ImmutablePair.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.commons.lang3.tuple;
import java.util.Map;
import java.util.Objects;
/**
* An immutable pair consisting of two {@link Object} elements.
*
* <p>Although the implementation is immutable, there is no restriction on the objects
* that may be stored. If mutable objects are stored in the pair, then the pair
* itself effectively becomes mutable.</p>
*
* <p>#ThreadSafe# if both paired objects are thread-safe</p>
*
* @param <L> the left element type
* @param <R> the right element type
*
* @since 3.0
*/
public class ImmutablePair<L, R> extends Pair<L, R> {
/**
* An empty array.
* <p>
* Consider using {@link #emptyArray()} to avoid generics warnings.
* </p>
*
* @since 3.10.
*/
public static final ImmutablePair<?, ?>[] EMPTY_ARRAY = {};
/**
* An immutable pair of nulls.
*/
// This is not defined with generics to avoid warnings in call sites.
@SuppressWarnings("rawtypes")
private static final ImmutablePair NULL = new ImmutablePair<>(null, null);
/** Serialization version */
private static final long serialVersionUID = 4954918890077093841L;
/**
* Returns the empty array singleton that can be assigned without compiler warning.
*
* @param <L> the left element type
* @param <R> the right element type
* @return the empty array singleton that can be assigned without compiler warning.
*
* @since 3.10.
*/
@SuppressWarnings("unchecked")
public static <L, R> ImmutablePair<L, R>[] emptyArray() {
return (ImmutablePair<L, R>[]) EMPTY_ARRAY;
}
/**
* Creates an immutable pair of two objects inferring the generic types.
*
* <p>This factory allows the pair to be created using inference to
* obtain the generic types.</p>
*
* @param <L> the left element type
* @param <R> the right element type
* @param left the left element, may be null
* @return a pair formed from the two parameters, not null
* @since 3.11
*/
public static <L, R> Pair<L, R> left(final L left) {
return ImmutablePair.of(left, null);
}
/**
* Returns an immutable pair of nulls.
*
* @param <L> the left element of this pair. Value is {@code null}.
* @param <R> the right element of this pair. Value is {@code null}.
* @return an immutable pair of nulls.
* @since 3.6
*/
@SuppressWarnings("unchecked")
public static <L, R> ImmutablePair<L, R> nullPair() {
return NULL;
}
/**
* Creates an immutable pair of two objects inferring the generic types.
*
* <p>This factory allows the pair to be created using inference to
* obtain the generic types.</p>
*
* @param <L> the left element type
* @param <R> the right element type
* @param left the left element, may be null
* @param right the right element, may be null
* @return a pair formed from the two parameters, not null
*/
public static <L, R> ImmutablePair<L, R> of(final L left, final R right) {
return left != null || right != null ? new ImmutablePair<>(left, right) : nullPair();
}
/**
* Creates an immutable pair from a map entry.
*
* <p>This factory allows the pair to be created using inference to
* obtain the generic types.</p>
*
* @param <L> the left element type
* @param <R> the right element type
* @param pair the existing map entry.
* @return a pair formed from the map entry
* @since 3.10
*/
public static <L, R> ImmutablePair<L, R> of(final Map.Entry<L, R> pair) {
return pair != null ? new ImmutablePair<>(pair.getKey(), pair.getValue()) : nullPair();
}
/**
* Creates an immutable pair of two non-null objects inferring the generic types.
*
* <p>This factory allows the pair to be created using inference to
* obtain the generic types.</p>
*
* @param <L> the left element type
* @param <R> the right element type
* @param left the left element, may not be null
* @param right the right element, may not be null
* @return a pair formed from the two parameters, not null
* @throws NullPointerException if any input is null
* @since 3.13.0
*/
public static <L, R> ImmutablePair<L, R> ofNonNull(final L left, final R right) {
return of(Objects.requireNonNull(left, "left"), Objects.requireNonNull(right, "right"));
}
/**
* Creates an immutable pair of two objects inferring the generic types.
*
* <p>This factory allows the pair to be created using inference to
* obtain the generic types.</p>
*
* @param <L> the left element type
* @param <R> the right element type
* @param right the right element, may be null
* @return a pair formed from the two parameters, not null
* @since 3.11
*/
public static <L, R> Pair<L, R> right(final R right) {
return ImmutablePair.of(null, right);
}
/** Left object */
public final L left;
/** Right object */
public final R right;
/**
* Create a new pair instance.
*
* @param left the left value, may be null
* @param right the right value, may be null
*/
public ImmutablePair(final L left, final R right) {
this.left = left;
this.right = right;
}
/**
* {@inheritDoc}
*/
@Override
public L getLeft() {
return left;
}
/**
* {@inheritDoc}
*/
@Override
public R getRight() {
return right;
}
/**
* Throws {@link UnsupportedOperationException}.
*
* <p>This pair is immutable, so this operation is not supported.</p>
*
* @param value the value to set
* @return never
* @throws UnsupportedOperationException as this operation is not supported
*/
@Override
public R setValue(final R value) {
throw new UnsupportedOperationException();
}
}