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GitHub issue #30257
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Adds a static comparing method to the SerializableComparator interface
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kirupha2000 committed Aug 13, 2024
1 parent bf42a81 commit b0f2683
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import java.io.Serializable;
import java.util.Comparator;
import java.util.Objects;
import java.util.function.Function;

/**
* A {@code Comparator} that is also {@code Serializable}.
*
* @param <T> type of values being compared
*/
public interface SerializableComparator<T> extends Comparator<T>, Serializable {}
public interface SerializableComparator<T> extends Comparator<T>, Serializable {
/**
* Analogous to {@link Comparator#comparing(Function)}, except that it takes in a {@link
* SerializableFunction} as the key extractor and returns a {@link SerializableComparator}.
*
* @param keyExtractor the function used to extract the {@link java.lang.Comparable} sort key
* @return A {@link SerializableComparator} that compares by an extracted key
* @param <T> the type of element to be compared
* @param <V> the type of the {@code Comparable} sort key
* @see Comparator#comparing(Function)
*/
static <T, V extends Comparable<? super V>> SerializableComparator<T> comparing(
SerializableFunction<? super T, ? extends V> keyExtractor) {
Objects.requireNonNull(keyExtractor);
return (SerializableComparator<T>)
(c1, c2) -> keyExtractor.apply(c1).compareTo(keyExtractor.apply(c2));
}
}
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/*
* 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.beam.sdk.transforms;

import java.io.Serializable;
import java.util.function.Function;
import org.apache.beam.sdk.util.SerializableUtils;
import org.junit.Assert;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.junit.runners.JUnit4;

/** Tests for {@link SerializableComparator}. */
@RunWith(JUnit4.class)
public class SerializableComparatorTest {

/**
* Tests if the {@link SerializableComparator} returned by {@link
* SerializableComparator#comparing(SerializableFunction)} using {@link
* SerializableUtils#ensureSerializable(Serializable)}.
*/
@Test
public void testSerializable() {
SerializableFunction<String, Integer> fn = Integer::parseInt;

SerializableComparator<String> cmp = SerializableComparator.comparing(fn);
SerializableUtils.ensureSerializable(cmp);
}

/**
* Tests if {@link SerializableComparator#comparing(Function)} throws a {@link
* java.lang.NullPointerException} if <code>null</code> is passed to it.
*/
@Test(expected = NullPointerException.class)
public void testIfNPEThrownForNullFunction() {
SerializableComparator.comparing(null);
}

/** Tests the basic comparison function of the {@link SerializableComparator} returned. */
@Test
public void testBasicComparison() {
SerializableFunction<String, Integer> fn = Integer::parseInt;
SerializableComparator<String> cmp = SerializableComparator.comparing(fn);

Assert.assertTrue(cmp.compare("1", "10") < 0);
Assert.assertTrue(cmp.compare("9", "6") > 0);
}
}

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