RFR: 8202719: Use Collections.emptyEnumeration() where possible

[Claes Redestad]

Hi,

I'll sponsor this trivial contribution.

Bug: https://bugs.openjdk.java.net/browse/JDK-8202719

Webrev: http://cr.openjdk.java.net/~redestad/8202719/open.00/

Thanks!

/Claes

On 2018-05-07 14:35, Claes Redestad wrote:
> Hi, looks like a reasonable cleanup.
>
> I would expect very few applications actually use these, but at the
> very least we'd save a few bytes of compiled bytecode.
>
> /Claes
>
> On 2018-05-06 17:19, Christoph Dreis wrote:
>> Hi,
>>
>> I just noticed two places - namely in JarFile and JarVerifier - that 
>> could
>> make use of Collections.emptyEnumeration().
>>
>> Let me know what you think. I'd be happy if this is sponsored in case 
>> it's
>> considered worthwile.
>>
>> Cheers,
>> Christoph
>>
>> ============= PATCH ==============
>> diff -r 7238cb613dc5 
>> src/java.base/share/classes/java/util/jar/JarFile.java
>> --- a/src/java.base/share/classes/java/util/jar/JarFile.java Sun May 06
>> 00:42:59 2018 +0200
>> +++ b/src/java.base/share/classes/java/util/jar/JarFile.java Sun May 06
>> 17:10:42 2018 +0200
>> @@ -42,6 +42,7 @@
>>   import java.security.CodeSource;
>>   import java.security.cert.Certificate;
>>   import java.util.ArrayList;
>> +import java.util.Collections;
>>   import java.util.Enumeration;
>>   import java.util.List;
>>   import java.util.Locale;
>> @@ -1095,16 +1096,7 @@
>>           if (includeUnsigned) {
>>               return unsignedEntryNames();
>>           } else {
>> -            return new Enumeration<>() {
>> -
>> -                public boolean hasMoreElements() {
>> -                    return false;
>> -                }
>> -
>> -                public String nextElement() {
>> -                    throw new NoSuchElementException();
>> -                }
>> -            };
>> +            return Collections.emptyEnumeration();
>>           }
>>       }
>>
>> diff -r 7238cb613dc5
>> src/java.base/share/classes/java/util/jar/JarVerifier.java
>> --- a/src/java.base/share/classes/java/util/jar/JarVerifier.java Sun
>> May 06 00:42:59 2018 +0200
>> +++ b/src/java.base/share/classes/java/util/jar/JarVerifier.java Sun
>> May 06 17:10:42 2018 +0200
>> @@ -684,7 +684,7 @@
>>           }
>>
>>           final List<CodeSigner[]> signersReq = req;
>> -        final Enumeration<String> enum2 = (matchUnsigned) ?
>> unsignedEntryNames(jar) : emptyEnumeration;
>> +        final Enumeration<String> enum2 = matchUnsigned ?
>> unsignedEntryNames(jar) : Collections.emptyEnumeration();
>>
>>           return new Enumeration<>() {
>>
>> @@ -769,16 +769,6 @@
>>               }
>>           };
>>       }
>> -    private Enumeration<String> emptyEnumeration = new
>> Enumeration<String>() {
>> -
>> -        public boolean hasMoreElements() {
>> -            return false;
>> -        }
>> -
>> -        public String nextElement() {
>> -            throw new NoSuchElementException();
>> -        }
>> -    };
>>
>