diff --git a/concurrent/GuardedIDField.java b/concurrent/GuardedIDField.java
new file mode 100644
index 00000000..0ab48d2e
--- /dev/null
+++ b/concurrent/GuardedIDField.java
@@ -0,0 +1,18 @@
+// concurrent/GuardedIDField.java
+// (c)2017 MindView LLC: see Copyright.txt
+// We make no guarantees that this code is fit for any purpose.
+// Visit http://OnJava8.com for more book information.
+import java.util.concurrent.atomic.*;
+
+public class GuardedIDField implements HasID {
+  private static AtomicInteger counter =
+    new AtomicInteger();
+  private int id = counter.getAndAdd(1);
+  public int getID() { return id; }
+  public static void main(String[] args) {
+    IDChecker.test(GuardedIDField::new);
+  }
+}
+/* Output:
+0
+*/
diff --git a/concurrent/HasID.java b/concurrent/HasID.java
new file mode 100644
index 00000000..4e679a59
--- /dev/null
+++ b/concurrent/HasID.java
@@ -0,0 +1,8 @@
+// concurrent/HasID.java
+// (c)2017 MindView LLC: see Copyright.txt
+// We make no guarantees that this code is fit for any purpose.
+// Visit http://OnJava8.com for more book information.
+
+public interface HasID {
+  int getID();
+}
diff --git a/concurrent/IDChecker.java b/concurrent/IDChecker.java
new file mode 100644
index 00000000..e4f7cac5
--- /dev/null
+++ b/concurrent/IDChecker.java
@@ -0,0 +1,41 @@
+// concurrent/IDChecker.java
+// (c)2017 MindView LLC: see Copyright.txt
+// We make no guarantees that this code is fit for any purpose.
+// Visit http://OnJava8.com for more book information.
+import java.util.*;
+import java.util.function.*;
+import java.util.stream.*;
+import java.util.concurrent.*;
+import com.google.common.collect.Sets;
+
+public class IDChecker {
+  public static int SIZE = 100_000;
+  static class MakeObjects
+  implements Supplier<List<Integer>> {
+    private Supplier<HasID> gen;
+    public MakeObjects(Supplier<HasID> gen) {
+      this.gen = gen;
+    }
+    @Override
+    public List<Integer> get() {
+      return
+        Stream.generate(gen)
+          .limit(SIZE)
+          .map(HasID::getID)
+          .collect(Collectors.toList());
+    }
+  }
+  public static void test(Supplier<HasID> gen) {
+    CompletableFuture<List<Integer>>
+      groupA = CompletableFuture
+        .supplyAsync(new MakeObjects(gen)),
+      groupB = CompletableFuture
+        .supplyAsync(new MakeObjects(gen));
+    groupA.thenAcceptBoth(groupB, (a, b) -> {
+      System.out.println(
+        Sets.intersection(
+          Sets.newHashSet(a),
+          Sets.newHashSet(b)).size());
+    }).join();
+  }
+}
diff --git a/concurrent/SharedConstructorArgument.java b/concurrent/SharedConstructorArgument.java
new file mode 100644
index 00000000..0cf835d8
--- /dev/null
+++ b/concurrent/SharedConstructorArgument.java
@@ -0,0 +1,44 @@
+// concurrent/SharedConstructorArgument.java
+// (c)2017 MindView LLC: see Copyright.txt
+// We make no guarantees that this code is fit for any purpose.
+// Visit http://OnJava8.com for more book information.
+import java.util.concurrent.atomic.*;
+
+interface SharedArg {
+  int get();
+}
+
+class Unsafe implements SharedArg {
+  private int i = 0;
+  public int get() { return i++; }
+}
+
+class Safe implements SharedArg {
+  private static AtomicInteger counter =
+    new AtomicInteger();
+  public int get() {
+    return counter.getAndAdd(1);
+  }
+}
+
+class SharedUser implements HasID {
+  private final int id;
+  public SharedUser(SharedArg sa) {
+    id = sa.get();
+  }
+  @Override
+  public int getID() { return id; }
+}
+
+public class SharedConstructorArgument {
+  public static void main(String[] args) {
+    Unsafe us = new Unsafe();
+    IDChecker.test(() -> new SharedUser(us));
+    Safe sa = new Safe();
+    IDChecker.test(() -> new SharedUser(sa));
+  }
+}
+/* Output:
+47747
+0
+*/
diff --git a/concurrent/StaticIDField.java b/concurrent/StaticIDField.java
new file mode 100644
index 00000000..9e563dfd
--- /dev/null
+++ b/concurrent/StaticIDField.java
@@ -0,0 +1,10 @@
+// concurrent/StaticIDField.java
+// (c)2017 MindView LLC: see Copyright.txt
+// We make no guarantees that this code is fit for any purpose.
+// Visit http://OnJava8.com for more book information.
+
+public class StaticIDField implements HasID {
+  private static int counter = 0;
+  private int id = counter++;
+  public int getID() { return id; }
+}
diff --git a/concurrent/TestStaticIDField.java b/concurrent/TestStaticIDField.java
new file mode 100644
index 00000000..5ad53adb
--- /dev/null
+++ b/concurrent/TestStaticIDField.java
@@ -0,0 +1,13 @@
+// concurrent/TestStaticIDField.java
+// (c)2017 MindView LLC: see Copyright.txt
+// We make no guarantees that this code is fit for any purpose.
+// Visit http://OnJava8.com for more book information.
+
+public class TestStaticIDField {
+  public static void main(String[] args) {
+    IDChecker.test(StaticIDField::new);
+  }
+}
+/* Output:
+47643
+*/
diff --git a/gradle/subprojects.gradle b/gradle/subprojects.gradle
index d22a7cff..e114237d 100644
--- a/gradle/subprojects.gradle
+++ b/gradle/subprojects.gradle
@@ -67,7 +67,7 @@ project(':collections') {
 configure(subprojects - project(':onjava')) {
     dependencies {
         compile project(':onjava')
-        compile 'com.google.guava:guava:21.0-rc2'
+        compile 'com.google.guava:guava:21.0'
         compileOnly "org.openjdk.jmh:jmh-core:${jmh.jmhVersion}"
     }
 }