Inheritance

Once a class is defined, it may be used as a model for another class by using the C++ syntax class Child : public Parent or Java syntax class Child extends Parent. The new Child class inherits all of the attributes, and methods of the Parent class. Additional attributes and methods may then be added to the Childclass, without effecting the Parent class. The Childclass is derived from the Parent.

Here is an easy to understand example, using three classes.


// C++ implementation
  class Grandpa            class Mom               class Dad : public Grandpa
  {                        {                       {
    protected:               protected:              protected:
      int big_ears;            float eyes;             char mouth;
      .                        .                       .
      .                        .                       .    
                      
  }                        }                       }                    

// Java implementation
public class Grandpa   	   public class Mom        public class Dad extends Grandpa
{                          {                       {
  protected int big_ears;    protected float eyes;   protected char mouth;
  ....                       ....                    ....
}                          }                       }

Notice that Dad is derived from Grandpa . We will now declare one more class that will bring these together.

// C++ allows multiple inheritance
class Me : public Mom, public Dad
{
   private:
     unsigned int freckles;
}

The class me will end up with Mom's eyes, Dad's mouth, and Grandpa's big_ears, since Dad was derived from Grandpa. In this example, freckles is an attribute that only exists in the class me.

// Java doesn't support multiple inheritance
public class Me extends Dad
{ // notice that class Me inherits from Dad ONLY
  private int freckles;
  private float eyes; // not from Mom
  ...
}

This example only dealt with data, however the situation would occur with any methods (functions) that were contained in the base classes. Question: Why PROTECTED is used ?

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