456 }
457 }
458 }
459 }
460
461
462 /**
463 * {@inheritDoc}
464 *
465 * @implSpec
466 * The default implementation is equivalent to performing the
467 * following steps for this {@code map}, then returning the
468 * current value or {@code null} if absent:
469 *
470 * <pre> {@code
471 * V oldValue = map.get(key);
472 * V newValue = (oldValue == null) ? value :
473 * remappingFunction.apply(oldValue, value);
474 * if (newValue == null)
475 * map.remove(key);
476 * else if (oldValue == null)
477 * map.remove(key);
478 * else
479 * map.put(key, newValue);
480 * }</pre>
481 *
482 * <p>The default implementation may retry these steps when multiple
483 * threads attempt updates including potentially calling the remapping
484 * function multiple times.
485 *
486 * <p>This implementation assumes that the ConcurrentMap cannot contain null
487 * values and {@code get()} returning null unambiguously means the key is
488 * absent. Implementations which support null values <strong>must</strong>
489 * override this default implementation.
490 *
491 * @throws UnsupportedOperationException {@inheritDoc}
492 * @throws ClassCastException {@inheritDoc}
493 * @throws NullPointerException {@inheritDoc}
494 * @since 1.8
495 */
496 @Override
497 default V merge(K key, V value,
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456 }
457 }
458 }
459 }
460
461
462 /**
463 * {@inheritDoc}
464 *
465 * @implSpec
466 * The default implementation is equivalent to performing the
467 * following steps for this {@code map}, then returning the
468 * current value or {@code null} if absent:
469 *
470 * <pre> {@code
471 * V oldValue = map.get(key);
472 * V newValue = (oldValue == null) ? value :
473 * remappingFunction.apply(oldValue, value);
474 * if (newValue == null)
475 * map.remove(key);
476 * else
477 * map.put(key, newValue);
478 * }</pre>
479 *
480 * <p>The default implementation may retry these steps when multiple
481 * threads attempt updates including potentially calling the remapping
482 * function multiple times.
483 *
484 * <p>This implementation assumes that the ConcurrentMap cannot contain null
485 * values and {@code get()} returning null unambiguously means the key is
486 * absent. Implementations which support null values <strong>must</strong>
487 * override this default implementation.
488 *
489 * @throws UnsupportedOperationException {@inheritDoc}
490 * @throws ClassCastException {@inheritDoc}
491 * @throws NullPointerException {@inheritDoc}
492 * @since 1.8
493 */
494 @Override
495 default V merge(K key, V value,
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