I've been using Guava's ImmutableMap
with a Builder
for awhile without giving much thought to how/why it works. I've been using the builder in the way described by the Javadoc:
ImmutableMap<String, Integer> WORD_TO_INT =
new ImmutableMap.Builder<String, Integer>()
.put("one", 1)
.put("two", 2)
.put("three", 3)
.build();
I've also seen examples elsewhere on SO of this syntax:
ImmutableMap<String,Integer> myMap = ImmutableMap.<String, Integer>builder()
.put("one", 1)
.put("two", 2)
.put("three", 3)
.build();
Both seem to produce the exact same result.
A quick glance at the ImmutableMap
source shows that the static builder()
call in the 2nd example returns: new Builder<K, V>()
There doesn't appear to be any functional difference between the two methods.
Is there any difference under the hood? Any reason to prefer one or the other?
EDIT: Adding bytecode difference.
The bytecode generated is almost identical except for one line:
Method 1(Builder<K,V>
):
static {};
0 new com.google.common.collect.ImmutableMap$Builder [12]
3 dup
4 invokespecial com.google.common.collect.ImmutableMap$Builder() [14]
7 ldc <String "key1"> [17]
........
Method 2:(<K,V>builder()
)
static {};
0 invokestatic com.google.common.collect.ImmutableMap.builder() : com.google.common.collect.ImmutableMap$Builder [12]
3 ldc <String "key1"> [18]
........
After that they're pretty much the same, the first line being different makes sense given the source differences, but I'm not sure why the first one calls dup
and the second doesn't.