done

src/main/java/io/zipcoder/Copier.java

@@ -18,4 +18,6 @@ public abstract class Copier implements Runnable {
     }
 
     public abstract void run();
+
+
 }

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

@@ -24,15 +24,27 @@ public class MonkeyTypewriter {
         // For each Copier(one safe and one unsafe), create and start 5 monkeys copying the introduction to
         // A Tale Of Two Cities.
 
+        UnsafeCopier unsafe = new UnsafeCopier(introduction);
+        SafeCopier safe = new SafeCopier(introduction);
+
+        for (int i = 0; i < 5; i++){
+            new Thread(unsafe).start();
+            new Thread(safe).start();
+        }
+
 
         // This wait is here because main is still a thread and we want the main method to print the finished copies
         // after enough time has passed.
         try {
             Thread.sleep(1000);
+
         } catch(InterruptedException e) {
             System.out.println("MAIN INTERRUPTED");
         }
 
         // Print out the copied versions here.
+        System.out.println("UNSAFE COPIER:\n"+unsafe.copied);
+        System.out.println();
+        System.out.println("SAFE COPIER:\n"+safe.copied);
     }
 }

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

@@ -1,8 +1,37 @@
 package io.zipcoder;
 
+import java.util.concurrent.locks.ReadWriteLock;
+import java.util.concurrent.locks.ReentrantReadWriteLock;
+
 /**
  * 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.
  */
-public class SafeCopier {
-}
+public class SafeCopier extends Copier {
+
+    ReadWriteLock instanceOfReadWriteLock;
+
+
+    public SafeCopier(String toCopy) {
+        super(toCopy);
+        instanceOfReadWriteLock = new ReentrantReadWriteLock();
+    }
+
+    public void run() {
+
+        instanceOfReadWriteLock.writeLock().lock();
+        instanceOfReadWriteLock.readLock().lock();
+
+        try {
+            while (stringIterator.hasNext()) {
+                copied += stringIterator.next() + " ";
+            }
+
+        } finally {
+            instanceOfReadWriteLock.writeLock().unlock();
+            instanceOfReadWriteLock.readLock().unlock();
+        }
+
+    }
+
+}

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

@@ -10,5 +10,8 @@ public class UnsafeCopier extends Copier {
     }
 
     public void run() {
+        while (stringIterator.hasNext()) {
+            copied += stringIterator.next() + " ";
+        }
     }
 }