Finished

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

             System.out.println("MAIN INTERRUPTED");
         }
         // Print out the copied versions here.
+        System.out.println("UNSAFE\n");
         System.out.println(unsafeCopier.copied);
-
+        System.out.println("\nSAFE\n");
         System.out.println(safeCopier.copied);
     }
 }

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

 package io.zipcoder;
 
+import java.util.concurrent.locks.ReentrantLock;
+
 /**
  * Make this extend the Copier like `UnsafeCopier`, except use locks to make sure that the actual intro gets printed
  * correctly every time.  Make the run method thread safe.
         super(toCopy);
 
     }
+    ReentrantLock lock = new ReentrantLock();
+
 
     public void run() {
-        while (stringIterator.hasNext()){
+        lock.lock();
+        try{
+        while (stringIterator.hasNext()) {
             copied += stringIterator.next() + " ";
         }
+
+        }finally {
+            lock.unlock();
+        }
     }
 }