Why is class declared as static in Java? [duplicate]

Question

I've seen class been declared as static in java, but confused:
Since class is used to create objects, and different objects have different memory allocations.
Then what is "static" used for when declaring a class?Does it mean the member variables are all static?
Does this make sense?

Answer 1

Firstly you cannot make top-level-class static. you can only make a nested class static. By making an nested class static you basically are saying that you don't need an instance of the nested class to use it from your outer class/top-level-class.

Example:

class Outer {

static class nestedStaticClass {

//its member variables and methods (don't nessarily need to be static)
//but cannot access members of the enclosing class
}

public void OuterMethod(){
//can access members of nestedStaticClass w/o an instance
}
}

Also to add, it is illegal to declare static fields inside an inner class unless they are constants (in other words, static final). As a static nested class isn't an inner class you can declare static members here.

Can class be nested in nested class?

In a word, yes. Look at the below Test, both nested inner classes and nested static class can have nested classes in 'em. But remember you can only declare a static class inside a top-level class, it is illegal to declare it inside an inner class.

public class Test {
    public class Inner1 {
        public class Inner2 {
            public class Inner3 {

            }
        }
    }
    public static class nested1 {
        public static class nested2 {
            public static class nested3 {

            }
        }   
    }
}