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

@@ -1,5 +1,6 @@
 package io.zipcoder;
 
+import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Iterator;
 
@@ -18,4 +19,5 @@ public abstract class Copier implements Runnable {
     }
 
     public abstract void run();
+
 }

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

@@ -1,6 +1,21 @@
 package io.zipcoder;
 
 public class MonkeyTypewriter {
+
+
+    /*
+    Unsafe threads work, but commented out for optimization.
+     */
+
+
+
+
+
+
+
+
+
+
     public static void main(String[] args) {
         String introduction = "It was the best of times,\n" +
                 "it was the blurst of times,\n" +
@@ -27,12 +42,30 @@ public class MonkeyTypewriter {
 
         // 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.
+        UnsafeCopier unsafeCopier0 = new UnsafeCopier(introduction);
+        SafeCopier safeCopier0 = new SafeCopier(introduction);
         try {
+//            new Thread(unsafeCopier0).start();
+//            new Thread(unsafeCopier0).start();
+//            new Thread(unsafeCopier0).start();
+//            new Thread(unsafeCopier0).start();
+//            new Thread(unsafeCopier0).start();
+
+            new Thread(safeCopier0).start();
+            new Thread(safeCopier0).start();
+            new Thread(safeCopier0).start();
+            new Thread(safeCopier0).start();
+            new Thread(safeCopier0).start();
+
+
+
             Thread.sleep(1000);
         } catch(InterruptedException e) {
             System.out.println("MAIN INTERRUPTED");
         }
 
+        System.out.println(safeCopier0.copied);
         // Print out the copied versions here.
     }
+
 }

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

@@ -1,8 +1,28 @@
 package io.zipcoder;
 
+import java.util.concurrent.locks.Lock;
+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.
  */
-public class SafeCopier {
+public class SafeCopier extends Copier {
+
+    public SafeCopier(String toCopy) {
+        super(toCopy);
+    }
+
+    public void run() {
+        Lock threadLock = new ReentrantLock();
+        while(stringIterator.hasNext() == true) {
+            threadLock.lock();
+
+            String w = stringIterator.next();
+            copied = copied + w + " ";
+
+            threadLock.unlock();
+        }
+
+    }
 }

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

@@ -5,10 +5,21 @@ package io.zipcoder;
  */
 public class UnsafeCopier extends Copier {
 
+    StringBuilder x = new StringBuilder();
+
     public UnsafeCopier(String toCopy) {
         super(toCopy);
     }
 
     public void run() {
+        while(stringIterator.hasNext() == true){
+            String w = stringIterator.next();
+            copied = copied + w + " ";
+
+            //    x.append(w + " ");
+            //System.out.println(copied);
+        }
+        }
+
+       // System.out.println(x.toString());
     }
-}