Need help on overridding

Question

I have listed couple of my questions on overridding here.
class ParentClass{
     void method1(Object b){
     System.err.println("in object");     
     void method1(Double d){
          System.err.println("in double");
public class ChildClass extends ParentClass{
     public static void main(String args[]){
          ChildClass c = new ChildClass();
          c.method1(null);  // *Question 1*      
                       c.method1(3);    // *Question 2*     
Question 1 - Will print "in Double" ? Why not it prints "in Object" ?
Question 2 - Will print "in Object" its an int value how it prints object?

Answer 1

Questions 2 and 3 are due to auto-boxing. When you try to assign a primitive to a reference type (which is what is happening when you include it as an argument to a method that takes an Object, etc), the primitive is "auto-boxed" to its primitive wrapper class, in this case, int to Integer. Since Integer is not a double, Question 2 links to method1(Object) as that is the only candidate. Likewise, in Question 3, method1(Integer) is the most specific matching signature, so it is chosen.
Question 1 actually surprised me. I thought it would be ambiguous, but I guess because there is a clear hierarchy to Double and Object (Double indirectly extends Object), there is no ambiguity. The most specific method is chosen.
Note that if you had method1(String) and method1(Double), Question 1 would be a compile error since it would be ambiguous (String is not an ancestor of Double, and vice versa, so there is no way to tell which you mean.) Whenever you pass null as an argument, you can cast it to be explicit:
c.method1((Object)null);And yes, in the future, please be more careful with which forum you choose to post in.