How do I reverse an array in Java?

Question

I've tried this code but I am unsure as to why it does not work:

    String[] arr = {"A", "B", "C", "D", "E"};//AD
    String[] arr2 = arr;
    int last = arr.length-1;
    int first = 0;
    int size = arr.length;
    while (first < size) {
        arr2[first] = arr[last];
        last--;
        first++;
    }
    System.out.print(Arrays.toString(arr2));

Can anybody help?

String[] arr2 = arr; doesn't make a copy. That's still the same array. — user2357112
– user2357112, Commented Oct 2, 2017 at 0:07
"String[] arr2 = arr;" - What Harry Potter style magic do you expect here to happen? — Tom
– Tom, Commented Oct 2, 2017 at 0:07
Just make a brand new array of the same length and fill it backwards — TheCrzyMan
– TheCrzyMan, Commented Oct 2, 2017 at 0:08
@tom omg I forgot this isn't python and the array changes even after you copy it.... — Marcos Aleman
– Marcos Aleman, Commented Oct 2, 2017 at 0:09
That's not correct. The arrays wouldn't change if you would actually copy them. — Tom
– Tom, Commented Oct 2, 2017 at 0:09

Roddy of the Frozen Peas · Accepted Answer · 2017-10-02 00:16:43Z

2

This line does not do what you think it does: String[] arr2 = arr. This is simply pointing the variable arr2 at the same object reference as arr. So changes in one will show up in the other, since they're effectively the same thing.

In order to reverse an array, you need to iterate through the array and copy the values to your reversed array.

String[] arr = { "A", "B", "C", "D", "E" };
String[] reversed = new String[arr.length];

for(int i = 0, j = arr.length-1 ; i < arr.length; i++, j--) {
  reversed[j] = arr[i];
}

answered Oct 2, 2017 at 0:16

Roddy of the Frozen Peas

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4 Comments

Jigar Joshi Over a year ago

You could do it in place

Roddy of the Frozen Peas Over a year ago

Feel free to add your own answer showing how to reverse an array in place into a new variable without modifying the original.

Marcos Aleman Over a year ago

Wow, I didn't even know you could do that with a for loop, so cool!

Marcos Aleman Over a year ago

I feel like to do it in place with the same variable you would have to copy the value that you are going to be switching into a temp variable and then put it back.

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