Regarding polymorphism

Question

Hi
I have doubt regarding polymorphism.Why we are calling oveloading is
compiletime polymorphism and overridding is called runtime polymorphism.

Answer 1

satishnarayan wrote:
Hi
I have doubt regarding polymorphism.Why we are calling oveloading is
compiletime polymorphism and overridding is called runtime polymorphism.Because with overloading, the compiler knows exactly which method signature will be called, but with overriding, it's the JVM--the runtime environment--that discovers which class' version of the method will be called.
public class Parent {
  // overloading
  public void foo(Object obj) { System.out.println("obj"); }
  public void foo(String str) { System.out.println("str"); }
  // overriding
  public void bar() { System.out.println("parent"); }
public class Child extends Parent {
  public void bar() { System.out.println("child"); }
Object obj1 = new Object(); // compiler only knows obj1 Object reference, not new Object()
Object obj2 = "abc"; // compiler only knows obj2 Object reference, not that the object it points to at runtime will be a String
String str = "xyz"; // compiler only knows String reference type for str variable
Parent p1 = new Parent();
p1.foo(obj1); // "obj"
p1.foo(obj2); // "obj"
p1.foo(str); // "str"
Parent p2 = new Child();
Child c = new Child();
p1.bar(); // "Parent"
p2.bar(); // "Child"
c.bar(); // "Child"The compiler knows the type of the reference, but it doesn't know the class of the object that reference will point to at runtime. p2 = new Child(); could have been replaced with a method that randomly returns a Parent, a Child, or any other subclass of Parent. Whose version of the bar() method gets called is determined by what that runtime object is.
With overloading, it doesn't matter what the runtime class of the object is. Which signature gets called is entirely determined by the compile-time types of the parameter references.