variable definitions within an interface

[Anonymous]

Hi all,
Will somebody please put me straight on the following issue ?
What are the valid modifiers for variables declared within an interface definition ?
I've read that "The only fields allowed in an interface definition are contstants that are declared both static and final" - page 113 of O'Reilly's 'Java in a nutshell'.
And yet the following simple code compiles OK ???
public interface MyInterface {
char c = 'c';
public void method1();
public void method2();
}
What am I missing, is the variable implicitly assumed to be a constant ( static final) ?
Also, how deeply does the programmer exam delve into the declaration and use of interfaces ?
Cheers, Mark.

[R K Singh]

Originally posted by Mark Lees:

1) I've read that "The only fields allowed in an interface definition are contstants that are declared both static and final" - page 113 of O'Reilly's 'Java in a nutshell'.
2) What am I missing, is the variable implicitly assumed to be a constant ( static final) ?
3) Also, how deeply does the programmer exam delve into the declaration and use of interfaces ?
Cheers, Mark.

1) that is very true.
2) Yes, in interface member variables are by default(implicitly) coderanch, static & final
if you remove initialization from your code then it won't complile.
3) I am also preparing and what i found in mock tests that it looks important point.


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Regards
Ravish

[suresh seeram]

Dear Mark Lees,
Read the following points..

All members (attributes & methods) of interface are implicitly coderanch.
All attributes defined in interface are implicitly static and final.
All methods defined in interface are NOT static.
All methods defined in interface are implicitly abstract..

All classes defined in an interface are implicitly static
Inner interfaces are implicitly static, no matter you put static modifier or not.
Outer interface are NOT static, just like outer class.

[Neha Sawant]

hi,
one small question
if a variable is defined in an interface say int value=10;
can it be used in a class that implements it in the way given below
int value=10;// i.e.redeclaring it in the class is allowed
or
int value=11;// will this give a compiler error

[Dave Vick]

Neha
If you redefine the variable in the clas that implements the interface what you'll end up doing is hiding the variable in the interface. In order to access the variabe defined in the interface you'd have to specifically access that variable.
Look at the code below:

public class Test implements MyInterface{
  int i = 11;
  public static void main(String args[]){
    Test t = new Test();
    t.printStuff();
  }
  void printStuff(){
    System.out.println(i);   // this prints the i defined in Test
    System.out.println(MyInterface.i);  // this prints the i in the interface
  }
}
interface MyInterface{
  int i = 10;
}

hope that clears it up for you.

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Dave
Sun Certified Programmer for the Java� 2 Platform