kafka Maybe 源码
kafka Maybe 代码
文件路径：/streams/src/main/java/org/apache/kafka/streams/state/internals/Maybe.java
/*
* 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 org.apache.kafka.streams.state.internals;
import java.util.NoSuchElementException;
import java.util.Objects;
/**
* A container that may be empty, may contain null, or may contain a value.
* Distinct from {@link java.util.Optional<T>}, since Optional cannot contain null.
*
* @param <T>
*/
public final class Maybe<T> {
private final T nullableValue;
private final boolean defined;
public static <T> Maybe<T> defined(final T nullableValue) {
return new Maybe<>(nullableValue);
}
public static <T> Maybe<T> undefined() {
return new Maybe<>();
}
private Maybe(final T nullableValue) {
this.nullableValue = nullableValue;
defined = true;
}
private Maybe() {
nullableValue = null;
defined = false;
}
public T getNullableValue() {
if (defined) {
return nullableValue;
} else {
throw new NoSuchElementException();
}
}
public boolean isDefined() {
return defined;
}
@Override
public boolean equals(final Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
final Maybe<?> maybe = (Maybe<?>) o;
// All undefined maybes are equal
// All defined null maybes are equal
return defined == maybe.defined &&
(!defined || Objects.equals(nullableValue, maybe.nullableValue));
}
@Override
public int hashCode() {
// Since all undefined maybes are equal, we can hard-code their hashCode to -1.
// Since all defined null maybes are equal, we can hard-code their hashCode to 0.
return defined ? nullableValue == null ? 0 : nullableValue.hashCode() : -1;
}
@Override
public String toString() {
if (defined) {
return "DefinedMaybe{" + nullableValue + "}";
} else {
return "UndefinedMaybe{}";
}
}
}
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