diff --git a/src/Main.java b/src/Main.java
index c21df79..2dce076 100644
--- a/src/Main.java
+++ b/src/Main.java
@@ -1,27 +1,14 @@
-import java.awt.BorderLayout;
-import java.awt.Container;
-import javax.swing.JComponent;
 import javax.swing.JFrame;
-import javax.swing.SwingUtilities;
 
 import frames.MainFrame;
-import panels.*;
 
 public class Main {
-	
+
 	// -------------------------------------------------------------------------
 	//
 	public static void main(String[] args) {
 
-		// -------------------------------------------------------------------------
-		//
-		SwingUtilities.invokeLater(new Runnable() {
-			public void run() {
-				
-				// generate window
-				JFrame mainFrame = new MainFrame();
-			}
-		});
-		// -------------------------------------------------------------------------
+		// generate window
+		JFrame mainFrame = new MainFrame();
 	}
 }
diff --git a/src/frames/MainFrame.java b/src/frames/MainFrame.java
index 485a2a0..56a61cb 100644
--- a/src/frames/MainFrame.java
+++ b/src/frames/MainFrame.java
@@ -1,28 +1,21 @@
 package frames;
 
 import java.awt.BorderLayout;
-import java.util.HashMap;
 
 import javax.swing.JFrame;
 import javax.swing.JPanel;
 
-import panels.*;
-import resources.Customer;
+import panels.MainPanel;
+import panels.ShowHistoryPanel;
 import resources.CustomersModel;
 
 //-------------------------------------------------------------------------
 // 
 public class MainFrame extends JFrame implements IMainFrame {
-
-	// field
-	private State state;
 	
 	// model
 	private CustomersModel model;
 
-	// panel
-	private JPanel curPanel;
-
 	// cache
 	private MainPanel mainPanel;
 	private ShowHistoryPanel historyPanel;
diff --git a/src/panels/MainPanel.java b/src/panels/MainPanel.java
index c2e566c..862a32a 100644
--- a/src/panels/MainPanel.java
+++ b/src/panels/MainPanel.java
@@ -5,24 +5,14 @@
 import java.awt.FlowLayout;
 import java.awt.event.ActionEvent;
 import java.awt.event.ActionListener;
-import java.util.EventListener;
-import java.util.HashMap;
-import java.util.Random;
 
-import javax.swing.DefaultListModel;
 import javax.swing.JButton;
-import javax.swing.JList;
 import javax.swing.JPanel;
 import javax.swing.JScrollPane;
 import javax.swing.JTable;
-import javax.swing.JTextField;
-import javax.swing.event.TableModelEvent;
 import javax.swing.table.DefaultTableModel;
-import javax.swing.table.TableModel;
 
 import frames.IMainFrame;
-import frames.MainFrame;
-import frames.State;
 import resources.Customer;
 import resources.CustomersModel;
 
@@ -44,7 +34,7 @@
 	// buttons
 	private JButton addButton;
 	private JButton removeButton;
-	private JButton showDetailButton;
+	private JButton showHistoryButton;
 
 	// -------------------------------------------------------------------------
 	// -------------------------------------------------------------------------
@@ -71,22 +61,22 @@
 		// add buttons
 		addButton = new JButton("Add");
 		removeButton = new JButton("Remove");
-		showDetailButton = new JButton("Show History");
+		showHistoryButton = new JButton("Show History");
 
 		// add listener
 		addButton.addActionListener(new AddActionHandler());
 		removeButton.addActionListener(new RemoveActionHandler());
-		showDetailButton.addActionListener(new ShowHistoryActionHandler());
+		showHistoryButton.addActionListener(new ShowHistoryActionHandler());
 
 		JPanel buttonPanel = new JPanel();
 		buttonPanel.add(addButton, BorderLayout.WEST);
 		buttonPanel.add(removeButton, BorderLayout.EAST);
 		add(buttonPanel, BorderLayout.CENTER);
 
-		// add show detail
+		// add show history
 		JPanel showButtonPanel = new JPanel();
 		FlowLayout flowLayout = new FlowLayout();
-		showButtonPanel.add(showDetailButton, BorderLayout.SOUTH);
+		showButtonPanel.add(showHistoryButton, BorderLayout.SOUTH);
 		showButtonPanel.setLayout(flowLayout);
 		add(showButtonPanel, BorderLayout.SOUTH);
 
diff --git a/src/panels/ShowHistoryPanel.java b/src/panels/ShowHistoryPanel.java
index d365585..628fb45 100644
--- a/src/panels/ShowHistoryPanel.java
+++ b/src/panels/ShowHistoryPanel.java
@@ -53,7 +53,7 @@
 		this.model = model;
 
 		// initialize table
-		historiesListModel = new DefaultListModel();
+		historiesListModel = new DefaultListModel<Integer>();
 		historiesList = new JList(historiesListModel);
 
 		BoxLayout layout = new BoxLayout(this, BoxLayout.Y_AXIS);
@@ -81,8 +81,8 @@
 		panel.add(payButton);
 		panel.add(backButton);
 
-		add(panel);
-		add(backButton);
+		this.add(panel);
+		this.add(backButton);
 
 		// add listener
 		backButton.addActionListener(new BackActionHandler());
@@ -95,11 +95,11 @@
 	// public
 	// -------------------------------------------------------------------------
 	//
-	public void updateListModelByIndex(int index) {
-		selectedCustomer = model.getCustomers().get(index);
+	public void updateListModelByIndex(int customerId) {
+		selectedCustomer = model.getCustomers().get(customerId);
 
 		historiesListModel.removeAllElements();
-		historiesListModel.addAll(model.getCustomers().get(index).getHistory());
+		historiesListModel.addAll(model.getCustomers().get(customerId).getHistory());
 
 		nameLabel.setText("name: " + selectedCustomer.getName());
 	}
@@ -130,6 +130,9 @@
 	// -------------------------------------------------------------------------
 	// payment button's event
 	private class PaymentActionHandler implements ActionListener {
+
+		// -------------------------------------------------------------------------
+		//
 		public void actionPerformed(ActionEvent e) {
 
 			String text = textField.getText();
diff --git a/src/resources/Customer.java b/src/resources/Customer.java
index 225b25d..70c0fdd 100644
--- a/src/resources/Customer.java
+++ b/src/resources/Customer.java
@@ -1,5 +1,6 @@
 package resources;
-import java.util.*;
+
+import java.util.List;
 
 //-------------------------------------------------------------------------
 // todo: add name field
@@ -9,31 +10,36 @@
 	private History history;
 	private Payment payment;
 	private String name; // added
-	public Customer(String name) {
+
+	public Customer(String name) { // added
 		points = new Points();
 		total = new Total();
 		history = new History(total);
-		payment = new Payment(points,history);
-		
-		// added
-		this.name = name;
+		payment = new Payment(points, history);
+
+		this.name = name; // added
 	}
+
 	public void purchase(int x) {
 		this.payment.purchase(x);
 	}
+
 	public int getTotal() {
 		return total.getValue();
 	}
+
 	public int getPayment() {
 		return payment.getValue();
 	}
+
 	public List<Integer> getHistory() {
 		return history.getValue();
 	}
+
 	public int getPoints() {
 		return points.getValue();
 	}
-	
+
 	// added
 	public String getName() {
 		return this.name;