Inner class usage

[shyam prasad nandigam]

can any one give a real time example, where inner classes are exactly used...
please

[Welly Tambunan]

I've just reading this article. I think this one si related to your question. Hope that's help

http://www.javaspecialists.eu/archive/Issue002.html

[Arka Guhathakurta]

Hi,
Good Question. Generally inner classes are used to create anonymous local classes.For example someone wants to create a Thread object and pass a Runnable object in it.
Ex:

  
public static void main(String...args){
Thread th = new Thread(new Runnable()
{
 public void run()
 {
  System.out.println("Overloaded run);
 }
});
}                                                    

The code is a bit complex to look at but you can create thread objects like this without even needing to implement Runnable.Another important usage of inner classes is in awt events. Inner anonymous classes come of great use while designing complex action events.

[Stephen Davies]

Inner classes are also frequently used for adding action and event listeners, for example in a Swing application (e.g. a button). This then reduces the need for one action performed method to have to check which button was pressed and assigning the relevant action.

[Kavita Tipnis]

Inner classes can be used to do quite a great deal of stuff on the fly.
I wrote some quick code to see if they can be used to compare objects on the fly.
(Try it out as a mock question!)

public class InnerClassEx {

    public InnerClassEx(){
        list1.add("1");
        list1.add("2");
        list1.add("3");
        list2.add("1");
        list2.add("2");
        
     }
    
    private ArrayList<String> list1=new ArrayList<String>();
    private ArrayList<String> list2=new ArrayList<String>();
    
    public class NormalInner implements Comparator<String>{
        NormalInner(){
           System.out.println("Normal Inner Class --Constructor"); 
        }
     public int compare(String a,String b){
         return a.compareTo(b);
     }   
    }
    
    public void myMethod(){
        final int x=10;
        class MethodInner{
            MethodInner(){
                System.out.println("Method Local Inner Class --Constructor");
                System.out.println("Value of x="+x);
            }
        }
       MethodInner mInner=new MethodInner();
       
    }
    
    public static void main(String[] args){
        final InnerClassEx ex=new InnerClassEx(); //ex declared final for access to anonymouse class
        InnerClassEx.NormalInner norm=ex.new NormalInner();
        System.out.println("Comparing elements in arraylist in inner class="+norm.compare(ex.list1.get(0),ex.list2.get(1)));  
        ex.myMethod(); 
        Comparable comp=new Comparable<ArrayList><String>>(){    //creates an anonymous class which implements a comparable interface
            public int compareTo(ArrayList<String> myList){
                return(ex.list1.get(0).compareTo(myList.get(0)));
            }
           
        };
        System.out.println("Anonymous Inner Class----");
        System.out.println("Comparison in anon class"+comp.compareTo(ex.list2));
    }

[Tim McGuire]

thanks for contributing this example.

that should be:

Comparable comp=new Comparable<ArrayList<String>>(){    //creates an anonymous class which implements a comparable interface

on line 41

(it looks like the forum code alters it when I paste it in here.
here is the string I'm trying to paste:

Comparable comp=new Comparable<ArrayList<String>>(){ //creates an anonymous class which implements a comparable interface

here is how it looks after submission

Comparable comp=new Comparable<ArrayList><String>>(){ //creates an anonymous class which implements a comparable interface

[Kavita Tipnis]

Yes, I tried to edit it but I could not.

[shyam prasad nandigam]

thanks to one and all who reacted to my question and gave answers..
now i got a clear idea of inner classes and where they are used...
once again thank you very much to all