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Date: Mon, 27 Sep 2010 10:58:35 +0100
From: Oliver Deakin <oliver.deakin@googlemail.com>
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To: dev@harmony.apache.org
Subject: Re: [classlib][luni] String.concat() behaves differently to the spec
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  Committed with regression test at r1001652.

Regards,
Oliver

On 24/09/2010 14:37, Oliver Deakin wrote:
>  Hi all,
>
> For String.concat(), the spec says:
>
> "If the length of the argument string is 0, then this String object is 
> returned. Otherwise, a new String object is created, representing a 
> character sequence that is the concatenation of the character sequence 
> represented by this String object and the character sequence 
> represented by the argument string."
>
> On Harmony the following test prints "Returned the same String":
>
> public class Test {
>     public static void main(String[] args) {
>         String s1 = "";
>         String s2 = "s2";
>         String s3 = s1.concat(s2);
>         if(s3 == s2)
>             System.out.println("Returned the same String");
>     }
> }
>
> This is because in Harmony's String.concat() we check for both the 
> parameter string and "this" to have length >0 before we do a 
> concatenation, otherwise we just return one or the other of the 
> Strings. On the RI it does not print anything, which agrees with the 
> spec as far as I can see. To match the spec here, we just need to 
> modify concat to create a new String in all cases except when 
> string.count==0 [1]. Since String is a sensitive class, I thought I'd 
> run this by the list before I committed it. Any comments?
>
> Regards,
> Oliver
>
> [1]
> Index: String.java
> ===================================================================
> --- String.java    (revision 1000855)
> +++ String.java    (working copy)
> @@ -678,14 +678,17 @@
>       *         specified string.
>       */
>      public String concat(String string) {
> -        if (string.count > 0 && count > 0) {
> -            char[] buffer = new char[count + string.count];
> +        if (string.count == 0) {
> +            return this;
> +        }
> +
> +        char[] buffer = new char[count + string.count];
> +        if (count > 0) {
>              System.arraycopy(value, offset, buffer, 0, count);
> -            System.arraycopy(string.value, string.offset, buffer, count,
> -                    string.count);
> -            return new String(0, buffer.length, buffer);
>          }
> -        return count == 0 ? string : this;
> +        System.arraycopy(string.value, string.offset, buffer, count,
> +                string.count);
> +        return new String(0, buffer.length, buffer);
>      }
>
>      /**
>
>

-- 
Oliver Deakin
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