Regarding Comparator and Comparable interfaces

[Mansukhdeep Thind]

Hi all

I went through the material in SCJP Exam Study Guide but couldn't quite understand the concept behind java.util.Comparator and java.lang.Comparable interfaces and how and when to use these. Can anyone please provide some material / simple code examples which shed some light on these topics for a beginner?

Regards
Mansukhdeep

[Vinoth Kumar Kannan]

tried google? that might help..

[Paul Clapham]

Suitable Google keywords for your question would be "java comparator comparable".

[Shanky Sohar]

java.lang.Comparable: int compareTo(Object o1)
This method compares this object with o1 object. Returned int value has the following meanings.
positive – this object is greater than o1
zero – this object equals to o1
negative – this object is less than o1

java.lang.Comparator: int compare(Object o1, Objecto2)
This method compares o1 and o2 objects. Returned int value has the following meanings.
positive – o1 is greater than o2
zero – o1 equals to o2
negative – o1 is less than o1



we can have only one implementation of compareTo() or Compare() method in one class

[Virendrasinh Gohil]

shanky sohar wrote:we can have only one implementation of compareTo() or Compare() method in one class

Shanky, just to correct you. There is no compiler restriction to have both the methods in single class. A class can very well implement both the interfaces at the same time and can implement both the methods without conflict. I think you actually meant, there is no use of implementing compareTo() and compare() methods (and Comparable & Comparator interfaces) in a single class. Both the method serves same purpose but differs the way both are used.

[Campbell Ritchie]

You would find this and this and doubtless lots more if you would search JavaRanch.

[Shanky Sohar]

Virendrasinh Gohil wrote:

shanky sohar wrote:we can have only one implementation of compareTo() or Compare() method in one class

Shanky, just to correct you. There is no compiler restriction to have both the methods in single class. A class can very well implement both the interfaces at the same time and can implement both the methods without conflict. I think you actually meant, there is no use of implementing compareTo() and compare() methods (and Comparable & Comparator interfaces) in a single class. Both the method serves same purpose but differs the way both are used.

I mean to say we can not have implementation of compareTo() twice in a single class
and same is for campare()