diff --git a/me/smartstore/Main.java b/me/smartstore/Main.java
new file mode 100644
index 00000000..291f0fa5
--- /dev/null
+++ b/me/smartstore/Main.java
@@ -0,0 +1,8 @@
+package me.smartstore;
+
+public class Main {
+    public static void main(String[] args) {
+        SmartStoreApp.getInstance().test().run(); // function chaining
+//        SmartStoreApp.getInstance().run();
+    }
+}
diff --git a/me/smartstore/SmartStoreApp.java b/me/smartstore/SmartStoreApp.java
new file mode 100644
index 00000000..c8ddd316
--- /dev/null
+++ b/me/smartstore/SmartStoreApp.java
@@ -0,0 +1,64 @@
+package me.smartstore;
+
+
+import me.smartstore.customer.Customer;
+import me.smartstore.customer.Customers;
+import me.smartstore.group.Group;
+import me.smartstore.group.GroupType;
+import me.smartstore.group.Groups;
+import me.smartstore.group.Parameter;
+import me.smartstore.menu.MainMenu;
+
+public class SmartStoreApp {
+    private final Groups allGroups = Groups.getInstance();
+    private final Customers allCustomers = Customers.getInstance();
+
+    private final MainMenu mainMenu = MainMenu.getInstance();
+
+    // singleton
+    private static SmartStoreApp smartStoreApp;
+
+    public static SmartStoreApp getInstance() {
+        if (smartStoreApp == null) {
+            smartStoreApp = new SmartStoreApp();
+        }
+        return smartStoreApp;
+    }
+
+    private SmartStoreApp() {}
+
+    public void details() {
+        System.out.println("\n\n===========================================");
+        System.out.println(" Title : SmartStore Customer Classification");
+        System.out.println(" Release Date : 23.05.09");
+        System.out.println(" Copyright 2023 Inyoung All rights reserved.");
+        System.out.println("===========================================\n");
+    }
+
+    public SmartStoreApp test() {
+        allGroups.add(new Group(new Parameter(10, 100000), GroupType.GENERAL));
+        allGroups.add(new Group(new Parameter(20, 200000), GroupType.VIP));
+        allGroups.add(new Group(new Parameter(30, 300000), GroupType.VVIP));
+
+        for (int i = 0; i < 26; i++) {
+            allCustomers.add(new Customer(
+                    Character.toString((char) ('a' + i)),
+                    (char) ('a' + i) + "123",
+                    ((int) (Math.random() * 5) + 1) * 10,
+                    ((int) (Math.random() * 5) + 1) * 100000));
+        }
+
+        System.out.println("allCustomers = " + allCustomers);
+        System.out.println("allGroups = " + allGroups);
+
+        allCustomers.refresh(allGroups);
+
+        return this;
+    }
+
+    public void run() {
+        details();
+        mainMenu.manage();
+
+    }
+}
diff --git a/me/smartstore/arrays/Collections.java b/me/smartstore/arrays/Collections.java
new file mode 100644
index 00000000..8f6564cc
--- /dev/null
+++ b/me/smartstore/arrays/Collections.java
@@ -0,0 +1,15 @@
+package me.smartstore.arrays;
+
+
+public interface Collections<T> {
+
+    int size();
+    T get(int index);
+    void set(int index, T object);
+    int indexOf(T object);
+    void add(T object);
+    void add(int index, T object);
+    T pop();
+    T pop(int index);
+    T pop(T object);
+}
\ No newline at end of file
diff --git a/me/smartstore/arrays/DArray.java b/me/smartstore/arrays/DArray.java
new file mode 100644
index 00000000..6b273986
--- /dev/null
+++ b/me/smartstore/arrays/DArray.java
@@ -0,0 +1,140 @@
+package me.smartstore.arrays;
+
+import me.smartstore.exception.ElementNotFoundException;
+import me.smartstore.exception.EmptyArrayException;
+import me.smartstore.exception.NullArgumentException;
+
+public class DArray<T> implements Collections<T> {
+
+    protected static final int DEFAULT = 10;
+
+    protected T[] arrays;
+    protected int size;
+    protected int capacity;
+
+    @SuppressWarnings("unchecked")
+    public DArray() {
+        arrays = (T[]) new Object[DEFAULT];
+        capacity = DEFAULT;
+    }
+
+    @SuppressWarnings("unchecked")
+    public DArray(int initial) {
+        arrays = (T[]) new Object[initial];
+        capacity = initial;
+    }
+
+    public DArray(T[] arrays) {
+        this.arrays = arrays;
+        capacity = arrays.length;
+        size = arrays.length;
+    }
+
+    @Override
+    public int size() {
+        return size;
+    }
+
+    // 배열에 얼마나 capacity 남아있는지 외부에 알려줄 필요가 없기 때문에 <protected>으로 정의
+    protected int capacity() {
+        return capacity;
+    }
+
+    @Override
+    public T get(int index) throws IndexOutOfBoundsException {
+        if (index < 0 || index >= size) throw new IndexOutOfBoundsException();
+        return arrays[index];
+    }
+
+
+    @Override
+    public void set(int index, T object) throws IndexOutOfBoundsException, NullArgumentException {
+        if (index < 0 || index >= size) throw new IndexOutOfBoundsException();
+        if (object == null) throw new NullArgumentException();
+
+        arrays[index] = object;
+    }
+
+    @Override
+    public int indexOf(T object) throws NullArgumentException, ElementNotFoundException {
