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 {
}
}
}
}
