/**
* 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();
}
}