Explain nested classes (or outer and inner classes) in java?, JAVA Programming

Assignment Help:

 

In Java not all classes must be described separate from each other. You may put the definition of one class under the definition of another class. The class inside class is called an inner class and the enclosing class is called an outer class. So when you prepare an inner class, it is a member of the outer class in much the similar way as other members like attributes, constructors and methods.

 

Where should we need inner classes? Code without inner classes is hard to maintainable and readable. When you use private data members of the outer class, the JDK compiler provides package-access member functions in the outer class for the inner class to use the private members. That leaves a security hole. We could avoid it using inner classes. Use inner class only when an inner class is only in the context of the outer class and/or inner class may be prepared private so that only outer class can access it. Inner classes are needed primarily to implement helper classes like Comparators, Iterators etc which are needed in the context of an outer class.

 

Member inner class

Anonymous inner class

public class MyStack {

private Object[] items = null;

...

public Iterator iterator() {

return new StackIterator();

}

//inner class

class StackIterator implements Iterator{

...

public boolean hasNext(){...}

}

}

public class MyStack {

private Object[] items = null;

...

public Iterator iterator() {

return new Iterator {

...

public boolean hasNext() {...}

}

}

}

 

Class Type

Description

Example +

Class name

 

Outer

class

Package

member class or interface

Top level class. Only type JVM

can access.

//package scope

class Outside{}

 

Outside.class

Inner

class

static nested

class or interface

Defined within the context of the

top-level class. Must be static & can access static members of its having class. No relationship between the instances of outside and Inside classes.

//package scope

class Outside {

static class Inside{       }

}

 

Outside.class ,Outside$Inside.class

Inner

class

Member class

Defined within the context of

outer class, but non-static. Until an object of Outside class has

been started you can't create

Inside.

class Outside{

class Inside(){}

}

 

Outside.class , Outside$Inside.class

Inner

class

Local class

Defined within a part of code.

Can use final local variables and final method parameters. Only

visible within the part of code that defines it.

class Outside {

void first() {

final int i = 5;

class Inside{}

}

}

 

Outside.class , Outside$1$Inside.class

Inner

class

Anonymous

class

Just like local class, but no

name is used. Useful when only one instance is used in a

method. Most naturally used in

AWT/SWING event model, Spring framework hibernate call

back methods etc.

//AWT example

class Outside{

void first() {

button.addActionListener ( new ActionListener()

{

public void actionPerformed(ActionEvent e) { System.out.println("The button was  pressed!");

}

});

}

}

 

Outside.class , Outside$1.class

 

 


Related Discussions:- Explain nested classes (or outer and inner classes) in java?

JAVA Programming, Im not in the line of computer science.But i would like t...

Im not in the line of computer science.But i would like to have some knowledge about the computer language "JAVA".I aldredy learns the computer languages "C,C++".So kindly help me

Advantages offered by soa, Advantages offered by SOA Splits down the s...

Advantages offered by SOA Splits down the silos of data, functionalities, and applications into enterprise services. Adapts an application to changing business requirements

Design patterns, what is the use of design pattern in java ?

what is the use of design pattern in java ?

Is jsp technology extensible?, YES. JSP technology is extensible by the dev...

YES. JSP technology is extensible by the development of custom actions, or tags, which are encapsulated in tag libraries. #question..

Image caching with html, In the airplane program, you may have noticed that...

In the airplane program, you may have noticed that the loading of each image appears to be jerky, erratic, or slow, and that the URL for each image flickers in the status bar each

Bluej, how to write a program to assign value of variable age and print if ...

how to write a program to assign value of variable age and print if person is major.

Corporate web support, Corporate Web Support: Worked for CGI as Sof...

Corporate Web Support: Worked for CGI as Software Engineer in a team called CWS (Corporate Web Support). We support more than 400 applications for BELL Corporate. Here tas

How can you define a readable program, How can you define a readable progra...

How can you define a readable program? A program that is easy to read & understand also easy to maintain and enhance. Readability is the ease in that text can be read and under

Nested For-Loop, I''m having trouble with creating a nested for loop to cre...

I''m having trouble with creating a nested for loop to create a table that displays every number divisible by two within the given value. For example, if the number is 8 then there

Write program for queue of cards, A Queue of Cards You are going to par...

A Queue of Cards You are going to parallel the development done in the lesson on inheritance where we constructed some base classes, StackNode and Stack, and derived  Floa

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd