With this example we are going to demonstrate how to reverse the order of a List. This is provided by the reverse(List list) API method of the Collections class. The ArrayList is used as a List implementation, but the same API applies to any type of List implementation classes e.g. Vector etc. In short, to reverse the order of a List you should:
- Create a new ArrayList.
- Populate the list with elements, with the
add(E e)API method of the ArrayList. - Reverse the elements of the list, invoking the
reverse(List list)API method of the Collections.
Let’s take a look at the code snippet that follows:
package com.javacodegeeks.snippets.core;
import java.util.ArrayList;
import java.util.Collections;
public class ReverseListOrder {
public static void main(String[] args) {
/*
Please note that the same API applies to any type of
List implementation classes e.g. Vector etc
*/
// Create an ArrayList and populate it with elements
ArrayList arrayList = new ArrayList();
arrayList.add("element_1");
arrayList.add("element_2");
arrayList.add("element_3");
arrayList.add("element_4");
arrayList.add("element_5");
System.out.println("ArrayList elements : " + arrayList);
// static void reverse(List list) method reverses the order of elements of the specified list.
Collections.reverse(arrayList);
System.out.println("ArrayList elements after reversing order : " + arrayList);
}
}
Output:
ArrayList elements : [element_1, element_2, element_3, element_4, element_5]
ArrayList elements after reversing order : [element_5, element_4, element_3, element_2, element_1]
This was an example of how to reverse the order of a List in Java.
