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1   /*
2    * Copyright 2012 The Netty Project
3    *
4    * The Netty Project licenses this file to you under the Apache License,
5    * version 2.0 (the "License"); you may not use this file except in compliance
6    * with the License. You may obtain a copy of the License at:
7    *
8    *   http://www.apache.org/licenses/LICENSE-2.0
9    *
10   * Unless required by applicable law or agreed to in writing, software
11   * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
12   * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
13   * License for the specific language governing permissions and limitations
14   * under the License.
15   */
16  package io.netty.util;
17  
18  /**
19   * Holds {@link Attribute}s which can be accessed via {@link AttributeKey}.
20   *
21   * Implementations must be Thread-safe.
22   */
23  public interface AttributeMap {
24      /**
25       * Get the {@link Attribute} for the given {@link AttributeKey}. This method will never return null, but may return
26       * an {@link Attribute} which does not have a value set yet.
27       */
28      <T> Attribute<T> attr(AttributeKey<T> key);
29  
30      /**
31       * Returns {@code} true if and only if the given {@link Attribute} exists in this {@link AttributeMap}.
32       */
33      <T> boolean hasAttr(AttributeKey<T> key);
34  }