Java Array Sort descending

Question

Is there any EASY way to sort an array in descending order like how they have a sort in ascending order in the Arrays class   Or do I have to stop being lazy and do this myself

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without explicit comparator   Collections sort list  Collections reverseOrder       with explicit comparator    Collections sort list  Collections reverseOrder new Comparator

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Another way with Comparator  import java util Arrays  import java util Comparator       Integer   aInt    6 2 3 4 1 5 7 8 9 10   Arrays sort aInt  Comparator reverseOrder

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I had the below working solution     public static int   sortArrayDesc int   intArray       Arrays sort intArray                          sort intArray in Asc order     int   sortedArray   new int intArray length       this array will hold the sorted values      int indexSortedArray   0      for int i intArray length-1   i  gt   0   i--        insert to sortedArray in reverse order         sortedArray indexSortedArray       intArray  i             return sortedArray

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Another solution is that if you re making use of the Comparable interface you can switch the output values which you had specified in your compareTo Object bCompared    For Example    public int compareTo freq arg0         int ret 0      if this magnitude gt arg0 magnitude          ret  1      else if  this magnitude  arg0 magnitude          ret  0      else if  this magnitude lt arg0 magnitude          ret  -1      return ret      Where magnitude is an attribute with datatype double in my program  This was sorting my defined class freq in reverse order by it s magnitude  So in order to correct that  you switch the values returned by the  lt  and  gt   This gives you the following     public int compareTo freq arg0         int ret 0      if this magnitude gt arg0 magnitude          ret  -1      else if  this magnitude  arg0 magnitude          ret  0      else if  this magnitude lt arg0 magnitude          ret  1      return ret      To make use of this compareTo  we simply call Arrays sort mFreq  which will give you the sorted array freq    mFreq   The beauty  in my opinion  of this solution is that it can be used to sort user defined classes  and even more than that sort them by a specific attribute  If implementation of a Comparable interface sounds daunting to you  I d encourage you not to think that way  it actually isn t  This link on how to implement comparable made things much easier for me  Hoping persons can make use of this solution  and that your joy will even be comparable to mine

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It s not directly possible to reverse sort an array of primitives  i e   int   arr    1  2  3    using Arrays sort   and Collections reverseOrder   because those methods require reference types  Integer  instead of primitive types  int    However  we can use Java 8 Stream to first box the array to sort in reverse order      an array of ints int   arr    1  2  3  4  5  6       an array of reverse sorted ints int   arrDesc   Arrays stream arr  boxed        sorted Collections reverseOrder         mapToInt Integer  intValue       toArray     System out println Arrays toString arrDesc       outputs  6  5  4  3  2  1

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First you need to sort your array using  Collections sort myArray    Then you need to reverse the order from ascending to descending using  Collections reverse myArray

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You could use this to sort all kind of Objects  sort T   a  Comparator lt   super T gt  c    Arrays sort a  Collections reverseOrder       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      no suitable method found for sort int   comparator    That will work fine with  Array of Objects  such as Integer array but will not work with a primitive array such as int array   The only way to sort a primitive array in descending order is  first sort the array in ascending order and then reverse the array in place  This is also true for two-dimensional primitive arrays

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There is a lot of mess going on here - people suggest solutions for non-primitive values  try to implement some sorting algos from the ground  give solutions involving additional libraries  showing off some hacky ones etc  The answer to the original question is 50 50  For those who just want to copy paste      our initial int   array containing primitives int   arrOfPrimitives   new int   1 2 3 4 5 6       we have to convert it into array of Objects  using java s boxing Integer   arrOfObjects   new Integer arrOfPrimitives length   for  int i   0  i  lt  arrOfPrimitives length  i         arrOfObjects i    new Integer arrOfPrimitives i        now when we have an array of Objects we can use that nice built-in method Arrays sort arrOfObjects  Collections reverseOrder       arrOfObjects is  6 5 4 3 2 1  now  If you have an array of something other than ints - use the corresponding object instead of Integer

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When an array is a type of Integer class then you can use below  Integer   arr    7  10  4  3  20  15   Arrays sort arr  Collections reverseOrder      When an array is a type of int data type then you can use below  int   arr    7  10  4  3  20  15   int   reverseArr   IntStream rangeClosed 1  arr length  map i - gt  arr arr length-i   toArray

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You could use stream operations  Collections stream    with Comparator reverseOrder     For example  say you have this collection   List lt String gt  items   new ArrayList lt  gt     items add  item01    items add  item02    items add  item03    items add  item04    items add  item04      To print the items in their  natural  order you could use the sorted   method  or leave it out and get the same result    items stream         sorted         forEach item - gt  System out println item      Or to print them in descending  reverse  order  you could use the sorted method that takes a Comparator and reverse the order   items stream         sorted Comparator reverseOrder          forEach item - gt  System out println item      Note this requires the collection to have implemented Comparable  as do Integer  String  etc

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I don t know what your use case was  however in addition to other answers here another  lazy  option is to still sort in ascending order as you indicate but then iterate in reverse order instead

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I know that this is a quite old thread  but here is an updated version for Integers and Java 8   Arrays sort array   o1  o2  - gt  o2 - o1     Note that it is  o1 - o2  for the normal ascending order  or Comparator comparingInt      This also works for any other kinds of Objects  Say   Arrays sort array   o1  o2  - gt  o2 getValue   - o1 getValue

