Overloading

[Murtuza Akhtari]

Check the following codes

class A {void m1(A a) {System.out.print("A");}}
class B extends A {void m1(B b) {System.out.print("B");}}
class C extends B {void m1(C c) {System.out.print("C");}}
class D {
  public static void main(String[] args) {
    A c1 = new C(); B c2 = new C(); C c3 = new C(); C c4 = new C();
    c4.m1(c1); c4.m1(c2); c4.m1(c3);
}}
 
What is the result of attempting to compile and run the program? 
 
a.  Prints: AAA 
b.  Prints: ABC 
c.  Prints: CCC 
d.  Compile-time error 
e.  Run-time error 
f.  None of the above 

Answer:b. explanation for this answer is that the reference variable is NOT used for selection but the reference Argument is used.

class A {void m1(A a) {System.out.print("A");}}
class B extends A {void m1(B b) {System.out.print("B");}}
class C extends B {void m1(C c) {System.out.print("C");}}
class D {
  public static void main(String[] args) {
    A c1 = new C(); C c2 = new C(); c1.m1(c2);
}}
 
What is the result of attempting to compile and run the program? 
 
a.  Prints: A 
b.  Prints: B 
c.  Prints: C 
d.  Compile-time error 
e.  Run-time error 
f.  None of the above 

Answer: a.Explanation for this answer is that the reference variable c1 is used to determine which m1() will be called. Since c1 is of type A therefore A's m1() is called.

My question is why does it check the reference argument in the first case and the reference variable in the second. What am i missing ??

[Kitty Dayal]

Hi Murtuza,

class A {void m1(A a) {System.out.print("A");}}
class B extends A {void m1(B b) {System.out.print("B");}}
class C extends B {void m1(C c) {System.out.print("C");}}
class D {
  public static void main(String[] args) {
    A c1 = new C(); B c2 = new C(); C c3 = new C(); C c4 = new C();
    c4.m1(c1); c4.m1(c2); c4.m1(c3);
}}
 
What is the result of attempting to compile and run the program? 
 
a.  Prints: AAA 
b.  Prints: ABC 
c.  Prints: CCC 
d.  Compile-time error 
e.  Run-time error 
f.  None of the above 

Overloaded methods go by reference type at run-time.

In this case the methods are overloaded. when c4.m1(c1) is executed it goes to m1() method of class C(ref type), but since the arguments does not match it goes to immediate superclass(since its overloaded) and checks whether it match's and so on. When it matchs class A's m1() method it prints A. Similarly B. For c4.m1(c3) it matchs exactly so C. so the answer ABC.

class A {void m1(A a) {System.out.print("A");}}
class B extends A {void m1(B b) {System.out.print("B");}}
class C extends B {void m1(C c) {System.out.print("C");}}
class D {
  public static void main(String[] args) {
    A c1 = new C(); C c2 = new C(); c1.m1(c2);
}}
 
What is the result of attempting to compile and run the program? 
 
a.  Prints: A 
b.  Prints: B 
c.  Prints: C 
d.  Compile-time error 
e.  Run-time error 
f.  None of the above 

[\QUOTE]

As said before overloaded goes by reference type. So the statement
A c1 = new C(); //
Here the ref. type is A and so goes directly into class A and executes m1() and prints A. Also note here that the subclass argument(c2) is casted implicitly to superclass type.

Hope that clears your doubt.
Kits

[Murtuza Akhtari]

Thanks Kitty....
that was helpful !!

[Dan Chisholm]

Here's a sample chapter from my book that covers method overloading.