Fully Tested and Commented Code

src/Order/Order.java

@@ -15,10 +15,22 @@ import javax.swing.plaf.synth.SynthSpinnerUI;
  */
 public class Order {
 			
+	String ord_ID;
+	String type;
+	String product;
+	String pro_ID;
+	int price;
+	int qty;
+	String cust_ID;
+	
+	
+	//Empty Constructor
 	public  Order()
 	{
 		
 	}
+	
+	//Copy Constructor
 	public Order(Order O)
 	{
 		super();
@@ -29,6 +41,8 @@ public class Order {
 		this.qty = O.qty;
 		this.cust_ID = O.cust_ID;
 	}
+	
+	//Constructor for Initialization
 	public Order(String ord_ID, String type, String product,  int price, int qty, String cust_ID) {
 		super();
 		this.ord_ID = ord_ID;
@@ -39,15 +53,6 @@ public class Order {
 		this.cust_ID = cust_ID;
 	}
 
-	String ord_ID;
-	String type;
-	String product;
-	String pro_ID;
-	int price;
-	int qty;
-	String cust_ID;
-	
-
 	public void read() {
 		Scanner s = new Scanner(System.in);
 		this.ord_ID = s.nextLine();

src/Order/OrderProcessing.java

@@ -2,12 +2,20 @@ package Order;
 
 import java.util.ArrayList;
 
+//Class for Processing the Orders 
 public class OrderProcessing {
+	
+	//OrderQueue in which all Orders are added and removed if they got a match.
 	private ArrayList<Order> orderQueue = new ArrayList<Order>();
 
+	//Processing Logic
 	public ArrayList<Order> Process( Order order) {
 		int lenth = orderQueue.size();
+		
+		//Matched Queue for storing the matched orders at that time only i.e. why i have declared locally so that it will persist for more than one orders.
 		ArrayList<Order> matched = new ArrayList<Order>();
+		
+		//if current order is sell type order
 		if ("Sell".equalsIgnoreCase(order.type)) {
 			int i = 0;
 			while (lenth-- > 0) {
@@ -29,7 +37,9 @@ public class OrderProcessing {
 					}
 				}
 			}
-		} else {
+		}
+		//if current order is buy type order 
+		else {
 			int i = 0;
 			while (lenth-- > 0) {
 				Order o = orderQueue.get(i++);
@@ -56,27 +66,33 @@ public class OrderProcessing {
 		return matched;
 	}
 
+	//getting the Current OrderQueue
 	public ArrayList<Order> getOrderQueue() {
 		return orderQueue;
 
 	}
-	public void pending(ArrayList<Order> matched) {
+	
+	//Function for pending orders
+	public void pending() {
 		// TODO Auto-generated method stub
 		for(int i=0;i<orderQueue.size();)
 		{
 			Order order = orderQueue.get(i);
 			if(order.qty != 0) 
 				{
+				//prints only non-zero quantity orders
 				System.out.println("Order #"+i++);
 				order.show();
 				}
 			else
 			{ 
+				//remove the zero quantity orders
 				orderQueue.remove(order);
 			}
 		}
 	}
 
+	//Function for returning matched orders
 	public void matched(ArrayList<Order> matched) {
 		// TODO Auto-generated method stub
 		for(int i=0;i<matched.size();i++)

src/main/Main.java

@@ -10,7 +10,7 @@ public class Main {
 
 	/**
 	 * @param args
-	 */
+	 *///Main Function
 	public static void main(String[] args) {
 		// TODO Auto-generated method stub
 		char choice = 'n';
@@ -18,17 +18,25 @@ public class Main {
 		OrderProcessing orderProcessing = new OrderProcessing();
 		do {
 			Order O1 = new Order();
+			
+			//Reading new order
 			System.out.println(
 					"Provide Order Details : \n [orderID : Type : Product : Price : Quantity : CustID]\n");
-			O1.read();  								 ///Reading new orders
-//			orders.add(O1);							//Added in the list                           
-			ArrayList<Order> matched = orderProcessing.Process(O1);								// Finding the match
+			O1.read();  
+			
 			
+			// Finding the match
+			ArrayList<Order> matched = orderProcessing.Process(O1);										
+			
+			// Producing the Matched Orders 
 			System.out.println("Matched Orders are : ");
 			orderProcessing.matched(matched);
+			
+			//Producing the Pending Orders
 			System.out.println("\nPending Orders till now are : ");
+			orderProcessing.pending();
 			
-			orderProcessing.pending(matched);								//Pending orders.
+			//Asking for New Orders 
 			System.out.println("\nWant to add new order : [y/n] \n ");
 			@SuppressWarnings("resource")
 			Scanner s = new Scanner(System.in);