.sort()

The Collections.sort() method sorts a List based on natural ordering or based on a Comparator. To sort based on natural ordering, the elements of the List must implement the Comparable interface.

import java.util.*;

// This sorts by natural ordering
Collections.sort(myList);

// This sorts by a Comparator
Collections.sort(myList, myComparator);

Both methods sort myList. The first sorts myList using the natural ordering of the elements. The second uses myComparator to order the elements.

The following example creates an ArrayList and then uses Collections.sort() to reorder its elements:

import java.util.*;

public class Main {
 public static void main(String[] args) {
   ArrayList<String> food = new ArrayList<String>();
   food.add("Cabbage");
   food.add("Pizza");
   food.add("Sausage");
   food.add("Potatoes");
   food.add("Salad");

   System.out.println(food);
   Collections.sort(food);
   System.out.println(food);
 }
}

This results in the following output:

[Cabbage, Pizza, Sausage, Potatoes, Salad]
[Cabbage, Pizza, Potatoes, Salad, Sausage]