How to reverse int array Java

Question

I've been trying to take a pre-made array of 100 random integers and reverse it. I'm not getting any error messages, but the resulting array is only reversed about halfway before it restarts. This has been messing up the results and I can't seem to find out what's wrong with it. I'm pretty new to Java so I have the feeling it's a simple mistake that I haven't found yet, so I'd appreciate any help or advice. For reference here's the method I created:

//create a method to reverse the array
  public static void makeNewArray(){
    System.out.println("\nReversed Array:\n");

     //use a for loop to traverse the array
        for(int i=numArray.length-1;i>=0;i--){
          int temp = numArray[i];
          numArray[i] = numArray[numArray.length - i - 1];
          numArray[numArray.length - i - 1] = temp;
          //print the reversed array
          System.out.print("index " + (i+1) + ": "+ numArray[i] + ", ");
        }
  }

You can make a stream from your array and reverse it with a one-liner accepted answer [here](https://stackoverflow.com/questions/24010109/java-8-stream-reverse-order). — Water, Oct 25 '21 at 23:49
At each iteration of the loop, you swap two elements. As a result, the array is completely reversed when you reach the midpoint. Then, as the loop continues, it swaps everything back into the original order. — John Bollinger, Oct 25 '21 at 23:51
You are iterating the entire length of the array; you only need to iterate to the midpoint of the array. — Ezward, Oct 25 '21 at 23:51
you are going all the way through the array, when you should stop half way. Each step you flip the first and last, the second and second to last, the third and third to last and so on, so that by the time you are half way you are done, except you keep going filliping it all back to the way it was — Jacob Glik, Oct 25 '21 at 23:58
Okay, thanks for all your advice, I made sure to only iterate over half of the array like you all had mentioned and it worked great. thank you so much for the help! — rj7699, Oct 26 '21 at 00:25

score 2 · Accepted Answer · answered Oct 26 '21 at 00:12

In the for-loop you are flipping the first number and the last number, the second number and the second-to-last number, the third number and the third-to-last number, and so on. If you go from start to the end you will flip each number twice, because you move fully though the array, and flip two numbers, therefore flipping twice the numbers in the array. You must only traverse half the array, ex:

int counter = 0;
for(int i = numArray.length-1; i >= counter; i--){
    int temp = numArray[i];
    numArray[i] = numArray[numArray.length - i - 1];
    numArray[numArray.length - i - 1] = temp;
    //print the reversed array
    //System.out.print("index " + (i) + ": "+ numArray[i] + ", ");
    counter++;
}

//print arr
// must be separate because must iterate the whole array
for(int i = 0; i < numArray.length; ++i){ 
    System.out.print("Index: "+i+": "+numArray[i]+", ");
}
System.out.println(""); // end code with newline

How to reverse int array Java

1 Answers1