Good stuff

src/main/java/io/zipcoder/MonkeyTypewriter.java

@@ -76,6 +76,7 @@ public class MonkeyTypewriter {
 
         // Print out the copied versions here.
         unsafeOutput(unsafeCopier.copied);
+        System.out.println();
         safeOutput(safeCopier.copied);
     }
 

src/main/java/io/zipcoder/SafeCopier.java

@@ -9,18 +9,18 @@ import java.util.concurrent.locks.ReentrantLock;
  */
 public class SafeCopier extends Copier {
 
-    Lock sharedLock = new ReentrantLock();
-
     public SafeCopier(String toCopy) {
         super(toCopy);
     }
 
     public void run() {
-        sharedLock.lock();
-        if (stringIterator.hasNext()) {
-            copied += stringIterator.next() + " ";
+        while (stringIterator.hasNext()) {
+            synchronized (stringIterator) {
+                if (stringIterator.hasNext()) {
+                    copied += stringIterator.next() + " ";
+                }
+            }
         }
-        sharedLock.unlock();
     }
 
 }

src/main/java/io/zipcoder/UnsafeCopier.java

@@ -10,8 +10,10 @@ public class UnsafeCopier extends Copier {
     }
 
     public void run() {
-        if (stringIterator.hasNext()) {
-            copied += stringIterator.next() + " ";
+        while (stringIterator.hasNext()) {
+            if (stringIterator.hasNext()) {
+                copied += stringIterator.next() + " ";
+            }
         }
     }