Overriding and Overloading

Overriding #

• Redefining a method of an inherited class.
• For method overriding, the return type, method name, number of parameters, and data types of parameters must all be identical.

public class OverridingEx{
static int sum = 0;

class A {
  public void add(){
    sum = sum + 1;
  }
}
class B extends A {
  // Overriding
  public void add(){
    sum = sum + 15;
  }
}

public static void main(String[] args){
    A a = new A();
    B b = new B();

    a.add();
    System.out.println(sum); // 1
    b.add();
   System.out.println(sum); // 11
  }
}

• If you change the object instance creation code here to A a = new B();, the add method in class B will be called. That is,
• In inheritance, when a superclass and a subclass have methods with the same name, the method that is called is determined by the instance.

The technique by which an instance's method is called is known as virtual method.

Overloading #

• It is the definition of methods that use the same name but differ in the number of parameters, their data types, or their return types.
• Overloading is often seen when creating constructors.

public cass name{
  String firstName;
  String middleName;
  String lastName;

  public name (String fn){
    this.firstName = fn;
  }

  public name (String fn, STring ln){
    this.firstName = fn;
    this.lastName = ln;
  }
  public name (String fn, String mn, String ln){
    this.firstName = fn;
    this.middleName = mn;
    this.lastName = ln;
  }
}

• All constructors have the same name, name, but differ in the number of parameters.
• When a user calls the name method, the Java compiler searches for a name method that has the same parameter types, the same number of parameters, and the same return type as the one called.