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 conditional operator expression, Question: a) Change the following...

Question: a) Change the following example, using the Java's conditional operator expression, to solve the duplication problem. public class Demonstrate { public static voi

What is the difference between jsp and jsf, JSP simply gives a Page which m...

JSP simply gives a Page which may contain markup, embedded Java code, and tags which encapsulate more complicated logic / html. JSF may use JSP as its template, but gives much more

Array prints random numbers into string, Prompt the user for an int between...

Prompt the user for an int between an upper and lower boundary. Reuse the validateInput() method from project 2 to validate if the input is in bounds. If it is not, print an error

Developing a prototype system in php and javascript, General Overview A...

General Overview A number of organisations are using micro-blogging as a cost-effective way of communicating with customers, building online communities and releasing informati

Develop student portal, Develop Student Portal Project Description: T...

Develop Student Portal Project Description: Technology to be used: Java, Portlets, Liferay, functions in Oracle DB, Boostrap. We need develop two pages, a header and foote

What is color in awt, What is Color in AWT? Color is a class in the AWT...

What is Color in AWT? Color is a class in the AWT. Individual colors such as red or mauve are examples of this class, java.awt.Color. Be sure to import it if you want to use ot

Garbage collection in java, The Java programming language is object-oriente...

The Java programming language is object-oriented and includes automatic garbage collection. Garbage collection is the process of reclaiming memory taken up by unreferenced objects.

I have javascript work, I have JavaScript work Project Description: I...

I have JavaScript work Project Description: I need an annonation type tool added It should be incredible simple for a good js coder. But there will be a custom design and

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