CODEWITHSUNDEEP
javaclasssortingcollections
Ashish Negi
Ashish Negi

Reputation: 5301

Collections.sort in java for any class

Java class problem

In C++ if we add some class objects to vector , we can sort the list by specifying some functions like operator<() or operator==() or operator!=.

What do we need to do in java for Collections.sort to work according to our wishes

Upvotes: 2

Views: 1540

Answers (5)

bstick12
bstick12

Reputation: 1749

You can either implement Comparable or you can pass a Comparator to Collections.sort

Upvotes: 1

Richard H
Richard H

Reputation: 39055

You need to write a Comparator - typically you just override the compare method which returns an int, +ve, 0 or -ve to indicate "greater than", "the same" or "less than" for whatever definitions of these you choose. See another of my answers for an example.

Upvotes: 2

Dirk
Dirk

Reputation: 1903

Your class needs to implement the Comparable interface in order for sort to work.

Upvotes: 3

Jon Skeet
Jon Skeet

Reputation: 1499900

You implement Comparable<T>.

From the docs for Collections.sort:

Sorts the specified list into ascending order, according to the natural ordering of its elements. All elements in the list must implement the Comparable interface. Furthermore, all elements in the list must be mutually comparable (that is, e1.compareTo(e2) must not throw a ClassCastException for any elements e1 and e2 in the list).

Alternatively, if you don't control the element type (e.g. you've got a List<String> and you want to apply a custom sort order) you implement Comparator<T> and pass that in as an extra parameter to Collections.sort

Upvotes: 8

b.buchhold
b.buchhold

Reputation: 3896

Let your class implement the Comparable interface

Upvotes: 2

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