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Which is best to use in hashcode?

 
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Hello Everyone,
which is best scenario for hashcode?
A> Use two instance variable to calculate the hashcode.
B> Use only one instance variable to calculate the hashcode.

If in exam i get both the option with complex code which option should i choose?? According to me A should be appropriate. What do you think??
 
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A good hashCode implementation returns unique hash codes for different objects. So the following is a very inefficient implementation of hashCode method
 
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If this question qualifies to be appeared in exams as it is given here , then my answer will also be A.

 
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This question is impossible to answer, because whatever is "best" depends on the meaning of the class for which you are implementing the hashCode() method and also on what "equality" means for objects of that class. You will not get vague questions like this on the exam.
 
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Hi, How to write good hashCode() implementation..Here is a small program
 
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Actually Saibabaa, while your equals method isn't necessarily wrong, it's better to compare using equals. I made some changed to your example, feel free to ask my why I made some of the changes:
 
Saibabaa Pragada
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Hi Stephan, I changed your code with 3 comments/questions. Could you please advice ?
 
Stephan van Hulst
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1) In general it's a good idea not to allow null values unless they have a special meaning. In this case, it doesn't make sense for a dog not to have a name, so we don't allow null. It's best to throw exceptions as soon as possible, so in this case we throw NullPointerException in the constructor. Now we don't have to worry in other methods that name could be null, so we don't have to check every time we use name.

2) Your version of the equals method was good, except for using == instead of equals. I'm just used to writing it this way. The only real difference is that I check first whether o == this. The method should work fine without it, but this is a small optimization, so the method returns quickly if the object is being compared to itself.

3) Yes, you are correct. Here is a small example that shows how you should implement hashCode and equals methods for a class that holds different kinds of member fields:
 
Saibabaa Pragada
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Nice..Thank you Stephan
 
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Great work Stephan van Hulst.
 
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