+        if (object == null) throw new NullArgumentException(); // not found (instead of throwing exception)
+
+        for (int i = 0; i < size; i++) {
+            if (arrays[i] == null) continue;
+            if (arrays[i].equals(object)) return i;
+        }
+        throw new ElementNotFoundException(); // not found
+    }
+
+    @Override
+    public void add(T object) throws NullArgumentException {
+        if (object == null) throw new NullArgumentException(); // if argument is null, do not add null value in array
+
+        if (size < capacity) {
+            arrays[size] = object;
+            size++;
+        } else {
+            grow();
+            add(object);
+        }
+    }
+
+    @Override
+    public void add(int index, T object) throws IndexOutOfBoundsException, NullArgumentException {
+        if (index < 0 || index >= size) throw new IndexOutOfBoundsException();
+        if (object == null) throw new NullArgumentException();
+
+        if (size < capacity) {
+            for (int i = size-1; i >= index ; i--) {
+                arrays[i+1] = arrays[i];
+            }
+            arrays[index] = object;
+            size++;
+        } else {
+            grow();
+            add(index, object);
+        }
+    }
+
+    @Override
+    public T pop() {
+        return pop(size-1);
+    }
+
+    @Override
+    public T pop(int index) throws IndexOutOfBoundsException {
+        if (size == 0) throw new EmptyArrayException();
+        if (index < 0 || index >= size) throw new IndexOutOfBoundsException();
+
+        T popElement = arrays[index];
+        arrays[index] = null; // 삭제됨을 명시적으로 표현
+
+        for (int i = index+1; i < size; i++) {
+            arrays[i-1] = arrays[i];
+        }
+        arrays[size-1] = null;
+        size--;
+        return popElement;
+    }
+
+    @Override
+    public T pop(T object) {
+        return pop(indexOf(object));
+    }
+
+    protected void grow() {
+        capacity *= 2; // doubling
+        arrays = java.util.Arrays.copyOf(arrays, capacity);
+
+        // size는 그대로
+    }
+
+    @Override
+    public String toString() {
+        String toStr = "";
+        for (int i = 0; i < size; i++) {
+            toStr += (arrays[i] + "\n");
+        }
+        return toStr;
+    }
+}
diff --git a/me/smartstore/customer/Customer.java b/me/smartstore/customer/Customer.java
new file mode 100644
index 00000000..87d0ba12
--- /dev/null
+++ b/me/smartstore/customer/Customer.java
@@ -0,0 +1,100 @@
+package me.smartstore.customer;
+
+import me.smartstore.group.Group;
+
+import java.util.Objects;
+
+public class Customer implements Comparable<Customer>{
+    private String cusName;
+    private String cusId;
+    private Integer cusTotalTime;
+    private Integer cusTotalPay;
+    private Group group; // 현재 분류 기준에 의해 각 고객을 분류된 결과
+
+    public Customer() {
+    }
+
+    public Customer(String cusId) {
+        this.cusId = cusId;
+    }
+
+    public Customer(String cusName, String cusId) {
+        this.cusName = cusName;
+        this.cusId = cusId;
+    }
+
+    public Customer(String cusName, String cusId, Integer cusTotalTime, Integer cusTotalPay) {
+        this.cusName = cusName;
+        this.cusId = cusId;
+        this.cusTotalTime = cusTotalTime;
+        this.cusTotalPay = cusTotalPay;
+    }
+
+    public String getCusName() {
+        return cusName;
+    }
+
+    public void setCusName(String cusName) {
+        this.cusName = cusName;
+    }
+
+    public String getCusId() {
+        return cusId;
+    }
+
+    public void setCusId(String cusId) {
+        this.cusId = cusId;
+    }
+
+    public Integer getCusTotalTime() {
+        return cusTotalTime;
+    }
+
+    public void setCusTotalTime(Integer cusTotalTime) {
+        this.cusTotalTime = cusTotalTime;
+    }
+
+    public Integer getCusTotalPay() {
+        return cusTotalPay;
+    }
+
+    public void setCusTotalPay(Integer cusTotalPay) {
+        this.cusTotalPay = cusTotalPay;
+    }
+
+    public Group getGroup() {
+        return group;
+    }
+
+    public void setGroup(Group group) {
+        this.group = group;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) return true;
+        if (o == null || getClass() != o.getClass()) return false;
+        Customer customer = (Customer) o;
+        return Objects.equals(cusId, customer.cusId);
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(cusId);
+    }
+
+    @Override
+    public String toString() {
+        return "Customer{" +
+                "cusName='" + cusName + '\'' +
+                ", cusId='" + cusId + '\'' +
+                ", cusTotalTime=" + cusTotalTime +
+                ", cusTotalPay=" + cusTotalPay +
+                '}';
+    }
+
+    @Override
+    public int compareTo(Customer o) {
+        return this.cusName.compareTo(o.cusName);
+    }
+}
diff --git a/me/smartstore/customer/Customers.java b/me/smartstore/customer/Customers.java
new file mode 100644
index 00000000..ea5e2b26
--- /dev/null
