interface reference variable

[Ayub ali khan]

Could any one clear the following doubt?

Can we assign a null reference to a local variable which refers to an interface?

Thank you.

[Ernest Friedman-Hill]

Yes.

Moving to Java in General (Beginner).

[marc weber]

Originally posted by Ayub ali khan:
Could any one clear the following doubt? Can we assign a null reference to a local variable which refers to an interface? ...

Have you tried this? What happened?

[Ayub ali khan]

Thank you Ernest and Marc.

I am using Eclipse and it prompts me to initialize the variable which refers to an interface. I have an option to click initialize. When I do that its being initialized to null. I thank Ernest for giving an instant answer to this question (before I could realize the feature of Eclipse).

Sorry for a delayed response.

Thank you for all your assistance.
[ February 28, 2006: Message edited by: Ayub ali khan ]

[Anonymous]

Learn by Example:
First of all, without initializing, you cannot use any kind of Object-Reference; this is not just for Interfaces.

Example:
java.io.Serializable is an interface

        Serializable ser ;
        if (ser == null){
            // do sth
        }    

not;
but this will compile and work:

        Serializable ser ;
        if ((ser= null) == null){
            ser = new Class-Implementing-Serializable();
               ...
        }    

[Aum Tao]

Isn't the reference initialised automatically to null, if not done explicityly, just like primitive data types?

[Ernest Friedman-Hill]

Originally posted by Aum Tao:
Isn't the reference initialised automatically to null, if not done explicityly, just like primitive data types?

Only member variables are automatically initialized. Local variables (those defined inside a method or code block) are not.

[ak pillai]

you cannot use any kind of Object-References without initializing. Instance (aka member) variables are implicitly initialized when the object is created in the heap but the local variables are not in the stack.

Concept:

Each time an object is created in Java it goes into the area of memory known as heap (i.e instance variables also). The primitive variables like int and double are allocated in the stack, if they are local method variables and in the heap if they are member variables (i.e. fields of a class). In Java methods local variables are pushed into stack when a method is invoked and stack pointer is decremented when a method call is completed.

[Robert Hill]

Even if you have an explicit constuctor that does not initialize all member variables?

[Ken Blair]

Originally posted by Robert Hill:
Even if you have an explicit constuctor that does not initialize all member variables?

Yes.