/** Standard constructor. */
  protected AbstractMapBasedMultiset(Map<E, Count> backingMap) {
    checkArgument(backingMap.isEmpty());
    this.backingMap = backingMap;
  }

  /** Used during deserialization only. The backing map must be empty. */
  void setBackingMap(Map<E, Count> backingMap) {
    this.backingMap = backingMap;
  }

  // Required Implementations

  /**
   * {@inheritDoc}
   *

书接上文，多个关联模型这种情况很常见。

特别是用户模型，因为：

* **输入模型**应该含密码
* **输出模型**不应含密码
* **数据库模型**可能需要包含哈希后的密码

/// danger | 危险

不要存储用户的明文密码。始终只存储之后可用于校验的“安全哈希”。

如果你还不了解，可以在[安全性章节](security/simple-oauth2.md#password-hashing)中学习什么是“密码哈希”。

///

## 多个模型 { #multiple-models }

下面的代码展示了不同模型处理密码字段的方式，及使用位置的大致思路：

{* ../../docs_src/extra_models/tutorial001_py310.py hl[7,9,14,20,22,27:28,31:33,38:39] *}

systems is data "<dfn title="also called marshalling, conversion">serialization</dfn>" which is taking data from the code (Python) and converting it into something that can be sent through the network. For example, converting an object containing data from a database into a JSON object. Converting `datetime` objects into strings, etc.

Another big feature needed by APIs is data validation, making sure that the data is valid, given certain parameters. For example, that some field is an `int`,...

 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.hash;

import static com.google.common.hash.Hashing.sha1;
import static com.google.common.io.BaseEncoding.base16;
import static com.google.common.truth.Truth.assertThat;
import static java.nio.charset.StandardCharsets.US_ASCII;
import static org.junit.Assert.assertThrows;

  @Deprecated
  public final Comparator<? super R> rowComparator() {
    /*
     * requireNonNull is safe because the factories require non-null Comparators, which they pass on
     * to the backing collections.
     */
    return requireNonNull(rowKeySet().comparator());
  }

  /**
   * Returns the comparator that orders the columns. With natural ordering, {@link
   * Ordering#natural()} is returned.

import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;
import org.jspecify.annotations.NullMarked;
import org.jspecify.annotations.Nullable;

/**
 * Tests for {@link Maps#transformValues} when the backing map's views have iterators that don't
 * support {@code remove()}.
 *
 * @author Jared Levy
 */
@GwtCompatible
@NullMarked

import java.util.Set;
import org.jspecify.annotations.Nullable;

/**
 * A map which forwards all its method calls to another map. Subclasses should override one or more
 * methods to modify the behavior of the backing map as desired per the <a
 * href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
 *
 * <p><b>Warning:</b> The methods of {@code ForwardingMap} forward <i>indiscriminately</i> to the

  /**
   * Returns a {@link Collector} that accumulates elements into an {@code ImmutableBiMap} whose keys
   * and values are the result of applying the provided mapping functions to the input elements.
   * Entries appear in the result {@code ImmutableBiMap} in encounter order.
   *
   * <p>If the mapped keys or values contain duplicates (according to {@link

    public Builder<R, C, V> put(R rowKey, C columnKey, V value) {
      cells.add(cellOf(rowKey, columnKey, value));
      return this;
    }

    /**
     * Adds the given {@code cell} to the table, making it immutable if necessary. Duplicate key
     * pairs are not allowed and will cause {@link #build} to fail.
     */
    @CanIgnoreReturnValue

                + " result=\\[java.lang.Integer@\\w+]], SettableFuture@\\w+\\[status=PENDING]]]]");

    // Backing futures complete
    Boolean booleanPartial = true;
    futureBoolean.set(booleanPartial);
    // Once the backing futures are done there's a (brief) moment where we know nothing
    assertThat(futureResult.toString()).matches("CombinedFuture@\\w+\\[status=PENDING]");