com.hazelcast.jet.core.ResettableSingletonTraverser Maven / Gradle / Ivy
/*
* Copyright (c) 2008-2024, 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.core;
import com.hazelcast.jet.Traverser;
import javax.annotation.Nullable;
import java.util.function.Consumer;
/**
* Traverses over a single item which can be set from the outside, by using
* this traverser as a {@code Consumer}. Another item can be set at any
* time and the subsequent {@code next()} call will consume it. However,
* if this traverser already has an item, it is illegal to set another one
* before consuming it.
*
* See {@link AppendableTraverser} if you have more items to traverse.
* @param item type
*
* @since Jet 3.0
*/
public class ResettableSingletonTraverser implements Traverser, Consumer {
private T item;
@Override
public T next() {
try {
return item;
} finally {
item = null;
}
}
/**
* Resets this traverser so that the following {@code next()} call will
* return the item supplied here. If the traverser already has an item, it
* is illegal to call this method until that item is consumed by calling
* {@link #next()}.
*
* @param item the item to return from {@code next()}
*/
@Override
public void accept(@Nullable T item) {
assert this.item == null :
"accept() called, but previous item still present. Previous: " + this.item + ", new: " + item;
this.item = item;
}
}