Rewrite ImmutableMap.Builder#build to #buildOrThrow

[EnricSala]

Problem

An ImmutableMap.Builder has two terminal methods which accomplish the same thing: build or buildOrThrow.

The buildOrThrow method should be preferred, because the documentation of build specifies:

Prefer the equivalent method {@link #buildOrThrow()} to make it explicit that the method will throw an exception if there are duplicate keys. The {@code build()} method will soon be deprecated.

Description of the proposed new feature

• Support a stylistic preference.
• Avoid a common gotcha, or potential problem.
  • Make the behavior evident: an exception may be thrown (in case of duplicate keys).
• Improve performance.

I would like to rewrite the following code:

ImmutableMap.Builder<K, V> builder = ImmutableMap.builder();
builder.build();

to:

ImmutableMap.Builder<K, V> builder = ImmutableMap.builder();
builder.buildOrThrow();

[Stephan202]

I filed #1488 and #1489 for this.