synchronized (mutex) {
        return typePreservingCollection(delegate().get(key), mutex);
      }
    }

    @Override
    public boolean put(@ParametricNullness K key, @ParametricNullness V value) {
      synchronized (mutex) {
        return delegate().put(key, value);
      }
    }

    @Override
    public boolean putAll(@ParametricNullness K key, Iterable<? extends V> values) {

            @SuppressWarnings("unchecked")
            E result = (E) canonical;
            return result;
          }
        }

        // didn't see it, trying to put it instead...
        Dummy sneaky = map.putIfAbsent(sample, Dummy.VALUE);
        if (sneaky == null) {
          return sample;
        } else {
          /* Someone beat us to it! Trying again...
           *

     * valueEquivalence.
     */

    @Override
    public V setValue(V newValue) {
      put(getKey(), newValue);
      return super.setValue(newValue); // done after put() so that it happens only if put() succeeds
    }
  }

  final class EntryIterator extends HashIterator<Entry<K, V>> {

    @Override
    public Entry<K, V> next() {

//
// In general, an S3 ETag is an MD5 checksum of the object
// content. However, there are many exceptions to this rule.
//
// # Single-part Upload
//
// In case of a basic single-part PUT operation - without server
// side encryption or object compression - the ETag of an object
// is its content MD5.
//
// # Multi-part Upload
//
// The ETag of an object does not correspond to its content MD5

		// Put an empty object with a trailing slash
		30: {bucketName: bucket, objName: "emptydir/", inputData: []byte{}, expectedMd5: getMD5Hash([]byte{})},
		// Put an object inside the empty directory
		31: {bucketName: bucket, objName: "emptydir/" + object, inputData: data, inputDataSize: int64(len(data)), expectedMd5: getMD5Hash(data)},

這裡的「操作」指的是 HTTP 的「方法」之一。

其中包括：

* `POST`
* `GET`
* `PUT`
* `DELETE`

……以及更少見的：

* `OPTIONS`
* `HEAD`
* `PATCH`
* `TRACE`

在 HTTP 協定中，你可以使用這些「方法」之一（或更多）與每個路徑進行通信。

---

在建置 API 時，你通常使用這些特定的 HTTP 方法來執行特定的動作。

通常你使用：

* `POST`：用來建立資料。
* `GET`：用來讀取資料。
* `PUT`：用來更新資料。
* `DELETE`：用來刪除資料。

所以，在 OpenAPI 中，每個 HTTP 方法都被稱為「操作」。

    return delegate.pollFirstEntry();
  }

  @Override
  public @Nullable Entry<K, V> pollLastEntry() {
    return delegate.pollLastEntry();
  }

  @Override
  public @Nullable V put(K key, V value) {
    return delegate.put(checkValid(key), value);
  }

  @Override
  public void putAll(Map<? extends K, ? extends V> map) {
    for (K key : map.keySet()) {
      checkValid(key);
    }

            @SuppressWarnings("unchecked")
            E result = (E) canonical;
            return result;
          }
        }

        // didn't see it, trying to put it instead...
        Dummy sneaky = map.putIfAbsent(sample, Dummy.VALUE);
        if (sneaky == null) {
          return sample;
        } else {
          /* Someone beat us to it! Trying again...
           *

 *
 * <p><b>Warning:</b> The methods of {@code ForwardingSortedMap} forward <i>indiscriminately</i> to
 * the methods of the delegate. For example, overriding {@link #put} alone <i>will not</i> change
 * the behavior of {@link #putAll}, which can lead to unexpected behavior. In this case, you should
 * override {@code putAll} as well, either providing your own implementation, or delegating to the

		SendContentMd5: true,
		StorageClass:   s3.StorageClass,
		UserMetadata:   meta,
	})
	return remoteVersionID(res.VersionID), s3.ToObjectError(err, object)
}

func (s3 *warmBackendS3) Put(ctx context.Context, object string, r io.Reader, length int64) (remoteVersionID, error) {
	return s3.PutWithMeta(ctx, object, r, length, map[string]string{})
}