Java overload override inheritance polymorphism

Apr 25, 2012

Java overload, override, inheritance, and polymorphism.

overload

• Multiple methods with the same name but different in:
  • parameters number;
  • or
  • parameters type;
• Excluding the following cases:
  • different parameters name;
  • different return type;

override

• Subclass declares methods that are already present in its parent class:
  • with argument list (type and sequence) the same as that of the parent;
  • with return type the same or subtype of that of the parent;
  • with narrower or fewer checked exceptions than that of the parent;
  • and access modifier not being more restrictive than that of the parent;
• Except for the following cases:
  • method declared ‘final’ cannot be overridden;
  • method declared ‘static’ cannot be overridden;
  • method declared ‘private’ cannot be inherited therefore not overridden;
  • constructors cannot be overridden;

inheritance

• The extends keyword is used for inheritance;
• Child class derives from parent class with all nonstatic/nonprivate members;

polymorphism

• Child inherits and overrides parent method;
• Parent variable references child and the behavior is based on child method;

example

class Triangle extends Shape
{
      // method overriding
      public int getSides()
      {
        return 3;
      }
}

class Rectangle extends Shape
{
      public int getSides(int i)
      {
        return i;
      }
}

public class Shape
{
      public boolean isShape()
      {
        return true;
      }

      public int getSides()
      {
        return 0;
      }

      // method overloading      
      public int getSides(Triangle tri)
      {
        return 3;
      }

      public int getSides(Rectangle rec)
      {
        return 4;
      }

      public static void main(String[] args)
      {
            Triangle triangle = new Triangle();
            System.out.println(triangle.isShape()); // inheritance

            Shape shape = new Triangle();
            System.out.println(shape.getSides());  // polymorphism
      }
}

java