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how to compare two user defined objects in java?

Posted on 2011-03-08
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Last Modified: 2012-05-11
Hi,

Please explain, how to compare two user defined objects in java, Kindly explain this with an example, because i have reffered so many articles, but still confusing.

Please do need full.

Thanks....
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Question by:haneef_nb
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6 Comments
 
LVL 86

Expert Comment

by:CEHJ
ID: 35069735
You use either a Comparator or make the object implement Comparable

http://lkamal.blogspot.com/2008/07/java-sorting-comparator-vs-comparable.html
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Author Comment

by:haneef_nb
ID: 35069739
suppose we have Employee object, if the empId is same, then we should not allow that object to add in collection....
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LVL 86

Expert Comment

by:CEHJ
ID: 35069754
Yes. All you'd need for that is to use a Set. Return the empId as the value of hashCode and implements Employee.equals based on empId. Simple
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LVL 20

Accepted Solution

by:
a_b earned 2000 total points
ID: 35069758
You will have to override the equals() method.

Eg.
class Student
{
    pvt string firstName;
    pvt string lastName;
    pvt string addressName;


   public boolean equals(Object o)
   {
        if(o instance of Student)
        {
                Student s = (Student) o;
                if(firstName.equals(s.firstName) && lastName.equals(s.lastName) && addressName.equals(s.addressName))
                        return true;
      }
return false;

   }

}

I've missed out the getters and setters
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LVL 92

Expert Comment

by:objects
ID: 35074856
> if the empId is same, then we should not allow that object to add in collection....

you need to first check if the object is in the collection.
The actual comparison is done with the equals() method which you need to overrride as a_b has shown above. In that method you define when two objects are considered to be equal
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Author Closing Comment

by:haneef_nb
ID: 35206972
Thanks..
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