Add toString() method

src/Customer.java

@@ -12,4 +12,9 @@ public class Customer {
 		
 		return this.id.equals(c.getId());
 	}
+	
+	@Override
+	public String toString() {
+		return id;
+	}
 }

src/Order.java

@@ -67,4 +67,10 @@ public abstract class Order {
 				&& this.c.equals(t.getCustomer()) && this.stock.equals(t.getStock())
 				&& this.qty == t.getQty() && this.price == t.getPrice();
 	}
+
+	@Override
+	public String toString() {
+		return "<" + time + "," + type + "," + c + "," + stock + "," + 
+					qty + "," + price + ">";
+	}
 }

src/Stock.java

@@ -12,4 +12,9 @@ public class Stock {
 		
 		return this.name.equals(s.getName());
 	}
+	
+	@Override
+	public String toString() {
+		return name;
+	}
 }