자바 : Class.this

자바 : Class.this

---

이와 같은 Java 프로그램이 있습니다.

public class LocalScreen {

   public void onMake() {
       aFuncCall(LocalScreen.this, oneString, twoString);
   }
}

에서 무엇을 LocalScreen.this의미 aFuncCall합니까?

---

LocalScreen.thisthis둘러싸는 클래스를 나타냅니다 .

이 예는이를 설명해야합니다.

public class LocalScreen {

    public void method() {

        new Runnable() {
            public void run() {
                // Prints "An anonymous Runnable"
                System.out.println(this.toString());

                // Prints "A LocalScreen object"
                System.out.println(LocalScreen.this.toString());

                // Won't compile! 'this' is a Runnable!
                //onMake(this);

                // Compiles! Refers to enclosing object
                onMake(LocalScreen.this);
            }

            public String toString() {
                return "An anonymous Runnable!";
            }
        }.run();
    }

    public String toString() { return "A LocalScreen object";  }

    public void onMake(LocalScreen ls) { /* ... */ }

    public static void main(String[] args) {
        new LocalScreen().method();
    }
}

산출:

An anonymous Runnable!
A LocalScreen object

---

이 게시물은 여기 에 기사로 다시 작성되었습니다 .

---

그것은 this외부 LocalScreen클래스 의 인스턴스를 의미합니다 .

this한정자없이 작성 하면 호출이 포함 된 내부 클래스 의 인스턴스가 반환됩니다 .

---

컴파일러는 코드를 가져 와서 다음과 같이합니다.

public class LocalScreen 
{
    public void method() 
    {
        new LocalScreen$1(this).run;
    }

    public String toString() 
    {
        return "A LocalScreen object"; 
    }

    public void onMake(LocalScreen ls) { /* ... */ }

    public static void main(String[] args) 
    {
        new LocalScreen().method();
    }
}

class LocalScreen$1
     extends Runnable
{
    final LocalScreen $this;

    LocalScreen$1(LocalScreen $this)
    {
        this.$this = $this;
    }

    public void run() 
    {
        // Prints "An anonymous Runnable"
        System.out.println(this.toString());

        // Prints "A LocalScreen object"
        System.out.println($this.toString());

        // Won't compile! 'this' is a Runnable!
        //onMake(this);

        // Compiles! Refers to enclosing object
        $this.onMake($this);
    }

    public String toString() 
    {
        return "An anonymous Runnable!";
    }
}

보시다시피 컴파일러가 내부 클래스를 가져 오면이를 외부 클래스로 변환합니다 (이것은 내부 클래스를 이해하기 위해 VM을 변경할 필요가 없도록 오래 전에 내린 디자인 결정이었습니다).

When a non-static inner class is made it needs a reference to the parent so that it can call methods/access variables of the outer class.

The this inside of what was the inner class is not the proper type, you need to gain access to the outer class to get the right type for calling the onMake method.

---

Class.this allows access to instance of the outer class. See the following example.

public class A
{
  final String name;
  final B      b;
  A(String name) {
    this.name = name;
    this.b = new B(name + "-b");
  }

  class B
  {
    final String name;
    final C      c;
    B(String name) {
      this.name = name;
      this.c = new C(name + "-c");
    }

    class C
    {
      final String name;
      final D      d;
      C(String name) {
        this.name = name;
        this.d = new D(name + "-d");
      }

      class D
      {
        final String name;
        D(String name) {
          this.name = name;
        }

        void printMe()
        {
          System.out.println("D: " + D.this.name); // `this` of class D
          System.out.println("C: " + C.this.name); // `this` of class C
          System.out.println("B: " + B.this.name); // `this` of class B
          System.out.println("A: " + A.this.name); // `this` of class A
        }
      }
    }
  }
  static public void main(String ... args)
  {
    final A a = new A("a");
    a.b.c.d.printMe();
  }
}

Then you will get.

D: a-b-c-d
C: a-b-c
B: a-b
A: a

---

I know what is your confusion.I am encounter the problem just now, it should have special scene to distinguish them.

class THIS {
  def andthen = {
    new THIS {
      println(THIS.this.## + ":inner-THIS.this.##")
      println(this.## + ":inner-this.##")
      new THIS {
        println(THIS.this.## + ":inner-inner-THIS.this.##")
        println(this.## + ":inner-this.##")
      }
    }
  }
  def getInfo = {
    println(THIS.this.## + ":THIS.this.##")
    println(this.## + ":this.##")
  }
}

You can see the diff between THIS.this and this in new THIS operation by hashcode( .## )

test in scala console :

scala> val x = new THIS
x: THIS = THIS@5ab9b447

scala> val y = x.andthen
1522119751:inner-THIS.this.##
404586280:inner-this.##
1522119751:inner-inner-THIS.this.##
2027227708:inner-this.##
y: THIS = THIS$$anon$1@181d7f28

scala> x.getInfo
1522119751:THIS.this.##
1522119751:this.##

THIS.this always point to outer THIS class which is refer by val x,but this is beyond to anonymous new operation.

참고URL : https://stackoverflow.com/questions/5530256/java-class-this