Nested classes

Both Static class and Inner class are called nested class.

The purpose of a nested class is to clearly group the nested class with its surrounding class, signaling that these two classes are to be used together.

Now the 2 types:

1. Static nested classes (also: Static Classes )
2. Non-static nested classes (also: Inner Class)

Static Classes

Declare:

public class Outer {
    public static class Nested {

    }
}

Instantiate (just like a normal class):

Outer.Nested instance = new Outer.Nested();

Inner Classes

public class Outer {
    public class Inner {

    }
}

Instantiate (you MUST have an instance of enclosing class, and look weird the ‘new’ keyword looks):

Outer outer = new Outer();
Outer.Inner inner = outer.new Inner();

access level

Inner class can access private members in enclosing class (static or non-static).

public class Outer {

    private String text = "I am private!";

    public class Inner {

        public void printText() {
            System.out.println(text);
        }
    }
}

Static class cannot access non-static members.

top-level static class?

Java has no way of making a top-level class static but you can simulate a static class like this:

1. Declare your class final

2. Make the constructor private

3. Make all the members and functions of the class static

(this basically is a Singleton)