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Java Reverse ArrayList

Submitted by Deepthi on Sat, 11/13/2010 - 18:48

This Java ArrayList Reverse example shows how to reverse elements of Java ArrayList.

import java.util.ArrayList;
 
//Java Reverse ArrayList
 
/*
 * This Java Reverse ArrayList shows how to reverse ArrayList without using new
 * ArrayList object.
 */
public class JavaReverseArrayList {
    
    public static void main(String args[]){
       
        //create new ArrayList
        ArrayList<String> alistNumbers = new ArrayList<String>();
        alistNumbers.add("1");
        alistNumbers.add("2");
        alistNumbers.add("3");
        alistNumbers.add("4");
        alistNumbers.add("5");
       
        System.out.println("ArrayList before reverse: " + alistNumbers);
       
        String temp = null;
        for(int start=0, end = alistNumbers.size()-1; start < end ; start++, end--){
    
            //swap the first and last element
            temp = alistNumbers.get(start);
            alistNumbers.set(start, alistNumbers.get(end));
            alistNumbers.set(end, temp);
           
        }
       
        System.out.println("ArrayList after reverse: " + alistNumbers);
    }
}
 
/*
Output of above given Java ArrayList Reverse example would be
ArrayList before reverse: [1, 2, 3, 4, 5]
ArrayList after reverse: [5, 4, 3, 2, 1]
*/

Deepthi's blog

may i know why we need to

Submitted by Anonymous on Mon, 12/06/2010 - 20:29.

may i know why we need to swap first and last element? what is the logic behind this ?

Well, If you need to reverse

Submitted by Anonymous on Tue, 12/07/2010 - 13:19.

Well, If you need to reverse elements of an ArrayList, i.e. first element should become last element, then last element will automatically become first. Consider arraylist with just 2 elements, what happen when you make first element last? Wouldn't it also make the last element first automatically?