Inquisition Mock - Doubt

[Shivani Sharma]

Hi Guys

In the following code :

    
class Test
{
   int x; Test(int input) { x = input; }
   public static void main( String args[] )
   {
      System.out.println( new Test(3).equals(new Test(3)) );
   }
   public boolean equals( Object o)
   {
      return ( (Test)o ).x == x;
   }
}

Ans given is true.

Shouldn't it be false as hashcode is not overidden.

[Sebastian Janisch]

No ... hashCode becomes important when working with collections to determine lookup locations for objects.

In collections, the hashCode determines the location to look for the object, then equals determines equality. Which also means two identical hashCode do not necessarily mean equality. The opposite however is true. Two equal objects must have the same hashCode.

[Harsh Pensi]

Hi Shivani
I failed to understand why you need hashcode here
hashcode method has to be overridden if you want to be able to use the class properly in a collection that uses hashing.

[Deepak Bala]

Shivani Sharma wrote:Hi Guys

In the following code :

    
class Test
{
   int x; Test(int input) { x = input; }
   public static void main( String args[] )
   {
      System.out.println( new Test(3).equals(new Test(3)) );
   }
   public boolean equals( Object o)
   {
      return ( (Test)o ).x == x;
   }
}

Ans given is true.

Shouldn't it be false as hashcode is not overidden.

There is no underlying structure that tries to put these objects into "buckets". Try this

  
Set<Test> set = new HashSet<Test>();
set.add(new Test(3));
set.add(new Test(3));
System.out.println(set.size());
  

[Shivani Sharma]

Thanks a lot guys, got it.