abstract data type

[Jenny raj]

anyone please explain what is an abstract data types in java?
thanks

[Shyam Prasad Murarka]

Dear Reader,
This keyword is used wwhile declaring classes and methods.
For eg.

public abstract class MyAbstractClass
{
    //code
    public abstract void method();    
}

When used with a class, it does NOT allow any instantiations of it. It means you will not be able to create any object for the above class "MyAbstractClass". This is used when you are not sure about the implementation of the class and the class only gets its real meaning when its extended by some other class.

Absract methods are not given any body. They are only declared.
Note: I have used a semicolon after the method signature.

The body for the method is defined by any class that extends its class.

Here's an example:

public abstract class Animal
{
    abstract void walk();    
}
 
public class Dog extends Animal
{
    void walk()
    {
         //Implementation is done here
    }
}

You really don't know what an Animal object looks like. Does it have four legs or four horns. There is no definite meaning for it. So you NEED to subclass it to give it a proper shape such as a Dog.
Different Animals have different styles of walking, so we just declare an abstract method for walk() and leave it to the sub-classes to implement a specific style for its class.

Now, there are many rules associated with the "abstract" keyword which you can learn once you understand this concept.

[Ernest Friedman-Hill]

Although the above is a good explanation of the "abstract" keyword in Java, it actually doesn't answer the question at all.

"Abstract data type" -- often abbreviated ADT -- is basically an old-fashioned term for "class". If you know what a Java class is -- especially if you understand it as some data plus some operations on that data -- then you understand what an ADT is.

[Shyam Prasad Murarka]

Dear Reader,
When I read "abstract data type" I though Jenny must have made a typo. I never knew any term such as "ADT" even existed! But thanks to Ernest, I am now aware of it.

[Jenny raj]

Hi shyam

I know the concept of abstract
but as my other friend said i wanted to know what ADT is all about?

like where do we apply in java.

still i am not clear..

any suggestion would be appreciated

thanks

[Shyam Prasad Murarka]

Dear Reader,
Have you read Ernest's post properly. Everything about ADT is there! Like he told, its just an old-fashioned term for 'class'. I don't know if there's anything more to that.

[Jeff Albertson]

You may want to read the Wikipedia article: http://en.wikipedia.org/wiki/Abstract_data_type