Working of this InnerClass Concept

Question

public class ShadowTest
{

    public int x = 0;

    class FirstLevel
    {
        {  // here not able to understand why it allows.

            x = 1;
        }

        void methodInFirstLevel()
        {
            System.out.println("x = " + x);
            // System.out.println("this.x = " + this.x);
            System.out.println("ShadowTest.this.x = " + ShadowTest.this.x);
        }
    }

    public static void main(String... args)
    {
        ShadowTest st = new ShadowTest();
        ShadowTest.FirstLevel fl = st.new FirstLevel();
        fl.methodInFirstLevel();
    }
}

I'm not clear why, without brackets, it doesn't work and what the significance of the brackets is? Please explain in detail.

Have a look at [this question](http://stackoverflow.com/questions/1563030/anonymous-code-blocks-in-java). — blafasel, Apr 12 '16 at 10:17
"it doesn't work" is not a problem description. In what *specific* way does it not work? — Raedwald, Apr 12 '16 at 12:00

score 1 · Answer 1 · answered Apr 12 '16 at 10:11

Because when you remove the brackets it considered as a declaration and you cannot declare the x with in the inner class again, since the outer have the variable with same name.

It is allowing with in the {} cause that considered as a initialization block when you create an instance, that executes.

score 0 · Answer 2 · answered Apr 12 '16 at 10:24

It is basically considered as a constructor there. Since you are new to java may be this will make sense to you if you write it as

public class ShadowTest {

public int x = 0;

class FirstLevel
{

    FirstLevel()     //Adding a proper costructor
    {                // here not able to understand why it allows.

        x = 1;
    }

    void methodInFirstLevel()
    {
        System.out.println("x = " + x);
        // System.out.println("this.x = " + this.x);
        System.out.println("ShadowTest.this.x = " + ShadowTest.this.x);
    }
}

public static void main(String... args)
{
    ShadowTest st = new ShadowTest();
    ShadowTest.FirstLevel fl = st.new FirstLevel();
    fl.methodInFirstLevel();
}
}

Check about constructors in here http://www.javatpoint.com/constructor

score 0 · Answer 3 · answered Jun 13 '16 at 12:23

0

If You will remove the brackets then from instance block it will become declaration state. You already have same variable x as outer class member. If you declare the variable with some other name then it could be possible.

answered Jun 13 '16 at 12:23

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Working of this InnerClass Concept

3 Answers3