content: /*
   * Licensed to the Apache Software Foundation (ASF) under one
   * or more contributor license agreements.  See the NOTICE file
   * distributed with this work for additional information
   * regarding copyright ownership.  The ASF licenses this file
   * to you under the Apache License, Version 2.0 (the
   * "License"); you may not use this file except in compliance
   * with the License.  You may obtain a copy of the License at
   *
   *     http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  package org.apache.beam.runners.core;
  
  import java.io.IOException;
  
  /**
   * A namespace used for scoping state stored with {@link StateInternals}.
   *
   * <p>Instances of {@link StateNamespace} are guaranteed to have a {@link Object#hashCode} and
   * {@link Object#equals} that uniquely identify the namespace.
   */
  public interface StateNamespace {
  
    /**
     * Return a {@link String} representation of the key. It is guaranteed that this {@link String}
     * will uniquely identify the key.
     *
     * <p>This will encode the actual namespace as a {@link String}. It is preferable to use the
     * {@link StateNamespace} object when possible.
     *
     * <p>The string produced by the standard implementations will not contain a '+' character. This
     * enables adding a '+' between the actual namespace and other information, if needed, to separate
     * the two.
     */
    String stringKey();
  
    /** Append the string representation of this key to the {@link Appendable}. */
    void appendTo(Appendable sb) throws IOException;
  
    /**
     * Return an {@link Object} to use as a key in a cache.
     *
     * <p>Different namespaces may use the same key in order to be treated as a unit in the cache. The
     * {@link Object}'s {@link Object#hashCode} and {@link Object#equals} methods will be used to
     * determine equality.
     */
    Object getCacheKey();
  }
  