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?

What is methods in java explain with an example, What is Methods in java ex...

What is Methods in java explain with an example? Data types aren't much use unless you can do things along with them. For this reasons classes have techniques. Fields say what

What should be output of above code, Number = new Array(5); var abc=4; for(...

Number = new Array(5); var abc=4; for(var i=1; i { Number[i]= abc*i; } Number.reverse(); for(j=0;j { document.write(" "+Number[j]+" "); } A) What should be output of above co

Discuss features of java, Question 1 Discuss features of JAVA Question...

Question 1 Discuss features of JAVA Question 2 What are primitive data types? Discuss Question 3 Explain data conversion function ValueOf ()? Question 4 What are th

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..

Javascript, You can declare a variable by the var statement such as: var...

You can declare a variable by the var statement such as: var strname = some value You can also declare a variable with simply assigning a value to the variable. Although, if

What is includeaction, The IncludeAction class is useful when you require t...

The IncludeAction class is useful when you require to integrate Struts into an application that uses Servlets. Use the IncludeAction class to contain another resource in the respon

Develop android geolocation service app, Project Description: Develop an...

Project Description: Develop an android service app that will run on the background. The app has to get the users location (longitude and latitude) every 5 minutes or when th

How many static initializers can there, How many static initializers can yo...

How many static initializers can you have ? As many as you want, but the static initializers and class variable initializers are implemented in textual order and may not refer

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