ReturnValueIgnored
Return value of this method must be used

Alternate names: ResultOfMethodCallIgnored, CheckReturnValue

The problem

Certain library methods do nothing useful if their return value is ignored. For example, String.trim() has no side effects, and you must store the return value of String.intern() to access the interned string. This check encodes a list of methods in the JDK whose return value must be used and issues an error if they are not.

Optional.orElseThrow

Don’t call orElseThrow just for its side-effects. When the result of a call to orElseThrow is discarded, it may be unclear to future readers whether the result is being discarded deliberately or accidentally. That is, avoid:

// return value of orElseThrow() is silently ignored here
optional.orElseThrow(() -> new AssertionError("something has gone terribly wrong"));

Instead of calling orElseThrow for its side-effects, prefer an explicit call to isPresent(), or use one of checkState or checkArgument from Guava’s Preconditions class.

if (!optional.isPresent()) {
  throw new AssertionError("something has gone terribly wrong");
}

checkState(optional.isPresent(), "something has gone terribly wrong");

checkArgument(optional.isPresent(), "something has gone terribly wrong");

Suppression

Suppress false positives by adding the suppression annotation @SuppressWarnings("ReturnValueIgnored") to the enclosing element.