Accessing instance variable inside static reference.

[Prakash Rai]

class A{
       int  a=10;
}
public class B{
public static void main(String arg[]){
A a1=new A();
System.out.println(a1.a);  //How can I access instance variable inside static context.
}
}

Q1.Here variable int a is instance variable and main method is static . so How can I access instance variable inside static context?

[Mohamed Sanaulla]

You are accessing the instance variable via the instance which is perfectly fine.

And Suppose a1 was declared at the class level- Instance variable then the current usage would have given an error- a1 is being referred in a static context

[pete reisinger]

maybe it is confusing for you because the code is inside static method, but you are creating instance, and calling method on that instance, you are not just calling method (which wouldn't be possible)

[Prakash Rai]

Thanks pete reisinger...
Can you give me another example of this.?

[Campbell Ritchie]

It would be better for you to try such an example, and show us it.

[mike ryan]

   1. class A{  
   2.        int  a=10;  
   3. }  
   4. public class B{  
   5. public static void main(String arg[]){  
   6. A a1=new A();  // here you have created a new A object withe the name a1
   7. System.out.println(a1.a);  //---->a1.a is using the object reference a1 to access the object which is allowed and works
       // this wouldn't be allowed
      System.out.println(A.a); // because you can't access the object directly from this static context.
 
   8. }  
   9. }  

Hi, I commented on some parts of your code to explain maybe a bit better.Hope it helps you understand better!

[Sean Clark]

This is more the example you need:

public class B{
    int a = 10;

    public static void main(String arg[]){
        B b1=new B();
        System.out.println(b1.a);  //calling instance variable a from an instance this is fine
        System.out.println(a);  //calling instance variable a from a static context, not allowed
    }
}

Hope this helps a bit.

Sean

[Prakash Rai]

Thanks to all ...

[Campbell Ritchie]

mike ryan wrote:

 . . .
      System.out.println(A.a); // because you can't access the object directly from this static context.
 . . .

Hi, I commented on some parts of your code to explain maybe a bit better.Hope it helps you understand better!

Not convinced. The reason access is denied is that you are trying to use an instance member of class A as if it were a static member. If you tried that inside an instance method, like this . . .

public class A
{
   int a = 10;
}

public class B
{
   public int foo()
   {
      return A.a; // Trying to access an instance field on the name of the class. Only works for static members
   }
}

. . . you would suffer the same compiler error. Sean Clark's example answers the original question better.