com.hazelcast.jet.function.DistributedFunctions Maven / Gradle / Ivy
/*
* Copyright (c) 2008-2018, Hazelcast, Inc. All Rights Reserved.
*
* 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 com.hazelcast.jet.function;
import javax.annotation.Nonnull;
import java.util.Map;
import java.util.Map.Entry;
/**
* Factory methods for several common distributed functions.
*/
public final class DistributedFunctions {
/**
* The string key returned by {@link #constantKey()}.
*/
public static final String CONSTANT_KEY = "ALL";
private DistributedFunctions() {
}
/**
* Synonym for {@link DistributedFunction#identity}, to be used as a
* projection function (e.g., key extractor).
*/
@Nonnull
public static DistributedFunction wholeItem() {
return DistributedFunction.identity();
}
/**
* Returns a function that extracts the key of a {@link Map.Entry}.
*
* @param type of entry's key
*/
@Nonnull
public static DistributedFunction, K> entryKey() {
return Map.Entry::getKey;
}
/**
* Returns a function that extracts the value of a {@link Map.Entry}.
*
* @param type of entry's value
*/
@Nonnull
public static DistributedFunction, V> entryValue() {
return Map.Entry::getValue;
}
/**
* Returns a function that always evaluates to the {@link #CONSTANT_KEY}.
* This is useful as a key extractor in group-by operations where no
* classification by key is desired.
*/
@Nonnull
public static DistributedFunction constantKey() {
return t -> CONSTANT_KEY;
}
/**
* Returns a consumer that does nothing with the argument.
*/
@Nonnull
public static DistributedConsumer noopConsumer() {
return t -> {
};
}
/**
* Returns a predicate that always evaluates to {@code true}.
*/
@Nonnull
public static DistributedPredicate alwaysTrue() {
return t -> true;
}
/**
* Return sa predicate that always evaluates to {@code false}.
*/
@Nonnull
public static DistributedPredicate alwaysFalse() {
return t -> false;
}
}