Collections.sort[] in Java with Examples
java.util.Collections.sort[] method is present in java.util.Collections class. It is used to sort the elements present in the specified list of Collection in ascending order.
It works similar to java.util.Arrays.sort[] method but it is better then as it can sort the elements of Array as well as linked list, queue and many more present in it.
Example:
Let us suppose that our list contains {"Geeks For Geeks", "Friends", "Dear", "Is", "Superb"} After using Collection.sort[], we obtain a sorted list as {"Dear", "Friends", "Geeks For Geeks", "Is", "Superb"}Sorting an ArrayList in ascending order
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// Java program to demonstrate working of Collections.sort[]
import java.util.*;
public class Collectionsorting
{
public static void main[String[] args]
{
// Create a list of strings
ArrayList al = new ArrayList[];
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]
Sorting an ArrayList in descending order
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// Java program to demonstrate working of Collections.sort[]
// to descending order.
import java.util.*;
public class Collectionsorting
{
public static void main[String[] args]
{
// Create a list of strings
ArrayList al = new ArrayList[];
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:
Sorting an ArrayList according to user defined criteria.
We can use Comparator Interface for this purpose.
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// Java program to demonstrate working of Comparator
// interface and Collections.sort[] to sort according
// to user defined criteria.
import java.util.*;
import java.lang.*;
import java.io.*;
// A class to represent a student.
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;
}
// Used to print student details in main[]
public String toString[]
{
return this.rollno + " " + this.name +
" " + this.address;
}
}
class Sortbyroll implements Comparator
{
// Used for sorting in ascending order of
// roll number
public int compare[Student a, Student b]
{
return a.rollno - b.rollno;
}
}
// Driver class
class Main
{
public static void main [String[] args]
{
ArrayList ar = new ArrayList[];
ar.add[new Student[111, "bbbb", "london"]];
ar.add[new Student[131, "aaaa", "nyc"]];
ar.add[new Student[121, "cccc", "jaipur"]];
System.out.println["Unsorted"];
for [int i=0; i
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