CODEWITHSUNDEEP
javac++name-hiding
Luca
Luca

Reputation: 1776

Java nested scopes and variables' name hiding

I'm learning name look up in Java, and coming from C++ I found interesting that even if Java lets me nest however many blocks of code,I am allowed to hide a name only in the first nested scope:

// name hiding-shadowing: local variables hide names in class scope

class C {

  int a=11;

  {
    double a=0.2; 

  //{
  //  int a;             // error: a is already declared in instance initializer
  //}

  }

  void hide(short a) {  // local variable a,hides instance variable
    byte s;
    for (int s=0;;);    // error: s in block scope redeclares a
    {
      long a=100L;      // error: a is already declared in (method) local scope
      String s;         //error: s is alredy defined in (method) local scope 
    }                   
  }

}

this is weird from a C++ perspective,since there I can nest how many scopes I want,AND I'm able to hide variables as I like. Is this the normal behaviour of Java or am I missing something?

Upvotes: 2

Views: 742

Answers (2)

Suresh Atta
Suresh Atta

Reputation: 122026

I'm not a C++ guy but that really looks weird from C++ side and If I were the designer , I completely remove that behaviour. That really causes bugs and hard to read the code.

To lead a peaceful life in Java that behaviour is completely removed. Compiler shows you an error if you try to do that as you are seeing it now.

Upvotes: 3

Jon Skeet
Jon Skeet

Reputation: 1503290

It's not about the "first nested scope" - it's a matter of Java allowing a local variable to hide a field, but not allowing it to hide another local variable. Presumably the designers of Java believed such hiding to be bad for readability.

Note that your example of a local variable in an instance initializer does not create an error - this code is valid:

class C {
  int a = 11;

  {
    // Local variable hiding a field. No problem.
    double a = 0.2;
  }
}

Upvotes: 9

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