Reversing integer array

Question

Just curious, but when I try to use this to reverse an array it always spits out some incoherent gibberish instead of the array reversed, such as [I@43256ea2. Any ideas as to why it does this?

public class Fiddle {
    public static void main(String[] args) {
        int[] number = {1,2,3,4,5};
        System.out.println(reverse(number));
    }
    public static int[] reverse(int[] a) {
        int[] b = new int[a.length];
        for (int i = 0; i < a.length; i++) {
            b[a.length-1-i] = a[i];
        }
        return b;
    }
}

Thanks for any ideas as to why this is happening (it's probably because I'm forgetting something though).

your printing binary information. You'll need to convert each entry in the array to ascii before your print. — Jonathan M
– Jonathan M, Commented Apr 11, 2012 at 20:17
Agreed -- but not immediately obvious to me why an array of {5,4,3,2,1} in memory would resolve to "[I@43256ea2". I'm imagining the bytes "00 00 00 05 00 00 00 04 00 00 00 03 etc...". Can anyone shed some light on why we see this specific output string? — Robert Martin
– Robert Martin, Commented Apr 11, 2012 at 20:21

Mark Peters · Accepted Answer · 2012-04-11 20:22:29Z

10

Use the utility method java.util.Arrays.toString(int[]):

System.out.println(Arrays.toString(reverse(number)));

Array classes do not override Object.toString(), meaning they use the default implementation provided by Object, which is "type@hashcode_in_hex". The String representation of the type int[] is [I, which is why you are seeing this "incoherent gibberish."

edited Apr 11, 2012 at 20:22

answered Apr 11, 2012 at 20:17

Mark Peters

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Bohemian · Accepted Answer · 2012-04-11 20:17:19Z

2

Try this:

System.out.println(Arrays.toString(reverse(number)));

It's one of the "mistakes" of java - you have to use Arrays.toString() otherwise you get the default toString() from Object, which produces output like you're seeing,

answered Apr 11, 2012 at 20:17

Bohemian♦

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Comments

Simiil · Accepted Answer · 2012-04-11 20:17:51Z

1

You are printing the hash of the array. you should do something like

for(int i: reverse(number)){
  System.out.println(i);
}

answered Apr 11, 2012 at 20:17

Simiil

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Ryan M. · Accepted Answer · 2012-04-11 20:18:53Z

1

Commons.lang

ArrayUtils.reverse(int[] array)

Done.

answered Apr 11, 2012 at 20:18

Ryan M.

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