Nested Classes

HadjshellAbout 1 minNoteLanguageJava

Place a class definition within another class definition
Nested classes are divided into two categories: non-static and static
- Non-static nested classes are called inner classes
- Nested classes that are declared static are called static nested classes

Inner Classes

Inside the outer class, inner class can access the members of outer class directly (even if it's private)
Inside the outer class, you can create inner class objects
If you want to make an object of the inner class anywhere except from within a non-static method of the outer class, you must specify the type of the object as Outer.Inner
```
// Inner class is public
Outer outer = new Outer();
Outer.Inner inner = outer.new Inner();
```
Produce the reference to the outer class object within the inner class definition: Outer.this
The inner class will be compiled to Outer$Inner.class
Inner class cannot have static members or nested classes

Local inner class: an inner class defined inside a code block, typically in a method
- A local class can access local variables and parameters of the enclosing block that are final or effectively final
Anonymous inner class: an inner class defined at the time of creation of itself
- In other words, we can say that it a class without the name and can have only one object that is created by its definition
- Useful when you want a class inheriting from a superclass or implementing an interface which only used in a specific method
- ```
interface Eatable {
 	void eat();
}
class TestAnnonymousInner1 {
   public static void main(String args[]) {
   		Eatable e = new Eatable() {
    		public void eat() {System.out.println("nice fruits");}
   		};
   		e.eat();
   }
}
```

The static member of outer class
In effect, a static nested class is behaviorally a top-level class that has been nested in another top-level class for packaging convenience
You instantiate a static nested class the same way as a top-level class
```
StaticNestedClass staticNestedObject = new StaticNestedClass();
```