Sorting in Java

There are two in-built methods to sort in Java.

1. Arrays.Sort() works for arrays which can be of primitive data type also.
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   // A sample Java program to demonstrate working of // Arrays.sort(). // It by default sorts in ascending order. import java.util.Arrays;    public class GFG {     public static void main(String[] args)     {         int[] arr = { 13, 7, 6, 45, 21, 9, 101, 102 };            Arrays.sort(arr);            System.out.printf("Modified arr[] : %s",                           Arrays.toString(arr));     } }

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   Output:

   Modified arr[] : [6, 7, 9, 13, 21, 45, 101, 102]
   

2. Collections.sort() works for objects Collections like ArrayList and LinkedList.
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   // Java program to demonstrate working of Collections.sort() import java.util.*;    public class GFG {     public static void main(String[] args)     {         // Create a list of strings         ArrayList<String> al = new ArrayList<String>();         al.add("Geeks For Geeks");         al.add("Friends");         al.add("Dear");         al.add("Is");         al.add("Superb");            /* Collections.sort method is sorting the         elements of ArrayList in ascending order. */         Collections.sort(al);            // Let us print the sorted list         System.out.println("List after the use of"                            + " Collection.sort() :\n" + al);     } }

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Output:

List after the use of Collection.sort() :
[Dear, Friends, Geeks For Geeks, Is, Superb]

• Which sorting algorithm does Java use in sort()?
  Java’s Arrays.sort method uses Quicksort for arrays of primitives and merge sort for arrays of objects.
• Which order of sorting is done by default?
  It by default sorts in ascending order.
• How to sort array or list in descending order?
  It can be done with the help of Collections.reverseOrder().

  Example:

  
  
  
  1. For Arrays.sort()
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     // A sample Java program to sort an array // in descending order using Arrays.sort(). import java.util.Arrays; import java.util.Collections;    public class GFG {     public static void main(String[] args)     {         // Note that we have Integer here instead of         // int[] as Collections.reverseOrder doesn't         // work for primitive types.         Integer[] arr = { 13, 7, 6, 45, 21, 9, 2, 100 };            // Sorts arr[] in descending order         Arrays.sort(arr, Collections.reverseOrder());            System.out.printf("Modified arr[] : %s",                           Arrays.toString(arr));     } }

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     Output:

     Modified arr[] : [100, 45, 21, 13, 9, 7, 6, 2]
     

  2. For Collections.sort()
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     // Java program to demonstrate working of Collections.sort() // to descending order. import java.util.*;    public class GFG {     public static void main(String[] args)     {         // Create a list of strings         ArrayList<String> al = new ArrayList<String>();         al.add("Geeks For Geeks");         al.add("Friends");         al.add("Dear");         al.add("Is");         al.add("Superb");            /* Collections.sort method is sorting the         elements of ArrayList in ascending order. */         Collections.sort(al, Collections.reverseOrder());            // Let us print the sorted list         System.out.println("List after the use of"                            + " Collection.sort() :\n" + al);     } }

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     Output:

     List after the use of Collection.sort() :
     [Superb, Is, Geeks For Geeks, Friends, Dear]
     

• How to sort only a subarray?
  Example:
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  // A sample Java program to sort a subarray // using Arrays.sort(). import java.util.Arrays;    public class GFG {     public static void main(String[] args)     {         // Our arr contains 8 elements         int[] arr = { 13, 7, 6, 45, 21, 9, 2, 100 };            // Sort subarray from index 1 to 4, i.e.,         // only sort subarray {7, 6, 45, 21} and         // keep other elements as it is.         Arrays.sort(arr, 1, 5);            System.out.printf("Modified arr[] : %s",                           Arrays.toString(arr));     } }

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  Output:

  Modified arr[] : [13, 6, 7, 21, 45, 9, 2, 100]
  

• How to write my own sorting function in Java?<
  Please see Java programs for Quick Sort, Merge Sort, Insertion Sort, Selection Sort, Heap Sort, Bubble Sort

RishabhPrabhu

Technical Content Engineer