content: /**
   * Licensed 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.aurora.common.stats;
  
  /**
   * A convenience class to perform the basic tasks needed for a {@link RecordingStat} except the
   * actual value calculation.
   *
   * @author William Farner
   */
  public abstract class SampledStat<T extends Number> extends StatImpl<T> implements RecordingStat<T> {
  
    private volatile T prevValue;
  
    public SampledStat(String name, T defaultValue) {
      super(name);
      this.prevValue = defaultValue; /* Don't forbid null. */
    }
  
    public abstract T doSample();
  
    @Override
    public final T sample() {
      prevValue = doSample();
      return prevValue;
    }
  
    @Override
    public T read() {
      return prevValue;
    }
  }
  