Use of j2se internal classes

Java has four internal classes:

1. static inner class: only static member variables and static methods of external classes can be accessed. The method for generating static internal class objects is as follows:

Outerclass. innerclass inner = new outerclass. innerclass ();

Example:

Public class staticinnerclass {
/**
* Use of static internal classes
*/
Public static void main (string [] ARGs ){

Staticinner. Inner inner = new staticinner. Inner ();
Inner. Test ();
}
}
Class staticinner {
Public static int A = 5;

Public static class inner {
Public void test (){
System. Out. println ();
}
}
}

2. Member internal class (member inner class): the static and non-static objects and methods of the external class can be accessed. The method for generating static internal class objects is as follows:
Outerclass. innerclass inner = new outerclass (). New innerclass ();

Example:

/**
* Member internal class
*/
Public class memberinnerclass {
Public static void main (string [] ARGs ){
Memberinner. inner2 inner2 = new memberinner (). New inner2 ();
Inner2.dosomething ();
}
}

Class memberinner {
Private int A = 4;
Public class inner2 {
Private int A = 5;
Public void dosomething (){
System. Out. println (memberinner. This. );
}
}
}

To access the member variables of an external class in a local internal class, the syntax is: outerclass. This.

3. Local inner class)

Defined in a method, only final variables declared in the method can be accessed.

Example:

Public class localinnerclass {
/**
* Local internal class
*/
Public static void main (string [] ARGs ){
Localinner inn = new localinner ();
Inn. dosomething ();
}
}

Class localinner {
Public void dosomething (){
Final int A = 4;
Class inner3 {
Public void test (){
System. Out. println ("Hello World ");
System. Out. println ();
}
}
New inner3 (). Test ();
}
}

 

4. Anonymous internal class (anonymous inner class) (most used)

An anonymous internal class implicitly inherits a parent class or implements an interface.

Example:

Public class anonymousinnerclass {
/**
* Anonymous internal class
*/
Public static void main (string [] ARGs ){
Anonymousinnerclass AIC = new anonymousinnerclass ();

String STR = AIC. getdate (new date (){});
// Generate an object that inherits the subclass of the date class
System. Out. println (STR );
}

Public String getdate (date ){
Return date. tolocalestring ();
}
}