Only 44 hours left in the trailboss' kickstarter!

New rewards and stretch goals. CLICK HERE!



Win a copy of Murach's Python Programming this week in the Jython/Python forum!
  • Post Reply Bookmark Topic Watch Topic
  • New Topic

Confused in equals working and its overriding  RSS feed

 
Devendra Walanj
Greenhorn
Posts: 12
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
Hello,
by following code :


the result why a.equals(a1) is false ?
Please explain how equal and instanceof works with classes and objects.
How does equals work at the low level?
Pretty confused in the area.
 
Radovan Vukovic
Greenhorn
Posts: 19
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
have you check hashCode()
hashCode must generate equal values for equal objects
 
Paul Clapham
Sheriff
Posts: 22185
38
Eclipse IDE Firefox Browser MySQL Database
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
How does equals work at the low level?

I take this to mean "If I don't override the equals(Object) method from the Object class then how does equals() work for my class?"

In that case the equals() method from Object is used. And that method returns true if the two objects being compared are the same object, and false if they are different objects.

In your example you are comparing two different objects, so the equals() method returns false.

And no, declaring a hashCode method has no effect on the result of equals().
 
Mohamed Sanaulla
Bartender
Posts: 3169
34
Google App Engine Java Ruby
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
Just to add to what Paul said.

References here mean the variable names. And Instances mean the actual object created with the "new" command.
The default implementation of equals() method (provided in the class Object)- checks if the 2 References are pointing to the same object on the heap.


You see that the default implementation doesnt actually check the contents of the objects these references point to, instead it just checks if these references point to the same object.

You can override the equals() method in your class and then provide a check to see if the contents are also equal.
 
santosh dhulipala
Ranch Hand
Posts: 52
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
my doubt is
for comparison of two String's equal method check the contents
will it compare form the hascode genrated
as when creating strings it will verify if it already exist in the String pool if not create the new one and store the address





 
Campbell Ritchie
Sheriff
Posts: 53720
127
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
That applies to Strings and the wrapper classes (to a limited extent), but doesn't apply to your classes.

And I don't believe the String#equals(java.lang.Object) method uses the hash code. You would have to look in src.zip to be sure.
 
With a little knowledge, a cast iron skillet is non-stick and lasts a lifetime.
  • Post Reply Bookmark Topic Watch Topic
  • New Topic
Boost this thread!