Hi,
I would like to thank all people in discussion, especially Chris.
I had never looked at bytecodes before. As far as I see the
call to the String constructor is in the line 3.
It is interesting to know how different bytecodes could be in
different compilers.
Regards,
Jacob Nikom
Chris Abbey wrote:
> At 01:45 9/8/00 +0200, Uli Luckas wrote:
> >Now the second bad news, if you decompile the code generated with either
> >javac or jikes you can see that the constructor call is really compiled
> >into the code.
>
> umm... no it isn't....
>
> test.java:
> public class test {
> public static void main (String[] args) {
> String a = "aaa";
> String b = new String("bbb");
> System.out.println("---");
> System.out.println(a);
> System.out.println(b);
> }
> }
>
> Jikes produced bytecode:
> Method void main(java.lang.String[])
> 0 ldc #9 <String "aaa">
> 2 astore_1
> 3 new #11 <Class java.lang.String>
> 6 dup
> 7 ldc #13 <String "bbb">
> 9 invokespecial #18 <Method java.lang.String(java.lang.String)>
> 12 astore_2
> 13 getstatic #22 <Field java.io.PrintStream out>
> 16 ldc #25 <String "---">
> 18 invokevirtual #29 <Method void println(java.lang.String)>
> 21 getstatic #22 <Field java.io.PrintStream out>
> 24 aload_1
> 25 invokevirtual #29 <Method void println(java.lang.String)>
> 28 getstatic #22 <Field java.io.PrintStream out>
> 31 aload_2
> 32 invokevirtual #29 <Method void println(java.lang.String)>
> 35 return
>
> as you can clearly see there is only one call to the String ctor,
> and that is for b not a. Doing otherwise would be a violation of
> the VM spec. Javac in 118 and 130 emit similar bytecode.
>
> Jacob, another point I forgot to mention in my offlist reply was
> that duplicating a String in java is potentially more than a byte
> array copy... Strings have to be "internalized" which isn't always
> cheap in either time or resources.
>
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