org.apache.spark.api.java.Optional Maven / Gradle / Ivy
/*
* 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.spark.api.java;
import java.io.Serializable;
import java.util.Objects;
import com.google.common.base.Preconditions;
/**
* Like {@code java.util.Optional} in Java 8, {@code scala.Option} in Scala, and
* {@code com.google.common.base.Optional} in Google Guava, this class represents a
* value of a given type that may or may not exist. It is used in methods that wish
* to optionally return a value, in preference to returning {@code null}.
*
* In fact, the class here is a reimplementation of the essential API of both
* {@code java.util.Optional} and {@code com.google.common.base.Optional}. From
* {@code java.util.Optional}, it implements:
*
*
* - {@link #empty()}
* - {@link #of(Object)}
* - {@link #ofNullable(Object)}
* - {@link #get()}
* - {@link #orElse(Object)}
* - {@link #isPresent()}
*
*
* From {@code com.google.common.base.Optional} it implements:
*
*
* - {@link #absent()}
* - {@link #of(Object)}
* - {@link #fromNullable(Object)}
* - {@link #get()}
* - {@link #or(Object)}
* - {@link #orNull()}
* - {@link #isPresent()}
*
*
* {@code java.util.Optional} itself was not used because at the time, the
* project did not require Java 8. Using {@code com.google.common.base.Optional}
* has in the past caused serious library version conflicts with Guava that can't
* be resolved by shading. Hence this work-alike clone.
*
* @param type of value held inside
*/
public final class Optional implements Serializable {
private static final Optional EMPTY = new Optional<>();
private final T value;
private Optional() {
this.value = null;
}
private Optional(T value) {
Preconditions.checkNotNull(value);
this.value = value;
}
// java.util.Optional API (subset)
/**
* @return an empty {@code Optional}
*/
public static Optional empty() {
@SuppressWarnings("unchecked")
Optional t = (Optional) EMPTY;
return t;
}
/**
* @param value non-null value to wrap
* @return {@code Optional} wrapping this value
* @throws NullPointerException if value is null
*/
public static Optional of(T value) {
return new Optional<>(value);
}
/**
* @param value value to wrap, which may be null
* @return {@code Optional} wrapping this value, which may be empty
*/
public static Optional ofNullable(T value) {
if (value == null) {
return empty();
} else {
return of(value);
}
}
/**
* @return the value wrapped by this {@code Optional}
* @throws NullPointerException if this is empty (contains no value)
*/
public T get() {
Preconditions.checkNotNull(value);
return value;
}
/**
* @param other value to return if this is empty
* @return this {@code Optional}'s value if present, or else the given value
*/
public T orElse(T other) {
return value != null ? value : other;
}
/**
* @return true iff this {@code Optional} contains a value (non-empty)
*/
public boolean isPresent() {
return value != null;
}
// Guava API (subset)
// of(), get() and isPresent() are identically present in the Guava API
/**
* @return an empty {@code Optional}
*/
public static Optional absent() {
return empty();
}
/**
* @param value value to wrap, which may be null
* @return {@code Optional} wrapping this value, which may be empty
*/
public static Optional fromNullable(T value) {
return ofNullable(value);
}
/**
* @param other value to return if this is empty
* @return this {@code Optional}'s value if present, or else the given value
*/
public T or(T other) {
return value != null ? value : other;
}
/**
* @return this {@code Optional}'s value if present, or else null
*/
public T orNull() {
return value;
}
// Common methods
@Override
public boolean equals(Object obj) {
if (!(obj instanceof Optional)) {
return false;
}
Optional other = (Optional) obj;
return Objects.equals(value, other.value);
}
@Override
public int hashCode() {
return value == null ? 0 : value.hashCode();
}
@Override
public String toString() {
return value == null ? "Optional.empty" : String.format("Optional[%s]", value);
}
}