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


How to sort objects of user defined data type?
Please refer Arrays.sort() in Java and Collections.sort() in Java for examples.

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