Collections.reverseOrder() in Java with Examples
java.util.Collections.reverseOrder() method is a java.util.Collections class method.
// Returns a comparator that imposes the reverse of // the natural ordering on a collection of objects // that implement the Comparable interface. // The natural ordering is the ordering imposed by // the objects' own compareTo method public static Comparator reverseOrder()
We can the comparator returned by Collections.reverseOrder() to sort a list in descending order.
List after the use of Collection.reverseOrder() and Collections.sort(): [50, 40, 30, 20, 10]
We can use this method with Arrays.sort() also.
Arrays.sort() cannot be used directly to sort primitive arrays in descending order. If you try to call the Arrays.sort() method by passing reverse Comparator defined by Collections.reverseOrder() , it will throw the error.
That will work fine with ‘Array of Objects’ such as the Integer array but will not work with a primitive array such as the int array.
Array after the use of Collection.reverseOrder() and Arrays.sort() : [40, 30, 20, 10]
public static Comparator reverseOrder(Comparator c)
It returns a Comparator that imposes reverse order of a passed Comparator object. We can use this method to sort a list in reverse order of user defined Comparator. For example, in the below program, we have created a reverse of user defined comparator to sort students in descending order of roll numbers.
Unsorted 111 bbbb london 131 aaaa nyc 121 cccc jaipur Sorted by rollno 131 aaaa nyc 121 cccc jaipur 111 bbbb london
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