why inner classes in java cant have static elements?

Question

class Outerclass {
    
    class Innerclass {
        public static int var=10;
    }
    
    public static void main(String[] args) {
        System.out.println("hello world");
    }
}

I know that inner class object has to be associated with object of outer class so it cant have static members, but I don't really understand it. Can anyone please elaborate on that? this code gives error as we are declaring static variable in an inner class....

Answer 1

In Java, an inner class is implicitly associated with an instance of its outer class. This means that an inner class object is tied to an instance of the outer class. Because of this association, it’s not allowed to declare static members in an inner class.

Static members belong to the class itself, rather than to any individual instances of the class. If an inner class could have static members, it would violate the inherent association between the inner class and the instance of the outer class.

However, there is an exception for compile-time constant fields. These can be declared as static in an inner class because they are final and initialized with a compile-time constant expression.

If you need to use static members within an inner class, consider using a static nested class. Unlike an inner class, a static nested class doesn’t require an instance of the outer class. It’s more like a regular class that just happens to be nested within another class for packaging convenience.