Java Collections sort() Method

The sort() method of Java Collections class is used to sort the elements presents in the specified list. There is two different types of Java sort() method which can be differentiated depending on its parameter. These are:

Java Collections sort(list) Method
Java Collections sort(list, comp) Method

Java Collections sort(list) Method

This method is used to sort the elements presents in the specified list of collection in ascending order.

Java Collections sort(list, comp) Method

This method is used to sorts the specified list according to the order introduced by the specified comparator.

Syntax

Following is the declaration of sort() ~~method:~~

public static <T extends Comparable<? super T>> void sort(List<T> list) public static <T> void sort(List<T> list, Comparator<? super T> comp)
Parameter
Parameter Description Required/Optional
list It is the list which will be sorted. Required
comp It is the comparator which determines the order of the list. Required
Returns
The sort() method does not return anything.
Exceptions
UnsupportedOperationException- This method thrown exception if the specified list or its list-iterator does not support the set operation.
ClassCastException- This method thrown exception if the list contains elements that are not mutually comparable (for example, strings and integers).
Example 1
import java.util.*; public class CollectionsSortExample1 { public static void main(String[] args) { //Create an array of string objects String str[] = { "Java","Python","Android","One","Ruby","Node.js"}; //Create list List<String> list = new ArrayList<>(Arrays.asList(str)); System.out.println("Specified value before sort: "+list); //Sort the list Collections.sort(list); System.out.println("Specified value after sort: "+list); } }
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Output:
Specified value before sort: [Java, Python, Android, One, Ruby, Node.js] Specified value after sort: [Android, Java, Node.js, One, Python, Ruby]
Example 2
import java.util.*; public class CollectionsSortExample2 { public static void main(String[] args) { //Create an array of string objects String str[] = { "Java","Python","Android","One","Ruby","Node.js"}; //Create list List<String> list = new ArrayList<>(Arrays.asList(str)); System.out.println("Value before sort: "+list); //Sort the list according to specified comparator Collections.sort(list,Collections.reverseOrder()); System.out.println("Sort Value according to specified comparator: "+list); } }
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Output:
Value before sort: [Java, Python, Android, One, Ruby, Node.js] Sort Value according to specified comparator: [Ruby, Python, One, Node.js, Java, Android]
Example 3
import java.util.*; public class CollectionsSortExample3 { public static void main(String[] args) { ArrayList<Integer> al=new ArrayList<>(); al.add(Integer.valueOf(201)); al.add(Integer.valueOf(101)); al.add(230);//internally will be converted into objects as Integer.valueOf(230) Collections.sort(al); Iterator<Integer> itr=al.iterator(); while(itr.hasNext()){ System.out.println(itr.next()); } } }
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Output:
101 201 230
Example 4
import java.util.*; public class CollectionsSortExample4 { public static void main (String[] args) { ArrayList<Student> arr = new ArrayList<Student>(); arr.add(new Student(101, "Java", "USA")); arr.add(new Student(103, "Ruby", "China")); arr.add(new Student(102, "Android", "India")); System.out.println("Data before sorted-"); for (int i=0; i<arr.size(); i++) System.out.println(arr.get(i)); //Sorting data according to specified comparator Collections.sort(arr, new Sortbyroll()); System.out.println("Data after sorted by rollno-"); for (int i=0; i<arr.size(); i++) System.out.println(arr.get(i)); } } //Class which represents a student data. class Student { int rollno; String name, address; //Constructor public Student(int rollno, String name, String address) { this.rollno = rollno; this.name = name; this.address = address; } //Prints student data public String toString() { return this.rollno + " " + this.name + " " + this.address; } } class Sortbyroll implements Comparator<Student> { //Used for sorting in ascending order of roll number public int compare(Student a, Student b) { return a.rollno - b.rollno; } }
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Output:
Data before sorted- 101 Java USA 103 Ruby China 102 Android India Data after sorted by rollno- 101 Java USA 102 Android India 103 Ruby China

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