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default value for object refernce

sai donthneni
Ranch Hand

Joined: Mar 26, 2006
Posts: 50
What is the default value for an object refernce. Is the null a default value for these refernce variables. What if an object is instantiated and it has no constrcutor... Is the default value null?

When you use that refernce varaible to the left of instanceof operator with the Object on the right side of the operator. Will it produce false?
Paul Clapham

Joined: Oct 14, 2005
Posts: 18541

The default value for a variable that can contain an object reference is null. But your question "What if an object is instantiated and it has no constrcutor" doesn't mean anything. You can only instantiate an object by calling one of its constructors, and it isn't possible for a class to not have any constructors.

And your other question is what does "null instanceof Object" return? I will leave you to write a one-line test program for that.
marc weber

Joined: Aug 31, 2004
Posts: 11343

All classes have a constructor. If none are explicitly written into the class definition, then a default no-args constructor is provided by the compiler.

Class/instance variables for non-primitive types are automatically initialized to null. However, local variables (e.g., declared within a method) must be explicitly initialized before they are used or a compiler error will result.

As for "null instanceof ..." See JLS 15.20.2.

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