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?

Functions in javascript, The following set of short questions will focus on...

The following set of short questions will focus on getting you familiar with JavaScript functions. All functions and testing should appear in a single XHTML 1.0 Strict page. All

Program to change base system, Write a program called BaseConverter that pr...

Write a program called BaseConverter that prompts (asks) the user for a base 10 number and another number, between 2 and 10 inclusive. This second number is the base to which to co

What is portableremoteobject.narrow() method , What is PortableRemoteObject...

What is PortableRemoteObject.narrow() method and what is used for?                Ans) Java RMI-IIOP gives a mechanism to narrow the the Object you have received from from your

Java web services, #quThis project is based on the teams example of chapter...

#quThis project is based on the teams example of chapter 1. Instead of teams, you will consider employees working in a department in a company. (Departments and employees are ana

Explain the coordinate system, Explain the Coordinate System? Java uses...

Explain the Coordinate System? Java uses the standard, two-dimensional, computer graphics coordinate system. The first visible pixel in the upper left-hand corner of the applet

Describe about basic java programming language, Describe about basic java p...

Describe about basic java programming language? 1. Study the Java programming language: its syntax, patterns, idioms, and styles. 2. Become comfortable along with object orien

Code, Write a programme to create a webpage that prints the name of the STU...

Write a programme to create a webpage that prints the name of the STUDENT database in Wide Latin font and set the subtitle with description of the STUDENT to the screen. Set the pa

Development build to production server tomcat, Move development build to pr...

Move development build to production server tomcat Project Description: Move our development build and integrate with MYSQL database, to our production vps. The software i

Make a function in java script and compare with ten, Write JavaScript code ...

Write JavaScript code for the following: Make a function compare With Ten (value) Compare the function argument along with ‘10' and display a message while the value is le

How virtual communities are formed, How virtual communities are formed? How...

How virtual communities are formed? How these are different from other Communities? Give examples. Virtual Communities are interest-based communities. Members along with genera

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