+++ b/me/smartstore/customer/Customers.java
@@ -0,0 +1,51 @@
+package me.smartstore.customer;
+
+import me.smartstore.arrays.DArray;
+import me.smartstore.group.Group;
+import me.smartstore.group.Groups;
+
+public class Customers extends DArray<Customer> {
+
+    private static Customers allCustomers;
+    private final Groups allGroups = Groups.getInstance();
+
+    public static Customers getInstance() {
+        if (allCustomers == null) {
+            allCustomers = new Customers();
+        }
+        return allCustomers;
+    }
+
+    private Customers() {
+    }
+
+    public void refresh(Customer customer) {
+        int time = customer.getCusTotalTime();
+        int pay = customer.getCusTotalPay();
+        for (int i = 0; i < allGroups.size(); i++) {
+            if (time >= allGroups.get(i).getParameter().getMinTime()
+                    && pay >= allGroups.get(i).getParameter().getMinPay()) {
+                customer.setGroup(allGroups.get(i));
+            }
+        }
+    }
+
+    public void refresh(Groups groups) {
+        for (int i = 0; i < allCustomers.size(); i++) {
+            Customer customer = allCustomers.get(i);
+            Group customerGroup = customer.getGroup();
+            if (customerGroup == null) {
+                continue;
+            }
+            for (int j = 0; j < groups.size(); j++) {
+                Group group = groups.get(j);
+                if (customer.getCusTotalTime() >= group.getParameter().getMinTime()
+                        && customer.getCusTotalPay() >= group.getParameter().getMinPay()) {
+                    customer.setGroup(group);
+                    break;
+                }
+            }
+        }
+    }
+}
+
diff --git a/me/smartstore/exception/ElementNotFoundException.java b/me/smartstore/exception/ElementNotFoundException.java
new file mode 100644
index 00000000..ecebe6f1
--- /dev/null
+++ b/me/smartstore/exception/ElementNotFoundException.java
@@ -0,0 +1,12 @@
+package me.smartstore.exception;
+import me.smartstore.util.Message;
+public class ElementNotFoundException extends RuntimeException {
+    public ElementNotFoundException(){
+        super(Message.ERR_MSG_NULL_ARR_ELEMENT);
+    }
+
+    public ElementNotFoundException(String message){
+        super(message);
+    }
+
+}
diff --git a/me/smartstore/exception/EmptyArrayException.java b/me/smartstore/exception/EmptyArrayException.java
new file mode 100644
index 00000000..3f8005bc
--- /dev/null
+++ b/me/smartstore/exception/EmptyArrayException.java
@@ -0,0 +1,12 @@
+package me.smartstore.exception;
+
+import me.smartstore.util.Message;
+
+public class EmptyArrayException extends RuntimeException {
+    public EmptyArrayException(){
+        super(Message.ERR_MSG_INVALID_ARR_EMPTY);
+    }
+    public EmptyArrayException(String message){
+        super(message);
+    }
+}
diff --git a/me/smartstore/exception/InputEmptyException.java b/me/smartstore/exception/InputEmptyException.java
new file mode 100644
index 00000000..93163bc6
--- /dev/null
+++ b/me/smartstore/exception/InputEmptyException.java
@@ -0,0 +1,15 @@
+package me.smartstore.exception;
+
+
+import me.smartstore.util.Message;
+
+public class InputEmptyException extends RuntimeException {
+
+    public InputEmptyException() {
+        super(Message.ERR_MSG_INVALID_INPUT_EMPTY);
+    }
+
+    public InputEmptyException(String message) {
+        super(message);
+    }
+}
diff --git a/me/smartstore/exception/InputEndException.java b/me/smartstore/exception/InputEndException.java
new file mode 100644
index 00000000..f549a39e
--- /dev/null
+++ b/me/smartstore/exception/InputEndException.java
@@ -0,0 +1,14 @@
+package me.smartstore.exception;
+
+
+import me.smartstore.util.Message;
+
+public class InputEndException extends RuntimeException {
+    public InputEndException() {
+        super(Message.ERR_MSG_INPUT_END);
+    }
+
+    public InputEndException(String message) {
+        super(message);
+    }
+}
diff --git a/me/smartstore/exception/InputFormatException.java b/me/smartstore/exception/InputFormatException.java
new file mode 100644
index 00000000..84faad3c
--- /dev/null
+++ b/me/smartstore/exception/InputFormatException.java
@@ -0,0 +1,14 @@
+package me.smartstore.exception;
+
+
+import me.smartstore.util.Message;
+
+public class InputFormatException extends RuntimeException {
+    public InputFormatException() {
+        super(Message.ERR_MSG_INVALID_INPUT_FORMAT);
+    }
+
+    public InputFormatException(String message) {
+        super(message);
+    }
+}
diff --git a/me/smartstore/exception/InputRangeException.java b/me/smartstore/exception/InputRangeException.java
new file mode 100644
index 00000000..fb2c76df
--- /dev/null
+++ b/me/smartstore/exception/InputRangeException.java
@@ -0,0 +1,14 @@
+package me.smartstore.exception;
+
+
+import me.smartstore.util.Message;
+
+public class InputRangeException extends RuntimeException {
+    public InputRangeException() {
+        super(Message.ERR_MSG_INVALID_INPUT_RANGE);
+    }
+
+    public InputRangeException(String message) {
