content: package org.apache.lucene.util;
  
  import java.util.concurrent.atomic.AtomicLong;
  
  /**
   * 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.
   */
  
  /**
   * Simple counter class
   * 
   * @lucene.internal
   * @lucene.experimental
   */
  public abstract class Counter {
  
    /**
     * Adds the given delta to the counters current value
     * 
     * @param delta
     *          the delta to add
     * @return the counters updated value
     */
    public abstract long addAndGet(long delta);
  
    /**
     * Returns the counters current value
     * 
     * @return the counters current value
     */
    public abstract long get();
  
    /**
     * Returns a new counter. The returned counter is not thread-safe.
     */
    public static Counter newCounter() {
      return newCounter(false);
    }
  
    /**
     * Returns a new counter.
     * 
     * @param threadSafe
     *          <code>true</code> if the returned counter can be used by multiple
     *          threads concurrently.
     * @return a new counter.
     */
    public static Counter newCounter(boolean threadSafe) {
      return threadSafe ? new AtomicCounter() : new SerialCounter();
    }
  
    private final static class SerialCounter extends Counter {
      private long count = 0;
  
      @Override
      public long addAndGet(long delta) {
        return count += delta;
      }
  
      @Override
      public long get() {
        return count;
      };
    }
  
    private final static class AtomicCounter extends Counter {
      private final AtomicLong count = new AtomicLong();
  
      @Override
      public long addAndGet(long delta) {
        return count.addAndGet(delta);
      }
  
      @Override
      public long get() {
        return count.get();
      }
  
    }
  }
  