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Apache Hadoop Common
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/**
 * 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.hadoop.metrics2;

import com.google.common.base.Objects;
import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;

import java.util.StringJoiner;

import static com.google.common.base.Preconditions.checkNotNull;

/**
 * The immutable metric
 */
@InterfaceAudience.Public
@InterfaceStability.Evolving
public abstract class AbstractMetric implements MetricsInfo {
  private final MetricsInfo info;

  /**
   * Construct the metric
   * @param info  about the metric
   */
  protected AbstractMetric(MetricsInfo info) {
    this.info = checkNotNull(info, "metric info");
  }

  @Override public String name() {
    return info.name();
  }

  @Override public String description() {
    return info.description();
  }

  protected MetricsInfo info() {
    return info;
  }

  /**
   * Get the value of the metric
   * @return the value of the metric
   */
  public abstract Number value();

  /**
   * Get the type of the metric
   * @return the type of the metric
   */
  public abstract MetricType type();

  /**
   * Accept a visitor interface
   * @param visitor of the metric
   */
  public abstract void visit(MetricsVisitor visitor);

  @Override public boolean equals(Object obj) {
    if (obj instanceof AbstractMetric) {
      final AbstractMetric other = (AbstractMetric) obj;
      return Objects.equal(info, other.info()) &&
             Objects.equal(value(), other.value());
    }
    return false;
  }

  @Override public int hashCode() {
    return Objects.hashCode(info, value());
  }

  @Override
  public String toString() {
    return new StringJoiner(", ", this.getClass().getSimpleName() + "{", "}")
        .add("info=" + info)
        .add("value=" + value())
        .toString();
  }
}