How do I reverse an int array in Java?

Question

I am trying to reverse an int array in Java.

This method does not reverse the array.

for(int i = 0; i < validData.length; i++) {     int temp = validData[i];     validData[i] = validData[validData.length - i - 1];     validData[validData.length - i - 1] = temp; } 

What is wrong with it?

Answer 1

To reverse an int array, you swap items up until you reach the midpoint, like this:

for(int i = 0; i < validData.length / 2; i++) {     int temp = validData[i];     validData[i] = validData[validData.length - i - 1];     validData[validData.length - i - 1] = temp; } 

The way you are doing it, you swap each element twice, so the result is the same as the initial list.

Answer 2

With Commons.Lang, you could simply use

ArrayUtils.reverse(int[] array) 

Most of the time, it's quicker and more bug-safe to stick with easily available libraries already unit-tested and user-tested when they take care of your problem.