Java Abstract Methods [duplicate]

Question

I am slightly confused with the keyword abstract here. My compiler is telling me that I am not allowed to have a body for a method that's abstract. However my assignment says:

The abstract method orderDescription() returns a String giving details about a particular order.

abstract String orderDescription()
{
    return null;
}

However my code returns an error, as I mentioned above. So my question is what should I do for this problem?

Up to now I've just removed the keyword abstract and it works fine.

Answer 1

abstract String orderDescription()
{
    return null;
}

should be

abstract String orderDescription();

As error says, your abstract method declaration shouldn't contain any body.

Above syntax mandates the implementation (which ever class extends the abstract class and provides implementation) to return a String.

You can't instantiate abstract class, so some class need to extend abstract class and provide implementation for this abstract method.

Example:

class MyabsClass 
{
  abstract String orderDescription();
}

class MyImplementation extends MyabsClass
{
   public String orderDescription()
    {
    return "This is description";
    }
}



 class MyClient
   {
     public static void main(String[] args)
      {
         MyImplementation imple = new MyImplementation();
         imple.orderDescription();
      }
   } 

Answer 2

When you define an abstract method, you are telling the compiler that any subclasses must provide an implementation (or also declare themselves abstract).

You implement the abstract method in a subclass.

Remember, you cannot create instances of abstract classes themselves. The entire point of an abstract method is to tell the compiler that you want subclasses to provide the functionality.

Answer 3

Essentially, an abstract function shouldn't contain any details, it is a placeholder function for inherited functions. As Nambari stated, you should only include the definition.

This is used for when you want a family of classes to all contain a common function, which you wish each child class to define.