Guava ImmutableMap Builder syntax

Question

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 WORD_TO_INT = new ImmutableMap.Builder() .put("one", 1) .put("two", 2) .put("three", 3) .build(); ``` I've also seen examples elsewhere on SO of this syntax: ``` ImmutableMap myMap = ImmutableMap.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()` 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`): ``` stati…

Accepted Answer

No, they are identical. The reason for the first syntax is that it makes a nice one-liner.

The reason for the second syntax is the you might have a loop or other flow control, you may need to pass the `Builder` around.

For example:

```
public static void main(final String[] args) throws Exception {
    final ImmutableList.Builder<Integer> lb = ImmutableList.builder();
    for (final String arg : args) {
        lb.add(Integer.parseInt(arg));
    }
}
```

And before you say it, yes a `FluentIterable` would probably be better in this case - but it's just an example.

Guava ImmutableMap Builder syntax

Solution

Problem

Related problems