Hi Sergey,
Thanks, you are right! I did not realize it copied the array into a local
variable, but that makes sense.
Here is the byte code generated by javac (9) for two different methods:
void x() {
for (Object o : a) {
System.out.println(o);
}
}
0: aload_0
1: getfield #2 // Field a:[Ljava/lang/Object;
4: astore_1
5: aload_1
6: arraylength
7: istore_2
8: iconst_0
9: istore_3
10: iload_3
11: iload_2
12: if_icmpge 34
15: aload_1
16: iload_3
17: aaload
18: astore 4
20: getstatic #3 // Field
java/lang/System.out:Ljava/io/PrintStream;
23: aload 4
25: invokevirtual #4 // Method
java/io/PrintStream.println:(Ljava/lang/Object;)V
28: iinc 3, 1
31: goto 10
34: return
void y() {
Object[] a = this.a;
for (Object o : a) {
System.out.println(o);
}
}
0: aload_0
1: getfield #2 // Field a:[Ljava/lang/Object;
4: astore_1
5: aload_1
6: astore_2
7: aload_2
8: arraylength
9: istore_3
10: iconst_0
11: istore 4
13: iload 4
15: iload_3
16: if_icmpge 39
19: aload_2
20: iload 4
22: aaload
23: astore 5
25: getstatic #3 // Field
java/lang/System.out:Ljava/io/PrintStream;
28: aload 5
30: invokevirtual #4 // Method
java/io/PrintStream.println:(Ljava/lang/Object;)V
33: iinc 4, 1
36: goto 13
39: return
Paul.
On Mar 17, 2014, at 5:07 PM, Sergey Bylokhov <sergey.bylok...@oracle.com> wrote:
> On 3/17/14 7:41 PM, Paul Sandoz wrote:
>> On Mar 15, 2014, at 12:17 AM, Ulf Zibis <ulf.zi...@cosoco.de> wrote:
>>
>>> Am 14.03.2014 17:10, schrieb Paul Sandoz:
>>>>> I'm willing to believe for-loop over array is as efficient as
>>>>> fortran-style loop
>>>>>
>>>>> + for (E e : a) {
>>>>> + action.accept(e);
>>>>> + }
>>>>>
>>>> Yeah, i previously went through a whole bunch of code replacing such
>>>> fortran-style loops with 'foreach' style based on automated code analysis.
>>> But wouldn't this help a little more? :
>>> + final E[] a = this.a;
>>> + for (E e : a) {
>>> + action.accept(e);
>>> + }
>>>
>> Thanks, i changed it to that.
> ? Why this line is needed:
> final E[] a = this.a;
> Since according to specification foreach over array should be transformed to:
> JLS 14.14.2:
> T[] #a = Expression;
> L1: L2: ... Lm:
> for (int #i = 0; #i < #a.length; #i++) {
> VariableModifiersopt TargetType Identifier = #a[#i];
> Statement
> }
>
> So your code will be transformed to:
> + final E[] a = this.a;
> + E[] #a = a;
> + for (E e : #a) {
> + action.accept(e);
> + }
> Or I miss something?
>>> I more like the given style with less spaces:
>>> 3854 for (int i=0; i<a.length; i++)
>>> It better visualizes the 3 parts of the for statement.
>>>
>> Subjectively that irritates my eyes :-) non-subjectively it is
>> inconsistently applied.
>>
>> Paul.
>
>
> --
> Best regards, Sergey.
