Difference between abstact class and interface

hi
i am new in java.
plz tell me abstract class support which type of polymorphisam and
interface support which type of polymorphisam
plz explain
bye
siva

There's only one type of polymorphism.
Does that make it mono-polymorphism? ;)
Indeed - do a search for the forums.
The short answer is that both abstract classes and interfaces define required method signatures for subclasses that extend/implement them, but abstract classes can have implementation for some or all methods that are not abstract; interfaces have no implementation whatsoever for any methods.

Similar Messages

What is the difference between Abstract class and Interface ?

Hi,
Could u plz tell me the difference between Abstract class and Interface?
Thanks in advance.
Gopi

Lots.
An abstract class can contain some method implementations, or indeed all the method implementations. It may contain methods with all the various access modifiers. It cannot be instantiated. A class may inherit from only a single abstract class.
An interface contains only public method stubs and constants. A class may implement multiple interfaces. An interface cannot (obviously) be instantiated.
Abstract classes are particularly useful when you need to provide a semi-complete implementation for reuse. Interfaces are used more like types.
Look at java.util.* for some good examples of the use of both.

Difference between Abstarct Class and Interface

HI,
Here is a simple one for the gurus but quite important for me.
What is the difference b/w an Interface and an abstract class?
Why do we need each one of them?
I would appreciate if you people can give examples of each so that I amy understand fully
Thanks in advance...

A normal class (not abstract) has a special behaviour, like java.awt.Frame. A Frame is a frame no matter how you subclass it. If you create a subclass it will still be able to be displayed by calling it's show method. So by using a normal class you can create a type of class.
An abstract class does the same, but it leaves some of the code unwritten. For instance java.lang.Number. This class is abstract becuase it has no knowledge of how to store the number in memory. But it knows that it is a number, and any subclass will still be a number. You could create a subclass of Number that can hold the time in milliseconds and checks your system clock to see what the time is, it could also have methods that return the time in another country, but it would still be just a Number.
An interface is a way to describe what an object can do, not what it is. So with java.lang.Comparable as an example you can make any class comparable. This means that no matter what type of object you have, it can be compared with other objects. So you can have a subclass of Frame that can be compared with other windows. Or a subclass of Number that can be compared with other Numbers. You can even compare those two different types if you like. So you could compare a window with a number.
That is the difference between abstract classes and interfaces.
I hope you could follow my arguments, it isn't an easy subject,
Daniel

Difference between abstract classes and interfaces

I actually wonder about what are the differences between abstract classes and interfaces may somebody give an example code about it?
and i have one more question how can i use interfaces like multiple inheritance ? i mean when i implement an interface like
class a extends b implements c,di have to use all c and d methods but what that methods means?
I mean as i know we cannot make implementations of methods in interfaces
but for example in runnable interface there is a method like run() and it has been defined somewhere because it knows what to do(i mean when it will run), i just write my code into that method .

Once you get past the starting point (I am referring to the OP here), there are a few salient differences:
You can only extend (or generalize) a single superclass; however, you can implement (or realize) multiple interfaces. As such, all things being equal, using an interface in lieu of an abstract class 'frees' your design. Later, if you want the implementor of an interface to inherit from another class, there is not issue.
Any abstract method specifies a contract. However, abstract classes allow you to also add common behavior to subclasses. This is an overused justification for abstract classes, IMO. You can achieve the same effect using delegation and still having interfaces.
Always program to interfaces wherever possible. This means that you define an interface and have an implementing class (usually at a minimum). Do not do this for all your classes, but rather the ones that make your system unique (the domain model or M in MVC architecture). This allows you to later change implementation with a minimal amount of refactoring. This is a core precept from the Group of Four and any number of decent programming books.Best of luck.
- Saish

Difference between abstract class and interface

Hi everyone,
CAn anyone explain why the following happen????
Abstract class can have a constructor, Interface cannot.
Abstract class can have static methods, Interface cannot.

What are the advantages of defining constant
variables in Interfaces?Not many.
Effective Java - Joshua Bloch, Chapter 4, Item #17: Use interfaces only to define types.
The constant interface pattern is a poor use of interfaces. That a class uses some constants internally is an implementation detail. Implementing a constant interface causes this implementation detail to leak into the class's exported API. It is of no consequence to the users of a class that the class implements a constant interface. In fact, it may even confuse them. Worse, it represents a commitment: if in a future release the class is modified so that it no longer needs to use the constants, it still must implement the interface to ensure binary compatibility. If a nonfinal class implements a constant interface, all of its subclasses will have their namespaces polluted by the constants in the interface.
In summary, interfaces should only be used to define types. They should not be used to export constants.

