Reverse a comparator in Java 8

Question

I have an ArrayList and want sort it in descending order  I use for it java util stream Stream sorted Comparator  method  Here is a description according Java API      Returns a stream consisting of the elements of this stream  sorted according to the provided Comparator    this methods return me a sort with ascending order  Which parameter should I change  just to have the descending order

User · Answer

Why not to extend the existing comperator and overwrite super and nor the result. The implementation the Comperator Interface is not nessesery but it makes it more clear what happens.

In result you get a easy reusable Class File, testable unit step and clear javadoc.

public class NorCoperator extends ExistingComperator implements Comparator<MyClass> {
    @Override
    public int compare(MyClass a, MyClass b) throws Exception {
        return super.compare(a, b)*-1;
    }
}

User · Answer

You can also use Comparator comparing Function  Comparator  It is convenient to chain comparators when necessary  e g    Comparator lt SomeEntity gt  ENTITY COMPARATOR   comparing SomeEntity  getProperty1  reverseOrder             thenComparingInt SomeEntity  getProperty2           thenComparing SomeEntity  getProperty3  reverseOrder

User · Answer

Java 8 Comparator interface has a reversed method   https   docs oracle com javase 8 docs api java util Comparator html reversed--

User · Answer

You can use Comparator reverseOrder   to have a comparator giving the reverse of the natural ordering   If you want to reverse the ordering of an existing comparator  you can use Comparator reversed     Sample code   Stream of 1  4  2  5       sorted Comparator reverseOrder             stream is now  5  4  2  1   Stream of  foo    test    a        sorted Comparator comparingInt String  length  reversed             stream is now  test  foo  a   sorted by descending length

[java] Reverse a comparator in Java 8

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