+        super(message);
+    }
+}
diff --git a/me/smartstore/exception/InputTypeException.java b/me/smartstore/exception/InputTypeException.java
new file mode 100644
index 00000000..d321992f
--- /dev/null
+++ b/me/smartstore/exception/InputTypeException.java
@@ -0,0 +1,14 @@
+package me.smartstore.exception;
+
+
+import me.smartstore.util.Message;
+
+public class InputTypeException extends RuntimeException {
+    public InputTypeException() {
+        super(Message.ERR_MSG_INVALID_INPUT_TYPE);
+    }
+
+    public InputTypeException(String message) {
+        super(message);
+    }
+}
diff --git a/me/smartstore/exception/NullArgumentException.java b/me/smartstore/exception/NullArgumentException.java
new file mode 100644
index 00000000..84d72f58
--- /dev/null
+++ b/me/smartstore/exception/NullArgumentException.java
@@ -0,0 +1,13 @@
+package me.smartstore.exception;
+
+import me.smartstore.util.Message;
+
+public class NullArgumentException extends RuntimeException {
+    public NullArgumentException(){
+        super(Message.ERR_MSG_INVALID_INPUT_NULL);
+    }
+
+    public NullArgumentException(String message){
+        super(message);
+    }
+}
diff --git a/me/smartstore/group/Group.java b/me/smartstore/group/Group.java
new file mode 100644
index 00000000..92182c6a
--- /dev/null
+++ b/me/smartstore/group/Group.java
@@ -0,0 +1,53 @@
+package me.smartstore.group;
+
+import java.util.Objects;
+
+public class Group {
+    private Parameter parameter; // 분류기준
+    private GroupType groupType; // 그룹 타입
+
+    public Group(GroupType groupType) {
+    }
+
+    public Group(Parameter parameter, GroupType groupType) {
+        this.parameter = parameter;
+        this.groupType = groupType;
+    }
+
+    public Parameter getParameter() {
+        return parameter;
+    }
+
+    public void setParameter(Parameter parameter) {
+        this.parameter = parameter;
+    }
+
+    public GroupType getGroupType() {
+        return groupType;
+    }
+
+    public void setGroupType(GroupType groupType) {
+        this.groupType = groupType;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) return true;
+        if (o == null || getClass() != o.getClass()) return false;
+        Group group = (Group) o;
+        return Objects.equals(parameter, group.parameter) && groupType == group.groupType;
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(parameter, groupType);
+    }
+
+    @Override
+    public String toString() {
+        return "Group{" +
+                "parameter=" + parameter +
+                ", groupType=" + groupType +
+                '}';
+    }
+}
diff --git a/me/smartstore/group/GroupType.java b/me/smartstore/group/GroupType.java
new file mode 100644
index 00000000..d6ccca37
--- /dev/null
+++ b/me/smartstore/group/GroupType.java
@@ -0,0 +1,22 @@
+package me.smartstore.group;
+
+public enum GroupType {
+    NONE("해당없음"), GENERAL("일반고객"), VIP("우수고객"), VVIP("최우수고객"),
+    N("해당없음"), G("일반고객"), V("우수고객"), VV("최우수고객");
+
+
+    String groupType = "";
+
+
+    GroupType(String groupType) {
+        this.groupType = groupType;
+    }
+
+    public GroupType replaceFullName() {
+        if (this == N) return NONE;
+        else if (this == G) return GENERAL;
+        else if (this == V) return VIP;
+        else if (this == VV) return VVIP;
+        return this;
+    }
+}
diff --git a/me/smartstore/group/Groups.java b/me/smartstore/group/Groups.java
new file mode 100644
index 00000000..e926efd9
--- /dev/null
+++ b/me/smartstore/group/Groups.java
@@ -0,0 +1,27 @@
+package me.smartstore.group;
+
+
+import me.smartstore.arrays.DArray;
+
+public class Groups extends DArray<Group> {
+    // singleton
+    private static Groups allGroups;
+
+    public static Groups getInstance() {
+        if (allGroups == null) {
+            allGroups = new Groups();
+        }
+        return allGroups;
+    }
+
+    private Groups() {}
+
+    public Group find(GroupType groupType) {
+        for (int i = 0; i < allGroups.size(); i++) {
+            if (allGroups.get(i).getGroupType() == groupType) {
+                return allGroups.get(i);
+            }
+        }
+        return  null;
+    }
+}
diff --git a/me/smartstore/group/Parameter.java b/me/smartstore/group/Parameter.java
new file mode 100644
index 00000000..9b711f41
--- /dev/null
+++ b/me/smartstore/group/Parameter.java
@@ -0,0 +1,54 @@
+package me.smartstore.group;
+
+import java.util.Objects;
+
+public class Parameter {
+    private Integer minTime;
+    private Integer minPay;
+
+
+    public Parameter() {
+    }
+
+    public Parameter(Integer minTime, Integer minPay) {
+        this.minTime = minTime;
+        this.minPay = minPay;
+    }
+
+    public Integer getMinTime() {
+        return minTime;
+    }
+
+    public void setMinTime(Integer minTime) {
+        this.minTime = minTime;
+    }
+
+    public Integer getMinPay() {
+        return minPay;
+    }
+
+    public void setMinPay(Integer minPay) {
+        this.minPay = minPay;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) return true;
