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BruceEckelBruceEckel
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Added "Constructors are not Thread-Safe"
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7 files changed

+135
-1
lines changed

7 files changed

+135
-1
lines changed

‎concurrent/GuardedIDField.java‎

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// concurrent/GuardedIDField.java
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// (c)2017 MindView LLC: see Copyright.txt
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// We make no guarantees that this code is fit for any purpose.
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// Visit http://OnJava8.com for more book information.
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import java.util.concurrent.atomic.*;
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public class GuardedIDField implements HasID {
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private static AtomicInteger counter =
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new AtomicInteger();
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private int id = counter.getAndAdd(1);
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public int getID() { return id; }
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public static void main(String[] args) {
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IDChecker.test(GuardedIDField::new);
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}
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}
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/* Output:
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0
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*/

‎concurrent/HasID.java‎

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// concurrent/HasID.java
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// (c)2017 MindView LLC: see Copyright.txt
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// We make no guarantees that this code is fit for any purpose.
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// Visit http://OnJava8.com for more book information.
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public interface HasID {
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int getID();
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}

‎concurrent/IDChecker.java‎

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// concurrent/IDChecker.java
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// (c)2017 MindView LLC: see Copyright.txt
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// We make no guarantees that this code is fit for any purpose.
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// Visit http://OnJava8.com for more book information.
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import java.util.*;
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import java.util.function.*;
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import java.util.stream.*;
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import java.util.concurrent.*;
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import com.google.common.collect.Sets;
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public class IDChecker {
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public static int SIZE = 100_000;
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static class MakeObjects
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implements Supplier<List<Integer>> {
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private Supplier<HasID> gen;
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public MakeObjects(Supplier<HasID> gen) {
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this.gen = gen;
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}
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@Override
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public List<Integer> get() {
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return
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Stream.generate(gen)
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.limit(SIZE)
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.map(HasID::getID)
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.collect(Collectors.toList());
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}
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}
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public static void test(Supplier<HasID> gen) {
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CompletableFuture<List<Integer>>
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groupA = CompletableFuture
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.supplyAsync(new MakeObjects(gen)),
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groupB = CompletableFuture
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.supplyAsync(new MakeObjects(gen));
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groupA.thenAcceptBoth(groupB, (a, b) -> {
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System.out.println(
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Sets.intersection(
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Sets.newHashSet(a),
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Sets.newHashSet(b)).size());
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}).join();
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}
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}

‎concurrent/SharedConstructorArgument.java‎

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// concurrent/SharedConstructorArgument.java
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// (c)2017 MindView LLC: see Copyright.txt
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// We make no guarantees that this code is fit for any purpose.
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// Visit http://OnJava8.com for more book information.
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import java.util.concurrent.atomic.*;
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interface SharedArg {
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int get();
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}
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class Unsafe implements SharedArg {
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private int i = 0;
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public int get() { return i++; }
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}
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class Safe implements SharedArg {
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private static AtomicInteger counter =
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new AtomicInteger();
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public int get() {
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return counter.getAndAdd(1);
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}
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}
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class SharedUser implements HasID {
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private final int id;
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public SharedUser(SharedArg sa) {
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id = sa.get();
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}
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@Override
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public int getID() { return id; }
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}
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public class SharedConstructorArgument {
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public static void main(String[] args) {
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Unsafe us = new Unsafe();
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IDChecker.test(() -> new SharedUser(us));
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Safe sa = new Safe();
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IDChecker.test(() -> new SharedUser(sa));
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}
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}
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/* Output:
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47747
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0
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*/

‎concurrent/StaticIDField.java‎

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// concurrent/StaticIDField.java
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// (c)2017 MindView LLC: see Copyright.txt
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// We make no guarantees that this code is fit for any purpose.
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// Visit http://OnJava8.com for more book information.
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public class StaticIDField implements HasID {
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private static int counter = 0;
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private int id = counter++;
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public int getID() { return id; }
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}

‎concurrent/TestStaticIDField.java‎

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// concurrent/TestStaticIDField.java
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// (c)2017 MindView LLC: see Copyright.txt
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// We make no guarantees that this code is fit for any purpose.
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// Visit http://OnJava8.com for more book information.
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public class TestStaticIDField {
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public static void main(String[] args) {
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IDChecker.test(StaticIDField::new);
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}
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}
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/* Output:
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47643
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*/

‎gradle/subprojects.gradle‎

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@@ -67,7 +67,7 @@ project(':collections') {
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configure(subprojects - project(':onjava')) {
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dependencies {
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compile project(':onjava')
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compile 'com.google.guava:guava:21.0-rc2'
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compile 'com.google.guava:guava:21.0'
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compileOnly "org.openjdk.jmh:jmh-core:${jmh.jmhVersion}"
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}
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}

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