EmptyCollectionSerialization.java

/*
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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * This code is free software; you can redistribute it and/or modify it
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 *
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 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
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 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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/*
 * @test
 * @bug     4684279 7129185
 * @summary Empty utility collections should be singletons
 * @author  Josh Bloch
 * @run testng EmptyCollectionSerialization
 */

import java.util.*;
import java.util.function.Supplier;
import java.io.*;
import org.testng.annotations.Test;
import org.testng.annotations.DataProvider;

import static org.testng.Assert.fail;
import static org.testng.Assert.assertSame;

public class EmptyCollectionSerialization {
    private static Object patheticDeepCopy(Object o) throws Exception {
        // Serialize
        ByteArrayOutputStream bos = new ByteArrayOutputStream();
        ObjectOutputStream oos = new ObjectOutputStream(bos);
        oos.writeObject(o);
        byte[] serializedForm = bos.toByteArray();

        // Deserialize
        InputStream is = new ByteArrayInputStream(serializedForm);
        ObjectInputStream ois = new ObjectInputStream(is);
        return ois.readObject();
    }

    @Test(dataProvider="SerializableSingletons")
    public static void serializableSingletons(String description, Supplier<Object> o) {
        try {
            Object singleton = o.get();
            assertSame(o.get(), singleton, description + ": broken Supplier not returning singleton");
            Object copy = patheticDeepCopy(singleton);
            assertSame( copy, singleton, description + ": " +
                copy.getClass().getName() + "@" + Integer.toHexString(System.identityHashCode(copy)) +
                " is not the singleton " +
                singleton.getClass().getName() + "@" + Integer.toHexString(System.identityHashCode(singleton)));
        } catch(Exception all) {
            fail(description + ": Unexpected Exception", all);
        }
    }

    @DataProvider(name = "SerializableSingletons", parallel = true)
    public static Iterator<Object[]> navigableMapProvider() {
        return makeSingletons().iterator();
    }

    public static Collection<Object[]> makeSingletons() {
        return Arrays.asList(
            new Object[]{"Collections.EMPTY_LIST",
                (Supplier) () -> {return Collections.EMPTY_LIST;}},
            new Object[]{"Collections.EMPTY_MAP",
                (Supplier) () -> {return Collections.EMPTY_MAP;}},
            new Object[]{"Collections.EMPTY_SET",
                (Supplier) () -> {return Collections.EMPTY_SET;}},
            new Object[]{"Collections.singletonMap()",
                (Supplier) () -> {return Collections.emptyList();}},
            new Object[]{"Collections.emptyMap()",
                (Supplier) () -> {return Collections.emptyMap();}},
            new Object[]{"Collections.emptySet()",
                (Supplier) () -> {return Collections.emptySet();}},
            new Object[]{"Collections.emptySortedSet()",
                (Supplier) () -> {return Collections.emptySortedSet();}},
            new Object[]{"Collections.emptySortedMap()",
                (Supplier) () -> {return Collections.emptySortedMap();}},
            new Object[]{"Collections.emptyNavigableSet()",
                (Supplier) () -> {return Collections.emptyNavigableSet();}},
            new Object[]{"Collections.emptyNavigableMap()",
                (Supplier) () -> {return Collections.emptyNavigableMap();}}
            );
    }
}