done

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

@@ -23,12 +23,32 @@ public class MonkeyTypewriter {
         // Do all of the Monkey / Thread building here
         // For each Copier(one safe and one unsafe), create and start 5 monkeys copying the introduction to
         // A Tale Of Two Cities.
+        UnsafeCopier unsafeCopier=new UnsafeCopier(introduction);
+        for(int i=0;i<5;i++)
+        {
+
+            Thread thread=new Thread(unsafeCopier);
+            thread.start();
+
+        }
+
+        SafeCopier safeCopier=new SafeCopier(introduction);
+        for(int i=0;i<5;i++)
+        {
+
+            Thread thread=new Thread(safeCopier);
+            thread.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);
+            System.out.println("Unsafe"+unsafeCopier.copied);
+            System.out.println("Safe"+safeCopier.copied);
         } catch(InterruptedException e) {
             System.out.println("MAIN INTERRUPTED");
         }

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

@@ -3,6 +3,24 @@ package io.zipcoder;
 /**
  * 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.
+ * https://www.journaldev.com/2377/java-lock-example-reentrantlock
  */
-public class SafeCopier {
+
+import java.util.*;
+import java.util.concurrent.locks.Lock;
+import java.util.concurrent.locks.ReentrantLock;
+
+public class SafeCopier  extends Copier{
+    public SafeCopier(String toCopy) {
+        super(toCopy);
+    }
+    private Lock lock=new ReentrantLock();
+    public void run() {
+        lock.lock();
+        while(stringIterator.hasNext())
+        {
+            copied=copied+stringIterator.next();
+        }
+        lock.unlock();
+    }
 }

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

@@ -10,5 +10,9 @@ public class UnsafeCopier extends Copier {
     }
 
     public void run() {
+        while(stringIterator.hasNext())
+        {
+            copied=copied+stringIterator.next();
+        }
     }
 }