+        if (o == null || getClass() != o.getClass()) return false;
+        Parameter parameter = (Parameter) o;
+        return Objects.equals(minTime, parameter.minTime) && Objects.equals(minPay, parameter.minPay);
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(minTime, minPay);
+    }
+
+    @Override
+    public String toString() {
+        return "Parameter{" +
+                "minTime=" + minTime +
+                ", minPay=" + minPay +
+                '}';
+    }
+}
diff --git a/me/smartstore/menu/CustomerMenu.java b/me/smartstore/menu/CustomerMenu.java
new file mode 100644
index 00000000..093e6599
--- /dev/null
+++ b/me/smartstore/menu/CustomerMenu.java
@@ -0,0 +1,180 @@
+package me.smartstore.menu;
+
+import me.smartstore.customer.Customer;
+import me.smartstore.customer.Customers;
+import me.smartstore.exception.EmptyArrayException;
+import me.smartstore.exception.InputEndException;
+import me.smartstore.exception.InputRangeException;
+import me.smartstore.group.Groups;
+import me.smartstore.util.Message;
+
+
+public class CustomerMenu implements Menu {
+    private final Groups allGroups = Groups.getInstance();
+    private final Customers allCustomers = Customers.getInstance();
+    // singleton
+    private static CustomerMenu customerMenu;
+
+    public static CustomerMenu getInstance() {
+        if (customerMenu == null) {
+            customerMenu = new CustomerMenu();
+        }
+        return customerMenu;
+    }
+
+    private CustomerMenu() {
+    }
+
+    @Override
+    public void manage() {
+        while (true) { // 서브 메뉴 페이지를 유지하기 위한 while
+            int choice = chooseMenu(new String[]{
+                    "Add Customer",
+                    "View Customer",
+                    "Update Customer",
+                    "Delete Customer",
+                    "Back"});
+
+            if (choice == 1) addCustomer();
+            else if (choice == 2) {
+                viewCustomer();
+            } else if (choice == 3) {
+                updateCustomer();
+            } else if (choice == 4) {
+                deleteCustomer();
+            } else break;
+        }
+    }
+
+    public void addCustomer() {
+
+        System.out.println("Enter customer name: ");
+        String name = nextLine();
+        System.out.println("Enter customer ID: ");
+        String id = nextLine();
+        for (int i = 0; i < allCustomers.size(); i++) {
+            if (allCustomers.get(i).getCusId().equals(id)) {
+                System.out.println("ID already exists");
+                return;
+            }
+        }
+        System.out.println("Enter total time");
+        int time;
+        while (true) {
+            try {
+                time = Integer.parseInt(nextLine());
+                if (time < 0) throw new InputRangeException();
+                break;
+            } catch (NumberFormatException e) {
+                System.out.println(Message.ERR_MSG_INVALID_INPUT_FORMAT);
+            } catch (InputRangeException e) {
+                System.out.println(Message.ERR_MSG_INVALID_INPUT_RANGE);
+            }
+        }
+
+        System.out.println("Enter total pay");
+        int pay;
+        while (true) {
+            try {
+                pay = Integer.parseInt(nextLine());
+                if (pay < 0) throw new InputRangeException();
+                break;
+            } catch (NumberFormatException e) {
+                System.out.println(Message.ERR_MSG_INVALID_INPUT_FORMAT);
+            } catch (InputRangeException e) {
+                System.out.println(Message.ERR_MSG_INVALID_INPUT_RANGE);
+            }
+        }
+
+        Customer customer = new Customer(name, id, time, pay);
+        allCustomers.add(customer);
+        allCustomers.refresh(customer);
+        System.out.println("** Add SUCCESS **" + customer);
+
+    }
+
+    public void viewCustomer() {
+        try {
+            for (int i = 0; i < allCustomers.size(); i++) {
+                System.out.println(allCustomers.get(i).toString());
+            }
+        } catch (EmptyArrayException e) {
+            System.out.println(Message.ERR_MSG_NULL_ARR_ELEMENT);
+        }
+    }
+
+    public void updateCustomer() {
+        Customer customer = null;
+
+        System.out.println("Enter customer ID: ");
+        String id = scanner.nextLine();
+
+        for (int i = 0; i < allCustomers.size(); i++) {
+            if (id != null && allCustomers.get(i).getCusId().equals(id)) {
+                customer = allCustomers.get(i);
+                System.out.println(customer.toString());
+                break;
+            }
+        }
+        if (customer == null) {
+            System.out.println("customer ID does not exist");
+            return;
+        }
+
+        System.out.println("***** Choose Update *****");
+        while (true) {
+            try {
+                int choice = chooseMenu(new String[]{
+                        "Customer Name",
+                        "Customer Total Time",
