28. Abstract Classes

• Presence of a single abstract method makes a class abstract.

• It is prohibited to create objects of abstract classes.

• It is allowed to create variables of a reference or pointer to an abstract class type.

• Abstract classes can have data members and non-abstract methods.

• Abstract method and class in Java:

  
      public abstract class Document
      {
          public abstract void print();
          //...
  
      }//abstract class Document