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for a list  Collections sort list  Collections reverseOrder       for an array  Arrays sort array  Collections reverseOrder

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For discussions above  here is an easy example to sort the primitive arrays in descending order   import java util Arrays   public class Main       public static void main String   args            int   nums     5  4  1  2  9  7  3  8  6  0            Arrays sort nums               reverse the array  just like dumping the array             swap 1st  1st-last   lt   1st  0  1st-last  nums length - 1            swap 2nd  2nd-last   lt   2nd  i     2nd-last  j--            swap 3rd  3rd-last   lt   3rd  i     3rd-last  j--                    for  int i   0  j   nums length - 1  tmp  i  lt  j  i    j--                tmp   nums i               nums i    nums j               nums j    tmp                        dump the array  for Java 4 5 6 7 8 9          for  int i   0  i  lt  nums length  i                  System out println  nums     i            nums i                        Output   nums 0    9 nums 1    8 nums 2    7 nums 3    6 nums 4    5 nums 5    4 nums 6    3 nums 7    2 nums 8    1 nums 9    0

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There is a way that might be a little bit longer  but it works fine  This is a method to sort an int array descendingly  Hope that this will help someone     some day  public static int   sortArray  int   array        int    sortedArray   new int array length       for  int i   0  i  lt  sortedArray length  i              sortedArray i    array i                  boolean flag   true      int temp      while  flag            flag   false          for  int i   0  i  lt  sortedArray length - 1  i                  if sortedArray i   lt  sortedArray i 1                     temp   sortedArray i                   sortedArray i    sortedArray i 1                   sortedArray i 1    temp                  flag   true                                         return sortedArray

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It s good sometimes we practice over an example  here is a full one  sortdesc java import java util Arrays  import java util Collections  class sortdesc  public static void main String   args             int Array        Integer   intArray new Integer                     new Integer 15                    new Integer 9                    new Integer 16                    new Integer 2                    new Integer 30               Sorting int Array in descending order        Arrays sort intArray Collections reverseOrder                Displaying elements of int Array        System out println  quot Int Array Elements in reverse order  quot           for int i 0 i lt intArray length i              System out println intArray i               String Array        String   stringArray new String    quot FF quot   quot PP quot   quot AA quot   quot OO quot   quot DD quot               Sorting String Array in descending order        Arrays sort stringArray Collections reverseOrder                Displaying elements of String Array        System out println  quot String Array Elements in reverse order  quot           for int i 0 i lt stringArray length i              System out println stringArray i       compiling it    javac sortdec java  calling it    java sortdesc  OUTPUT Int Array Elements in reverse order  30 16 15 9 2 String Array Elements in reverse order  PP OO FF DD AA  If you want to try an alphanumeric array      replace this line  String   stringArray new String    quot FF quot   quot PP quot   quot AA quot   quot OO quot   quot DD quot       with this  String   stringArray new String    quot 10FF quot   quot 20AA quot   quot 50AA quot     you gonna get the OUTPUT as follow  50AA 20AA 10FF  source

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You can use this       Arrays sort data  Collections reverseOrder       Collections reverseOrder   returns a Comparator using the inverse natural order  You can get an inverted version of your own comparator using Collections reverseOrder myComparator

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an alternative could be  for numbers        multiply the Array by -1 sort multiply once again with -1   Literally spoken   array   -Arrays sort -array

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Simple method to sort an int array descending   private static int   descendingArray int   array        Arrays sort array       int   descArray   new int array length       for int i 0  i lt array length  i              descArray i    array  array length-1 -i             return descArray

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This worked for me   package doublearraysort   import java util Arrays  import java util Collections   public class Gpa         public static void main String   args               initializing unsorted double array         Double   dArr   new Double                                  new Double 3 2               new Double 1 2               new Double 4 7               new Double 3 3               new Double 4 6                            print all the elements available in list         for  double number   dArr                System out println  GPA       number                         sorting the array         Arrays sort dArr  Collections reverseOrder                 print all the elements available in list again         System out println  The sorted GPA Scores are             for  double number   dArr                System out println  GPA       number                       Output   GPA   3 2 GPA   1 2 GPA   4 7 GPA   3 3 GPA   4 6 The sorted GPA Scores are  GPA   4 7 GPA   4 6 GPA   3 3 GPA   3 2 GPA   1 2

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Java 8   Arrays sort list  comparator reversed       Update  reversed   reverses the specified comparator  Usually  comparators order ascending  so this changes the order to descending

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For 2D arrays to sort in descending order you can just flip the positions of the parameters int     array         1  5        13  1        12  100        12  85      Arrays sort array   a  b  - gt  Integer compare a 1   b 1        for ascending order Arrays sort array   b  a  - gt  Integer compare a 1   b 1        for descending order  Output for descending 12  100 12  85 1  5 13  1

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For array which contains elements of primitives if there is org apache commons lang 3  at disposal easy way to reverse array  after sorting it  is to use   ArrayUtils reverse array

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public double   sortArrayAlgorithm double   array      sort in descending order     for  int i   0  i  lt  array length  i              for  int j   0  j  lt  array length  j                  if  array i   gt   array j                     double x   array i                   array i    array j                   array j    x                                    return array      just use this method to sort an array of type double in descending order  you can use it to sort arrays of any other types like int  float  and etc  just by changing the  return type   the  argument type  and the variable  x  type to the corresponding type  you can also change      to   lt    in the if condition to make the order ascending

[java] Java Array Sort descending?

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