About Question enthuware.ocpjp.v7.2.1726 :

[PtFyEH]

To access Onion's data inside Layer, you can do Onion.this.data.

Explanation could be extended to:

To access Onion's data inside Layer, you can do Onion.this.data or super.data.

[admin]

Why do you think so?

[sumanenthu]

I understood your point? But why can't it return "thegoodpart"?

[admin]

It does print "thegoodpart".

[TejWidJava]

After removing getData() in Inner Layer classs why its giving StackOverflowError?

Its very strange.

[admin]

If Layer's getData is not present, Onion's getData() will be invoked, which calls return new Layer().getData(); This is basically an unending recursive call. Hence the error.

[jagoneye]

If Layer's getData is not present, Onion's getData() will be invoked, which calls return new Layer().getData(); This is basically an unending recursive call. Hence the error.

What is the reasoning behind this method call? How can the innerclass access outer class's instance method? Accessing outer class variables is fine! But this is something out of the worlD! And that too without returning an actual String it still compiles!

[admin]

If Layer's getData is not present, Onion's getData() will be invoked, which calls return new Layer().getData(); This is basically an unending recursive call. Hence the error.

What is the reasoning behind this method call? How can the innerclass access outer class's instance method? Accessing outer class variables is fine! But this is something out of the worlD! And that too without returning an actual String it still compiles!

Why do you think accessing outer class variables is different from accessing outer class methods? Both are members. Access rules should apply equally to both.

[jagoneye]

That was my first guess! Thanks!

[lucastomasini]

If Layer's getData is not present, Onion's getData() will be invoked, which calls return new Layer().getData(); This is basically an unending recursive call. Hence the error.

What is the reasoning behind this method call? How can the innerclass access outer class's instance method? Accessing outer class variables is fine! But this is something out of the worlD! And that too without returning an actual String it still compiles!

Why do you think accessing outer class variables is different from accessing outer class methods? Both are members. Access rules should apply equally to both.

Layer class can access getData() method of Onion class because Layer is extending Onion, thus it inherits getData(), but not because it is an inner class of Onion. Actually, if you remove getData() from Layer and the "extends Onion" from Layer class definition, the code will not compile.

class Onion {
private String data = "skin";
private class Layer {
String data = "thegoodpart";
}
public String getData() {
return new Layer().getData(); // "Cannot resolve method getData()"
}
public static void main(String[] args) {
Onion o = new Onion();
System.out.println(o.getData());
}
}

[admin]

>>new Layer().getData(); // "Cannot resolve method getData()"
This will indeed not compile because Layer's doesn't have getData. Onion Does. Layer can access Onion's getData. So the following compiles even if you remove extends Onion and getData method from Layer -

public void getX() {
System.out.println(getData()); //uses Onion's getData
}

[lucastomasini]

>>new Layer().getData(); // "Cannot resolve method getData()"
This will indeed not compile because Layer's doesn't have getData. Onion Does. Layer can access Onion's getData. So the following compiles even if you remove extends Onion and getData method from Layer -

public void getX() {
System.out.println(getData()); //uses Onion's getData
}

You are absolutely right, I missed that.

Thanks!