+                        "Customer Total Pay",
+                        "Back"});
+
+                if (choice == 1) {
+                    System.out.println("Update customer Name : ");
+                    String setName = scanner.nextLine();
+                    customer.setCusName(setName);
+                } else if (choice == 2) {
+                    System.out.println("Update customer Total time : ");
+                    int setTime = Integer.parseInt(scanner.nextLine());
+                    customer.setCusTotalTime(setTime);
+                } else if (choice == 3) {
+                    System.out.println("Update customer Total Pay : ");
+                    int setPay = Integer.parseInt(scanner.nextLine());
+                    customer.setCusTotalPay(setPay);
+                } else break;
+                System.out.println(customer);
+            } catch (InputEndException e) {
+                System.out.println(Message.ERR_MSG_INPUT_END);
+            }
+            allCustomers.refresh(allGroups);
+        }
+    }
+
+
+    public void deleteCustomer() {
+
+        System.out.println("Enter customer ID : ");
+        String id = scanner.nextLine();
+        int index = -1;
+        try {
+            for (int i = 0; i < allCustomers.size(); i++) {
+                if (id != null && allCustomers.get(i).getCusId().equals(id)) {
+                    index = i;
+                    break;
+                }
+            }
+        } catch (EmptyArrayException e) {
+            System.out.println(Message.ERR_MSG_INVALID_ARR_EMPTY);
+        }
+
+        if (index == -1) {
+            System.out.println("customer ID does not exist");
+        }
+        try {
+            System.out.println("**Delete Success**" + allCustomers.pop(index));
+        } catch (IndexOutOfBoundsException e) {
+            System.out.println(Message.ERR_MSG_INVALID_ARR_INDEX);
+        }
+    }
+}
diff --git a/me/smartstore/menu/GroupMenu.java b/me/smartstore/menu/GroupMenu.java
new file mode 100644
index 00000000..6736e7ec
--- /dev/null
+++ b/me/smartstore/menu/GroupMenu.java
@@ -0,0 +1,169 @@
+package me.smartstore.menu;
+
+
+import me.smartstore.customer.Customers;
+import me.smartstore.exception.EmptyArrayException;
+import me.smartstore.exception.InputEndException;
+import me.smartstore.exception.InputRangeException;
+import me.smartstore.group.Group;
+import me.smartstore.group.GroupType;
+import me.smartstore.group.Groups;
+import me.smartstore.group.Parameter;
+import me.smartstore.util.Message;
+
+public class GroupMenu implements Menu {
+    private final Groups allGroups = Groups.getInstance();
+    private final Customers allCustomers = Customers.getInstance();
+    // singleton
+    private static GroupMenu groupMenu;
+
+    public static GroupMenu getInstance() {
+        if (groupMenu == null) {
+            groupMenu = new GroupMenu();
+        }
+        return groupMenu;
+    }
+
+    private GroupMenu() {
+    }
+
+    @Override
+    public void manage() {
+        while (true) {
+            int choice = chooseMenu(new String[]{
+                    "Set Parameter",
+                    "View Parameter",
+                    "Update Parameter",
+                    "Back"});
+
+            if (choice == 1) setParameter();
+            else if (choice == 2) {
+                viewParameter();
+            } else if (choice == 3) {
+                updateParameter();
+            } else break;
+        }
+    }
+
+    public GroupType chooseGroup() {
+        while (true) {
+            try {
+                System.out.print("Which group (GENERAL (G), VIP (V), VVIP (VV))? ");
+                String choice = nextLine(Message.END_MSG);
+
+                GroupType groupType = GroupType.valueOf(choice).replaceFullName();
+                return groupType;
+            } catch (InputEndException e) {
+                System.out.println(Message.ERR_MSG_INPUT_END);
+                return null;
+            } catch (IllegalArgumentException e) {
+                System.out.println(Message.ERR_MSG_INVALID_INPUT_RANGE);
+            }
+        }
+    }
+
+
+    public void setParameter() {
+        while (true) {
+            GroupType groupType = chooseGroup();
+            if (groupType == null) {
+                break;
+            }
+            Group group = allGroups.find(groupType);
+            if (group != null && group.getParameter() != null) {
+                System.out.println("\n" + group.getGroupType() + " group already exists.");
+                System.out.println("\n" + group);
+            } else {
+                Parameter parameter = new Parameter();
+                System.out.println("Enter min time");
+                int time;
+                while (true) {
+                    try {
+                        time = Integer.parseInt(nextLine());
+                        if (time < 0) throw new InputRangeException();
+                        break;
+                    } catch (NumberFormatException e) {
