Chapter8

Un article de Sometimes Kitties Think Too.

SCJP

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Chapter 8 - "Inner Classes"

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Types of Innner Classes

1) regular inner class

2) method-local inner class

3) anonymous 

       + subclass
       + implementor

4) static nested class

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Rules

  • Regular inner classes cannot have static declarations. Must have an instance of the outer class.
  • Modifiers

You can use the same modifiers for inner classes that you use for other members of the outer class. For example, you can use the access specifiers — private, public, and protected — to restrict access to inner classes, just as you do to other class members.

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Constructing Inner Classes

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Non-static Inner Class (Nested)

class OuterClass {
...
static class StaticNestedClass {
...
}
class Non-StaticInnerClass {
...
}
}
  • non-static method constructing an instance of the nested class: 
       Inner x = new Inner();


  • Syntax for instantiating an inner class externally: 
       new MyOuter().new MyInner()
  • How to construct an instance on a nested class where either no "this" object exists, or the current this object is not an instance of the outer class: 
       Outer.Inner y = new Outer().new Inner();
               
                  OR

       Outer x = new Outer();
       Outer.Inner y = x.new Inner();
  • How to create an instance of a static inner class 
       Outer.Inner I = new Outer.Inner();
  • Regular Inner classes are scoped at the same level as instance variables
  • Inner classes have access to member variables and methods of the containing class
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Method Local Inner Classes

  • In addition, Method-local inner classes cannot use the local variables of the method that the inner class is in. Only if they are declared /final/
  • Must instantiate an inner class within the method below the definition if you want to use it.
  • All modifiers apply to inner and method-local inner classes (abstract, final, private ...)


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Anonymous Inner Classes

  • Anonymous classes are either subclasses or implementors
  • Anonymous classes do not inherit the superclass methods that they do no override
  • Inner classes can access all members of the outer class, even the "private" ones 
      Except static nested classes do no have access to non-static methods/variables of the outer class
  • anonymous inner classes do not have constructors 



class ThisIsAnAnonymousClass {
	
	void f() {
		System.out.println("F method");
	}
	
	void g() {
		System.out.println("G method");
	}
	
}

.....in another class.....

		inner.classMethod(new ThisIsAnAnonymousClass() 
			       { 
				  void f() 
				  { 
				      System.out.println("I'm doing my own thing!"); 
				   }
				}
		);


Scope
Type Scope Inner
static nested member no
inner (non-static) member yes
method local local yes
anonymous only where defined yes

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