text: /*
   * 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 com.alipay.lookout.api;
  
  import com.alipay.lookout.common.Assert;
  
  import java.util.Arrays;
  
  /**
   * Immutable implementation of Tag.
   * Created by kevin.luy@alipay.com on 2017/1/26.
   */
  public final class BasicTag implements Tag {
  
      private final String key;
      private final String value;
  
      /**
       * create a new basic tag instance.
       *
       * @param key   k
       * @param value v
       */
      public BasicTag(String key, String value) {
          this.key = Assert.notNull(key, "tag key");
          this.value = value == null ? "" : value;
      }
  
      /**
       * 支持自定义类型tag生成标准的BasicTag
       * @param tag tag
       */
      static BasicTag of(Tag tag) {
          return (tag instanceof BasicTag) ? (BasicTag) tag : new BasicTag(tag.key(), tag.value());
      }
  
      @Override
      public String key() {
          return key;
      }
  
      @Override
      public String value() {
          return value;
      }
  
      @Override
      public boolean equals(Object obj) {
          if (this == obj)
              return true;
          if (obj == null || !(obj instanceof BasicTag))
              return false;
          BasicTag tag = (BasicTag) obj;
          return key.equals(tag.key) && value.equals(tag.value);
      }
  
      @Override
      public int hashCode() {
          return Arrays.hashCode(new String[] { key, value });
      }
  
      @Override
      public String toString() {
          return key + '=' + value;
      }
  }
  