+                        System.out.println(Message.ERR_MSG_INVALID_INPUT_FORMAT);
+                    } catch (InputRangeException e) {
+                        System.out.println(Message.ERR_MSG_INVALID_INPUT_RANGE);
+                    }
+                }
+                parameter.setMinTime(time);
+
+                System.out.println("Enter min pay");
+                int pay;
+                while (true) {
+                    try {
+                        pay = Integer.parseInt(nextLine());
+                        if (pay < 0) throw new InputRangeException();
+                        break;
+                    } catch (NumberFormatException e) {
+                        System.out.println(Message.ERR_MSG_INVALID_INPUT_FORMAT);
+                    } catch (InputRangeException e) {
+                        System.out.println(Message.ERR_MSG_INVALID_INPUT_RANGE);
+                    }
+                }
+                parameter.setMinPay(pay);
+
+                group.setParameter(parameter);
+                allCustomers.refresh(allGroups);
+            }
+        }
+    }
+
+    public void viewParameter() {
+        while (true) {
+            GroupType groupType = chooseGroup();
+            if (groupType == null) {
+                break;
+            }
+            try {
+                Group group = allGroups.find(groupType);
+                System.out.println(groupType);
+                System.out.println(group.getParameter());
+            } catch (EmptyArrayException e) {
+                System.out.println(Message.ERR_MSG_INVALID_ARR_EMPTY);
+            }
+        }
+    }
+
+    public void updateParameter() {
+        while (true) {
+            GroupType groupType = chooseGroup();
+            if (groupType == null) {
+                break;
+            }
+
+            Group group = allGroups.find(groupType);
+            if (group == null || group.getParameter() == null) {
+                System.out.println("\n" + groupType + " group does not exist or parameter is not set.");
+            } else {
+                System.out.println("\nCurrent parameter: " + group.getParameter());
+
+                while (true) {
+                    try {
+                        System.out.print("Enter minimum time \n");
+                        int minTime = Integer.parseInt(nextLine(Message.END_MSG));
+
+                        System.out.print("Enter minimum pay \n");
+                        int minPay = Integer.parseInt(nextLine(Message.END_MSG));
+
+                        group.getParameter().setMinTime(minTime);
+                        group.getParameter().setMinPay(minPay);
+
+                        allCustomers.refresh(allGroups);
+
+                        System.out.println("\nUpdated parameter: " + group.getParameter());
+                        break;
+                    } catch (NumberFormatException e) {
+                        System.out.println(Message.ERR_MSG_INVALID_INPUT_TYPE);
+                    } catch (InputEndException e) {
+                        System.out.println(Message.ERR_MSG_INPUT_END);
+                        break;
+                    }
+                }
+            }
+            allCustomers.refresh(allGroups);
+        }
+    }
+}
\ No newline at end of file
diff --git a/me/smartstore/menu/MainMenu.java b/me/smartstore/menu/MainMenu.java
new file mode 100644
index 00000000..a7768657
--- /dev/null
+++ b/me/smartstore/menu/MainMenu.java
@@ -0,0 +1,39 @@
+package me.smartstore.menu;
+
+public class MainMenu implements Menu {
+
+    private final CustomerMenu customerMenu = CustomerMenu.getInstance();
+    private final GroupMenu groupMenu = GroupMenu.getInstance();
+    private final SummaryMenu summaryMenu = SummaryMenu.getInstance();
+
+    // singleton
+    private static MainMenu mainMenu;
+
+    public static MainMenu getInstance() {
+        if (mainMenu == null) {
+            mainMenu = new MainMenu();
+        }
+        return mainMenu;
+    }
+
+    private MainMenu() {}
+
+    @Override
+    public void manage() {
+        while ( true ) { // 프로그램 실행 while
+            int choice = mainMenu.chooseMenu(new String[] {
+                    "Parameter",
+                    "Customer",
+                    "Classification Summary",
+                    "Quit"});
+
+            if (choice == 1) groupMenu.manage();
+            else if (choice == 2) customerMenu.manage();
+            else if (choice == 3) summaryMenu.manage();
+            else { // choice == 4
+                System.out.println("Program Finished");
+                break;
+            }
+        }
+    }
+}
diff --git a/me/smartstore/menu/Menu.java b/me/smartstore/menu/Menu.java
new file mode 100644
index 00000000..5dc42701
--- /dev/null
+++ b/me/smartstore/menu/Menu.java
@@ -0,0 +1,49 @@
+package me.smartstore.menu;
+
+
+import me.smartstore.exception.InputEndException;
+import me.smartstore.exception.InputRangeException;
+import me.smartstore.util.Message;
+
+import java.util.InputMismatchException;
