content: /**
   * 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 storm.trident.operation.builtin;
  
  import java.util.Map;
  import storm.trident.operation.Filter;
  import storm.trident.operation.TridentOperationContext;
  import storm.trident.tuple.TridentTuple;
  
  /**
   * A `Filter` implementation that inverts another delegate `Filter`.
   *
   * The `Negate.isKeep()` method simply returns the opposite of the delegate's `isKeep()` method:
   *
   * ```java
   * public boolean isKeep(TridentTuple tuple) {
   *      return !this.delegate.isKeep(tuple);
   * }
   * ```
   *
   * The `Negate` filter is useful for dividing a Stream in two based on some boolean condition.
   *
   * Suppose we had a Stream named `userStream` containing information about users, and a custom `Filter` implementation,
   * `RegisteredUserFilter` that filtered out unregistered users. We could divide the `userStream` Stream into two
   * separate Streams -- one for registered users, and one for unregistered users -- by doing the following:
   *
   * ```java
   * Stream userStream = ...
   *
   * Filter registeredFilter = new ResisteredUserFilter();
   * Filter unregisteredFilter = new Negate(registeredFilter);
   *
   * Stream registeredUserStream = userStream.each(userStream.getOutputFields(), registeredFilter);
   * Stream unregisteredUserStream = userStream.each(userStream.getOutputFields(), unregisteredFilter);
   * ```
   *
   */
  public class Negate implements Filter {
  
      Filter _delegate;
  
      public Negate(Filter delegate) {
          _delegate = delegate;
      }
  
      @Override
      public boolean isKeep(TridentTuple tuple) {
          return !_delegate.isKeep(tuple);
      }
  
      @Override
      public void prepare(Map conf, TridentOperationContext context) {
          _delegate.prepare(conf, context);
      }
  
      @Override
      public void cleanup() {
          _delegate.cleanup();
      }
  
  }
  