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?

Develop e-commerce website, Develop E-Commerce Website I need an E-Comme...

Develop E-Commerce Website I need an E-Commerce website for my furniture shop which requires to an online store to buy products online. So, Skills required: HTML, Java, Gr

Game, any example of games that is created by java ?

any example of games that is created by java ?

I need social mobile application, Project Description: I'm using a php s...

Project Description: I'm using a php script called phpfox on my site its work as social network . So I need is to use this script as CMS for my application. What users wil

Explain testing for equality with equals, Explain Testing for Equality with...

Explain Testing for Equality with equals? That's not what you expected. To contrast strings or any other kind of object you required to use the equals(Object o) techniques from

Illustrate RUP? , Rational Unified Process (RUP) is a normal framework ...

Rational Unified Process (RUP) is a normal framework that may be used to define a development process. The software development life cycle has got 4 parts in the following o

Explain the methods of java.lang.object, Explain The Methods of java.lang.O...

Explain The Methods of java.lang.Object? java.lang.Object gives a number of methods that are general to all objects. toString() is the most general such method. Because the def

Give the details of xml files used in validator framework, Two XML configur...

Two XML configuration files are uses by The Validator Framework validator-rules.xml and validation.xml. The validator-rules.xml shows the standard validation routines, these are re

For what purposes ftp is used in networks, For what purposes FTP is used in...

For what purposes FTP is used in networks? FTP is known as file transfer protocol it is basically used to download or upload files / data to a remote computer.

Define array, Define Array ? Indexed collections of variable of similar...

Define Array ? Indexed collections of variable of similar data types or we can say a Set of organized variables of similar type.

Which are three elements of event handler, The event handler attribute cons...

The event handler attribute consists of three elements. Write about each of them? 1. The identifier of the event handler. 2. The equal sign. 3. A string consisting of JavaScrip

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