethod5();
        System.out.println("public default method");
    }

    public static void someMethod3() {
        System.out.println("public static method");
    }

    //default 인 것 같은데 선언은 안된다.
    private void someMethod4(){
        System.out.println("private method");
    }

    private static void someMethod5() {
        System.out.println("private static method");
    }
}

package after_java9;


public class Java9 implements SomeInterface {
    @Override
    public void someMethod() {
        System.out.println("override some method(public abstract)");
    }

    public static void main(String args[]) {
        SomeInterface instance = new Java9();
        instance.someMethod();
        instance.someMethod2();
        SomeInterface.someMethod3();
    }
}

override some method(public abstract)
call private (default) method
private method
call private static method
private static method
public default method
public static method

기타

java 는 다중상속을 제한하는게 기본 방침일텐데 이런 식이면 의미가 없어지지 않나 해서 추가 테스트

컴파일 타임에서 강제한다.

메소드 이름이 같으니 (시그네쳐도 같긴한데) override 하라고 강제

 

package after_java9;

public interface SomeInterface1 {
    //public abstract 는 생략 가능
    public abstract void someMethod();

    public default void someMethod2() {
        System.out.println("SomeInterface1: call private (default) method");
        someMethod4();
        System.out.println("SomeInterface1: call private static method");
        someMethod5();
        System.out.println("SomeInterface1: public default method");
    }

    public static void someMethod3() {
        System.out.println("SomeInterface1: public static method");
    }

    //default 인 것 같은데 선언은 안된다.
    private void someMethod4(){
        System.out.println("SomeInterface1: private method");
    }

    private static void someMethod5() {
        System.out.println("SomeInterface1: private static method");
    }
}

package after_java9;

public interface SomeInterface2 {
    //public abstract 는 생략 가능
    public abstract void someMethod();

    public default void someMethod2() {
        System.out.println("SomeInterface2: call private (default) method");
        someMethod4();
        System.out.println("SomeInterface2: call private static method");
        someMethod5();
        System.out.println("SomeInterface2: public default method");
    }

    public static void someMethod3() {
        System.out.println("SomeInterface2: public static method");
    }

    //default 인 것 같은데 선언은 안된다.
    private void someMethod4(){
        System.out.println("SomeInterface2: private method");
    }

    private static void someMethod5() {
        System.out.println("SomeInterface2: private static method");
    }
}

package after_java9;


public class Java9 implements SomeInterface1, SomeInterface2 {
    @Override
    public void someMethod() {
        System.out.println("override some method(public abstract)");
    }

    // default method 이름이 충돌나니 override 를 필수로 하게 하며 안하면 에러를 뱉는다
    //java: types after_java9.SomeInterface1 and after_java9.SomeInterface2 are incompatible;
    //  class after_java9.Java9 inherits unrelated defaults for someMethod2() from types after_java9.SomeInterface1 and after_java9.SomeInterface2
    @Override
    public void someMethod2() {
        System.out.println("override some method2");
    }

    public static void main(String args[]) {
        System.out.println("=====INTERFACE1=====");
        SomeInterface1 instance1 = new Java9();
        instance1.someMethod();
        instance1.someMethod2();
        SomeInterface1.someMethod3();
        System.out.println("=====INTERFACE1=====");
        System.out.println();

        System.out.println("=====INTERFACE2=====");
        SomeInterface2 instance2 = new Java9();
        instance2.someMethod();
        instance2.someMethod2();
        SomeInterface2.someMethod3();
        System.out.println("=====INTERFACE2=====");
        System.out.println();

        System.out.println("=====CLASS=====");
        Java9 java9 = new Java9();
        java9.someMethod();
        java9.someMethod2();
        System.out.println("=====CLASS=====");
    }
}

=====INTERFACE1=====
override some method(public abstract)
override some method2
SomeInterface1: public static method
=====INTERFACE1=====

=====INTERFACE2=====
override some method(public abstract)
override some method2
SomeInterface2: public static method
=====INTERFACE2=====

=====CLASS=====
override some method(public abstract)
override some method2
=====CLASS=====