What's the difference between Abstract Class and Interface?

Dear all,
Can anyone give me some hints about this topic?
Thanks.
Leo

an abstract class may have some methods already implemented in the abstract class but an interface has no methods implemented
I think it's just that simple.
For your design needs, you just choose what you need : )
Cheers
Stephen

Difference between Abstract Classes Vs Interface

Hi,
Can u pls mention all the differences between Abstract Classes and Interface.? I've mentioned the differences I've known here.
Known Differences:
(*) An interface cannot implement any methods, whereas an abstract class can.
(*) A class can implement many interfaces but can have only one superclass
Can U pls mention at what situation(practical situation) we've to go for abstract class or Interface?
Tell me the situation when we have to go for abstract class?
Tell me the situation when we have to go for interface?
Please Reply me
Thanks & Regards
Venkatesh

There are more differences, and one really important is that abstract classes can also define class variables, while interfaces cannot. I think the question of when to use interfaces or abstract classes is not always easy to answer, but yourself have pointed some tips you should be aware of :
If you need that some funcionality of the class is derived by more than one "parent" then you should use interfaces, since you cannot extend more than one class.
If your "superclass" needs to define some class variables then the choice must be made to have a superclass and then extend it. Also this is applicable if there is a method that can be programmed at a higher level (in interfaces you cannot program methods).
But the answer to the question is still not easy. And remember, you can always mix both tipes, you can extend one class and implement some interfaces.
Examples or that are very common in the Java API for AWT or Swing components, for example javax.swing.JLabel extends javax.swing.JComponent (that is beacuse a JLabel IS a JComponent and it uses some variables and methods programmed at the JComponent "level") and it also implements some interfaces: Accessible, ImageObserver, MenuContainer, Serializable & SwingConstants.
I hope this helps.
Zerjillo

What is the difference between document class and normal class

Hi,
Please let me know what is the difference between document class and normal class.
And I have no idea which class should call as document class or call as an object.
Thanks
-Actionscript Developer

the document class is invoked immediately when your swf opens. the document class must subclass the sprite or movieclip class.
all other classes are invoked explicitly with code and need not subclass any other class.

Difference between Conversion progs and INTERFACES

Hi plz tell me ...
whats the difference between Conversion progs and Interfaces in ABAP .
wat are conversion progs ( exmple) and interfaces ( exmple ) ?
thnks in advance....

Hi
CONVERSION programs are the ones which have one time usage, usually when a legacy system is being replaced by a system like SAP, then the data has to be mapped from the legacy system to SAP system. Here the data to be converted is given on a flat file & is uploaded to SAP tables mostly using LSMW only. Conversions programs are BDC,BAPI and LSMW programs in which you upload all the related tables from the flat files.Those are one time programs.
Interface programs are those programs in which you fetch the data from the application server and process on theose data.These are helpful when you have to run any program in the backgroup when the presentation server is not working.
INTERFACE programs are the ones which are run at regular intervals, say weekly, monthly or even daily. Here the legacy system continues to co-exist along with SAP system, the legacy system might be useful for certain functionalities but the data might have to run thru SAP transactions for complex data maintenance at regular intervals.
In Simple
CONVERSIONS : Converting Legacy System DATA into a flat file
INTERFACES : Converting Flat File into SAP
Conversion Program
http://help.sap.com/saphelp_erp2005/helpdata/en/d3/a65a14e96911d1b401006094b944c8/frameset.htm
Interface Program
http://help.sap.com/saphelp_erp2005/helpdata/en/64/be5b4150b38147e10000000a1550b0/frameset.htm
<b>Reward if usefull</b>

Difference between Data Class and Delivery Class

What is the Difference between Data Class and Delivery Class , what happens Phisically to the Data .
Moderator message: what is the difference between your question and a question that we'd welcome here in the forums?
[Rules of engagement|http://wiki.sdn.sap.com/wiki/display/HOME/RulesofEngagement]
Edited by: Thomas Zloch on Nov 22, 2010 1:17 PM

What is the Difference between Data Class and Delivery Class , what happens Phisically to the Data .
Moderator message: what is the difference between your question and a question that we'd welcome here in the forums?
[Rules of engagement|http://wiki.sdn.sap.com/wiki/display/HOME/RulesofEngagement]
Edited by: Thomas Zloch on Nov 22, 2010 1:17 PM

