Why inner classes cannot have static declarations ?

Question

Hi Friends,
When i tried to make static declarations on a inner class which is non static, i am getting compilation error saying "inner classes cannot have static declarations". I want to know reason behind this implementation.
Code which i have tried:
public class TestOuter
class TestInner{
static int i =10;
public static boolean validate(int a){
if(a==0)
System.out.println("Invalid data");
return false;
return true;
public static void main(String a[]){
boolean result = new TestOuter.TestInner.validate(0);
System.out.println("Result="+result);
Thanks,
Shiju V.

Answer 1

so I think if the
outer class is not static , then Inner class can't be
static as well. This is incorrect. An enclosed class can be indeed static while the outer is not, and vice versa.
The difference between static/non static in regards to enclosed classes is that the static ones are 'top-level' and cannot access the members of the enclosing class.
The effect of making an enclosed class static means there is only one instance of any variables, no matter how many instances of the outer class are created. In this situation how could the static inner class know which variables to access of its non static outer class. Of course the answer is that it could not know, and thus an static inner class cannot access instance variables of its enclosing class.
Now, regarding non-static inner classes, and trying to give a valid answer to the original post:
As with instance methods and variables, a non-static inner class is associated with an instance of its enclosing class and has direct access to that object's instance variables and methods.
TestOuter outer = new TestOuter();
TestOuter.TestInner inner = outer.new TestInner();Because an inner class is associated with an instance (inner class implicitly keeps a reference to the object of the enclosing class that created it), it cannot define any static members itself. Static members cannot access the this pointer.
So, in an ordinary (non-static) inner class, the link to the outer class object is achieved with a special this reference. A static inner class does not have that special this reference, nor would a static method/variable of an ordinary (non-static) inner class.