Which of the following statements are true?
1) A class defined within a method can only access static methods of the enclosing method
2) A class defined within a method can only access final methods of the enclosing method
3) A class defined with a method cannot access any of the fields of the enclosing method
4) A class defined within a method can access any fields accessible by the enclosing method

quote:

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Originally posted by maha anna:
I came across this question in Morcus tutorial.
For sure option 2 is true(There is a typo there).For sure options 1 and 3 are wrong.
What about 4th option? I thought it is true. Because a class defined inside a method can access all local final vars defined inside the method + all final args to that method + all vars which are accessible to the enclosing method
But Morcus says ans as 1. Can anybody clarify this. I tested this 4th option with some sample code also. Am i missing something here? Can anybody clarify this?
Thank you
maha anna

Which of the following statements are true?
1) A class defined within a method can only access static methods of the enclosing method
2) A class defined within a method can only access final methods of the enclosing method
3) A class defined with a method cannot access any of the fields of the enclosing method
4) A class defined within a method can access any fields accessible by the enclosing method

[This message has been edited by maha anna (edited February 26, 2000).]

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Next - I double-checked Marcus' tutorial, specifically this part. The question as it appears there is slightly different from what Maha Anna quoted:

quote:

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Question 1)

Which of the following statements are true?

1. A class defined within a method can only access static methods of the enclosing method
   
2. A class defined within a method can only access final variables of the enclosing method
   
3. A class defined with a method cannot access any of the fields of the enclosing method
   
4. A class defined within a method can access any fields accessible by the enclosing method
   

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And so is his answer:

quote:

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Answer 1)

2) A class defined within a method can only access final variables of the enclosing method

Such a class can access parameters passed to the enclosing method

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Looking closely, he's not saying that the answer is 1); rather, he's saying that for question 1), the answer is 2). Which is probably a good argument for using letters instead of numbers for the answer options.

So, Maha Anna's version of answer 2 is false - a local class can indeed access non-final methods. (And "methods of the enclosing method" didn't really make sense anyway.)

However, I don't like the wording of Marcus' version of answer 2). The only seems vague - it's not clear exactly what is intended to be excluded. A local class can access a lot of different things, not only final variables of the enclosing method. It can not access non-final variables of the enclosing method (i.e. non-final local variables), but it can access non-local variables (i.e. class or instance fields), final and non-final, which are accessible from the enclosing method. I can't tell whether or not Marcus intended to include these in the question, but my best guess is that he forgot about them, and the statement is false.

However answer 4) is correct, as given by Maha Anna. Note that the word "field" means we're not talking about local variables, only class and instance variables. A local class can indeed access any of these which were accessible from the enclosing method. It can't access non-final local variables, but those aren't included in the statement, so the statement is true.

For anyone who isn't convinced that you can access non-final fields from a local class, try this code:

code:

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public class Test {
  private String field = "private non-final instance field";
  private void method() {
    class LocalClass {
      void method() {
        System.out.println("Look, I'm accessing a " + field);
      }
    }
    LocalClass lc = new LocalClass();
    lc.method();
    field += " again after it's been changed";
    lc.method();
  }
  public static void main(String[] args) {
    new Test().method();
  }
}

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Which prints:

Look, I'm accessing a private non-final instance field
Look, I'm accessing a private non-final instance field again after it's been changed