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?

Write a java applet using swing components, The project is optional. It is ...

The project is optional. It is worth at least 7 bonus points beyond overall 100 points of this course. The grading will be on a pass/fail basis. Write a Java application (not ap

Describe remote objects?, Describe Remote Objects A Remote Object is o...

Describe Remote Objects A Remote Object is one whose functions can be called from another JVM. A remote object class must execute the Remote interface. A RMI Server is an appl

Write javascript code to scans the list of courses , In an external JavaScr...

In an external JavaScript file write code that, upon form submission, scans the list of courses for a match (case should be insensitive). If a match is found, change the div's back

Program with eclipse and enumeration , Problem Definition A new Met Of...

Problem Definition A new Met Office web application will allow users of their web site to view rainfall statistics for months and years in the UK. The application allows the m

Advantage of event-delegation over event-inheritance model, Describe advant...

Describe advantage of the event-delegation model over the earlier event-inheritance model ?

In which way java says write once run anywhere, Java says write once, run ...

Java says write once, run anywhere . In which ways this isn't quite applicable ?

Explain what is multilevel inheritance, Explain what is Multilevel Inherita...

Explain what is Multilevel Inheritance ? The Car-Motorcycle-MotorVehicle instances showed single-level inheritance. There's nothing to stop you from going next. You can describ

Describe general approaches to solve statelessness problem, Problem : (...

Problem : (a) One problem encountered when designing web applications is that HTTP is a "stateless" protocol. Describe two general approaches to solve the statelessness probl

We require expert programmers who will solve problems, We require expert pr...

We require expert programmers who will solve problems, who can code by the book, and who will code in java and JavaScript what is designed. Skills required: CSS, Java, HTML5,

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