guava/src/com/google/common/util/concurrent/AtomicLongMap.java
@CanIgnoreReturnValue
  public long addAndGet(K key, long delta) {
    return accumulateAndGet(key, delta, Long::sum);
  }
@CanIgnoreReturnValue
  public long addAndGet(K key, long delta) {
    return accumulateAndGet(key, delta, Long::sum);
  }
@ CanIgnoreReturnValue public long addAndGet ( K key , long delta ) { return accumulateAndGet ( key , delta , Long :: sum ) ; }
Adds {@code delta} to the value currently associated with {@code key}, and returns the new
value.
Adds {