Difference between functional task and interface task

Hi All,
Kindly let me know the Difference between functional task and interface task when we create a task profile.
Regards,
Swetha

Hi Sweta,
The diferennce is Like we create different roles like store incharge and Store manager for Store manager there are list of activities that he can do like approve requests from store keeper and so on so these are Interface tasks as there are differences based on the roles of the employee but if a person can only create and not approve the transation then this is functional task difference

Difference between Material Class and Batch Class

Hi!
What is the difference between Material Class and Batch Class?
and how can we use these classes?
Rgds,
Ajit

Iam not sure but i think
1) Material class for sorting purpose
2) Batch Class for Batch Management
thanks
K.Prabakaran

Difference between Java class and JavaBean?

What is the difference between a Java class and a JavaBean?
A class has variables which hold state.
A class has methods which can do things (like change state).
And if I understand a JavaBean it is rather like a BIG class...
i.e.
A JavaBean has variables which hold state.
A JavaBean has methods which can do things (like change state).
So, what's the difference between the two?
And in case it helps...What is the crossover point between the two? Is there a minimalist type JavaBean which is the same as a class? What is the difference between Java beans and Enterprise Java Beans?
Thanks.

Introspection, as I understand it is a bunch of
methods which allows me to ask what a class can do
etc. right? So, if I implement a bunch of
introspection methods for my class then my class
becomes a JavaBean?Introspection allows a builder tool to discover a Bean's properties, methods, and events, either by:
Following design patterns when naming Bean features which the Introspector class examines for these design patterns to discover Bean features.
By explicitly providing the information with a related Bean Information class (which implements the BeanInfo interface).
I understand now they are completely different.
Thanks. Very clear.
I do not understand how they are completely different.
In fact I don't have a clue what the differences are
other than to quote what you have written. In your
own words, what is the difference? This is the "New
to Java Technology" forum ;-) and I'm new to these
things.In that case ejbs are way too advanced for you, so don't worry about it.

Difference between static class and singleton?

Hi I wonder what could be the difference between static methods and singleton?
In singleton at any point of time there will be only one object existing in the JVM. We create singleton to avoid multiple object creation for that class.
If I make all the methods in the class as static also it does the same job. The memory will be allocated once. Even there wont be any object in this case, so time required for object creation also can be saved. looks like more efficient but still why need singleton?
This question is also posted in java programming forum. The thread is as follows:-
[Click on this to visit that thread |http://forum.java.sun.com/thread.jspa?threadID=5278517&tstart=0]
Edited by: murrayb9654 on Mar 25, 2008 8:20 AM

yawmark wrote:
Static class is a realization of singleton pattern.Not in any conventional sense.
~Especially since a static class is completely different from a class with all static methods.

Difference between custom controller and interface component

Hi,
Can anybody tell me what are the differences between component controller and custome controller , component interface.
Thanks in advance.
Regards
sireesha.

hi,
When any component is created web dynpro framework automatically generates the controller(controller is nothing but entity which controls the working of views and acts as a binding layer between model and view), this controller is called Component controller.
We can have as many controller as we want, but they should be used sparingly, Controller should encapsulate the functionality which is common to whole component , like if your application fetches master data and appliaction data so better you should have 2 controller , 1 for master and 2 for application so as to have modularisation in your application.
Component Interface is the entity which is used when you want to use the functionality defined in some other component i.e. if your main component is acting as a parent comopnent then the child component usage should be defined via this interface controller under Component Interface, so that main compo will access it via childs Interface Controller.
Other node under this , Interface view , gets generated for every creation of window , Interface view is entry point into our application for web Dynpro framework
jsut check out following links,
Re: Difference between Component Controller and Custom Controllet...?
Re: custom vs component controller
check out these ex for the Component Interface and node under this,
https://www.sdn.sap.com/irj/sdn/downloaditem?rid=/webcontent/uuid/19e6e990-0201-0010-eca6-a62e342eaad3 [original link is broken]
https://www.sdn.sap.com/irj/sdn/downloaditem?rid=/webcontent/uuid/1208c2cd-0401-0010-4ab6-f4736074acc6 [original link is broken]
https://www.sdn.sap.com/irj/sdn/downloaditem?rid=/webcontent/uuid/1ee0e990-0201-0010-75bf-a087c241cb83 [original link is broken]
hope it helps
regards

Difference between abstact class and interface

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