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?

Project, Prog. Concepts - Project The objective is to implement a menu - ba...

Prog. Concepts - Project The objective is to implement a menu - based system for Bank Accounts in order to simulate a very simple banking system. Many structures have to be declare

Explain about java sdk, Java SDK is not so comfortable with people used to ...

Java SDK is not so comfortable with people used to command line interpreter. IDEs contain compilers, editors, debugging facilities, drag and drop methods, etc. This compiler strive

Program to create shipping company model, This assignment models a simplifi...

This assignment models a simplified delivery company. It is composed of the following departments:  receiving which contains a list of packages to be delivered, shipping which ship

Java Project, How to start a java project? how to draw a flow chart?

How to start a java project? how to draw a flow chart?

How are this () and super() used with constructors, How are this () and sup...

How are this () and super() used with constructors? this() Constructors: is used to pointing current class instance. Can be used with methods or variables. Used to call

Javaserver faces (jsf) framework, JavaServer Faces (JSF) framework : Ja...

JavaServer Faces (JSF) framework : JavaServer Faces is a new framework for creating Web applications using Java. JSF gives you with the following main features: Basic us

A session facade? , Too many function invocations between the server and th...

Too many function invocations between the server and the client will lead to network overhead, tight coupling due to dependencies between the server and the client, misuse of serve

Java program to play minesweeper , Project Requirements Write and tes...

Project Requirements Write and test a Java program to play Minesweeper using Model-View-Presenter design (The model is an interface defining the data to be displayed or other

Online Music Store, Online music store that stores information about song, ...

Online music store that stores information about song, artist, album, customer, playlist. Also all necessary diagrams - use case, uml, erd

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

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