diff --git a/src/edu/temple/cis/c3238/banksim/Account.java b/src/edu/temple/cis/c3238/banksim/Account.java
index 4082223..2b87dd5 100644
--- a/src/edu/temple/cis/c3238/banksim/Account.java
+++ b/src/edu/temple/cis/c3238/banksim/Account.java
@@ -1,5 +1,8 @@
 package edu.temple.cis.c3238.banksim;
 
+import java.util.concurrent.locks.Lock;
+import java.util.concurrent.locks.ReentrantLock;
+
 /**
  * @author Cay Horstmann
  * @author Modified by Paul Wolfgang
@@ -10,21 +13,29 @@ public class Account {
     private volatile int balance;
     private final int id;
     private final Bank myBank;
-
+    
     public Account(Bank myBank, int id, int initialBalance) {
         this.myBank = myBank;
         this.id = id;
         balance = initialBalance;
     }
 
+    /* 
+     * getBalance() does not need to be synchronized, despite balance being
+     * a shared variable, because getBalance() does not modify balance. 
+     **/
     public int getBalance() {
         return balance;
     }
 
-    public boolean withdraw(int amount) {
+    /* 
+     * withdraw() method is synchronized via synchronized keyword in it's
+     * declaration 
+     **/
+    public synchronized boolean withdraw(int amount) {
         if (amount <= balance) {
             int currentBalance = balance;
-//            Thread.yield(); // Try to force collision
+            //Thread.yield(); // Try to force collision
             int newBalance = currentBalance - amount;
             balance = newBalance;
             return true;
@@ -33,15 +44,33 @@ public boolean withdraw(int amount) {
         }
     }
 
-    public void deposit(int amount) {
+    /* 
+     * synchronized same as withdraw()
+     **/
+    public synchronized void deposit(int amount) {
         int currentBalance = balance;
-//        Thread.yield();   // Try to force collision
+        //Thread.yield();   // Try to force collision
         int newBalance = currentBalance + amount;
         balance = newBalance;
+        
+        notifyAll();
+    }
+    
+    /*
+     * implementation of task 4
+     * this method waits for amount <= balance 
+     **/
+    public synchronized void waitForSufficientFunds(int amount) {
+        
+        while (myBank.isOpen() && amount >= balance) {
+            try {
+                wait();
+            } catch (InterruptedException ex) {/*ignore*/}
+        }
     }
     
     @Override
     public String toString() {
         return String.format("Account[%d] balance %d", id, balance);
     }
-}
+}
\ No newline at end of file
diff --git a/src/edu/temple/cis/c3238/banksim/Bank.java b/src/edu/temple/cis/c3238/banksim/Bank.java
index e419ba8..af4d22c 100644
--- a/src/edu/temple/cis/c3238/banksim/Bank.java
+++ b/src/edu/temple/cis/c3238/banksim/Bank.java
@@ -1,5 +1,6 @@
 package edu.temple.cis.c3238.banksim;
 
+import java.util.concurrent.locks.ReentrantLock;
 /**
  * @author Cay Horstmann
  * @author Modified by Paul Wolfgang
@@ -13,7 +14,10 @@ public class Bank {
     private long ntransacts = 0;
     private final int initialBalance;
     private final int numAccounts;
+    private final ReentrantLock rlock = new ReentrantLock();
 
+    private boolean open = true;
+    
     public Bank(int numAccounts, int initialBalance) {
         this.initialBalance = initialBalance;
         this.numAccounts = numAccounts;
@@ -25,20 +29,55 @@ public Bank(int numAccounts, int initialBalance) {
     }
 
     public void transfer(int from, int to, int amount) {
-//        accounts[from].waitForAvailableFunds(amount);
-        if (accounts[from].withdraw(amount)) {
-            accounts[to].deposit(amount);
+   
+        if (!open) {
+            return;
+        }
+        
+        /* waiting for amount <= balance via method call */
+        accounts[from].waitForSufficientFunds(amount);
+        
+        /* ReentrantLock used to manipulate account balances */
+        rlock.lock();
+        try {
+            if (accounts[from].withdraw(amount)) {
+                accounts[to].deposit(amount);
+            }
+        }
+        finally {
+            rlock.unlock();
+        }
+        
+        if (shouldTest()) {
+            test();
         }
-        if (shouldTest()) test();
-    }
+
+}
 
     public void test() {
+        
         int sum = 0;
-        for (Account account : accounts) {
-            System.out.printf("%s %s%n", 
+        
+        /*
+         * the shared part of this method is "account.getBalance"
+         * hence, we lock that part with a ReentrantLock
+         **/
+        rlock.lock();
+        
+        try {
+            
+            for (Account account : accounts) {
+                System.out.printf("%s %s%n", 
                     Thread.currentThread().toString(), account.toString());
-            sum += account.getBalance();
+                sum += account.getBalance();
+            }
+            
+        } 
+        
+        finally {
+            rlock.unlock();
         }
+        
         System.out.println(Thread.currentThread().toString() + 
                 " Sum: " + sum);
         if (sum != numAccounts * initialBalance) {
@@ -51,6 +90,7 @@ public void test() {
         }
     }
 
+    
     public int size() {
         return accounts.length;
     }
@@ -59,5 +99,27 @@ public int size() {
     public boolean shouldTest() {
         return ++ntransacts % NTEST == 0;
     }
+    
+    /* returns true when the account is open, false otherwise */    
+    public synchronized boolean isOpen() {
+        return open;
+    }
+    
+    /* method to satisfy Task 5; 
+     * closeBank() closes all accounts */
+    public void closeBank() {
+        
+        /* the open variable is shared and hence protected */
+        synchronized (this) {
+            open = false;
+        }
+        
+        /* wake up all waiting threads */
+        for (Account account : accounts) {
+            synchronized (account) {
+                account.notifyAll();
+            }
+        }
+    }
 
-}
+}
\ No newline at end of file
diff --git a/src/edu/temple/cis/c3238/banksim/BankSimMain.java b/src/edu/temple/cis/c3238/banksim/BankSimMain.java
index 7357332..04d8f89 100644
--- a/src/edu/temple/cis/c3238/banksim/BankSimMain.java
+++ b/src/edu/temple/cis/c3238/banksim/BankSimMain.java
@@ -18,10 +18,6 @@ public static void main(String[] args) {
             threads[i] = new TransferThread(b, i, INITIAL_BALANCE);
             threads[i].start();
         }
-
-//        b.test();
           System.out.printf("Bank transfer is in the process.\n");
     }
-}
-
-
+}
\ No newline at end of file
diff --git a/src/edu/temple/cis/c3238/banksim/TransferThread.java b/src/edu/temple/cis/c3238/banksim/TransferThread.java
index 7c9b8eb..37b0f38 100644
--- a/src/edu/temple/cis/c3238/banksim/TransferThread.java
+++ b/src/edu/temple/cis/c3238/banksim/TransferThread.java
@@ -23,5 +23,8 @@ public void run() {
             int amount = (int) (maxAmount * Math.random());
             bank.transfer(fromAccount, toAccount, amount);
         }
+        
+        /* when one bank closes, it calls closeBank (closing them all) */
+        bank.closeBank();
     }
 }