+import java.util.Scanner;
+
+public interface Menu {
+    Scanner scanner = new Scanner(System.in);
+
+    default String nextLine() { // 하나의 프로그램 상에서 nextLine() 함수를 통해서 사용자 입력을 받음
+        return scanner.nextLine().toUpperCase();
+    }
+
+    default String nextLine(String end) {
+        System.out.println("** Press 'end', if you want to exit! **");
+        String str = scanner.nextLine().toUpperCase();
+        if (str.equals(end)) throw new InputEndException();
+        return str;
+    }
+
+    default int chooseMenu(String[] menus) {
+        while ( true ) { // 예외 복구 while
+            try {
+                System.out.println("===============================");
+                for (int i = 0; i < menus.length; i++) {
+                    System.out.printf(" %d. %s\n", i + 1, menus[i]);
+                }
+                System.out.println("===============================");
+                System.out.print("Choose One: ");
+                int choice = Integer.parseInt(nextLine());
+                if (choice >= 1 && choice <= menus.length) return choice;
+                throw new InputRangeException(); // choice 가 범위에 벗어남
+
+            } catch (InputMismatchException e) {
+                System.out.println(Message.ERR_MSG_INVALID_INPUT_FORMAT);
+
+            } catch (InputRangeException e) {
+                System.out.println(Message.ERR_MSG_INVALID_INPUT_RANGE);
+
+            }
+        }
+    }
+
+    void manage(); // 각 서브메뉴들을 관리하는 함수 (각 서브메뉴의 최상위 메뉴)
+}
diff --git a/me/smartstore/menu/SummaryMenu.java b/me/smartstore/menu/SummaryMenu.java
new file mode 100644
index 00000000..dc2802c8
--- /dev/null
+++ b/me/smartstore/menu/SummaryMenu.java
@@ -0,0 +1,104 @@
+package me.smartstore.menu;
+
+import me.smartstore.customer.Customer;
+import me.smartstore.customer.Customers;
+import me.smartstore.exception.EmptyArrayException;
+import me.smartstore.group.Groups;
+import me.smartstore.util.Message;
+
+import java.util.Arrays;
+import java.util.Comparator;
+
+
+public class SummaryMenu implements Menu {
+    private static SummaryMenu summaryMenu;
+    private final Groups allGroups = Groups.getInstance();
+    private final Customers allCustomers = Customers.getInstance();
+
+    public static SummaryMenu getInstance() {
+        if (summaryMenu == null) {
+            summaryMenu = new SummaryMenu();
+        }
+        return summaryMenu;
+    }
+
+    private SummaryMenu() {
+    }
+
+    @Override
+    public void manage() {
+        while (true) {
+            int choice = chooseMenu(new String[]{
+                    "Summary",
+                    "Summary (Sorted By Name)",
+                    "Summary (Sorted By Time)",
+                    "Summary (Sorted By Pay)",
+                    "Back"});
+            if (choice == 1) summary();
+            else if (choice == 2) sortedByName();
+            else if (choice == 3) sortedByTime();
+            else if (choice == 4) sortedByPay();
+            else break;
+        }
+    }
+
+    private void summary() {
+        try {
+            for (int i = 0; i < allCustomers.size(); i++) {
+                System.out.println(allCustomers.get(i).toString());
+            }
+        } catch (EmptyArrayException e) {
+            System.out.println(Message.ERR_MSG_NULL_ARR_ELEMENT);
+        }
+    }
+
+    public void sortedByName() {
+        try {
+            Customer[] customers = new Customer[allCustomers.size()];
+            for (int i = 0; i < customers.length; i++) {
+                customers[i] = allCustomers.get(i);
+            }
+            Arrays.sort(customers);
+
+            for (Customer customer : customers) {
+                System.out.println(customer.toString());
+            }
+        } catch (EmptyArrayException e) {
+            System.out.println(Message.ERR_MSG_INVALID_ARR_EMPTY);
+        }
+    }
+
+    public void sortedByTime() {
+        try {
+            Customer[] customers = new Customer[allCustomers.size()];
+            for (int i = 0; i < customers.length; i++) {
+                customers[i] = allCustomers.get(i);
+            }
+            Arrays.sort(customers, Comparator.comparing(Customer::getCusTotalTime));
+
+            for (Customer customer : customers) {
+                System.out.println(customer.toString());
+            }
+        } catch (EmptyArrayException e) {
+            System.out.println(Message.ERR_MSG_NULL_ARR_ELEMENT);
+        }
+    }
+
+    public void sortedByPay() {
+        try {
+            Customer[] customers = new Customer[allCustomers.size()];
+            for (int i = 0; i < customers.length; i++) {
+                customers[i] = allCustomers.get(i);
+            }
+            Arrays.sort(customers, Comparator.comparing(Customer::getCusTotalPay));
+
+            for (Customer customer : customers) {
+                System.out.println(customer.toString());
+            }
+        } catch (EmptyArrayException e) {
+            System.out.println(Message.ERR_MSG_NULL_ARR_ELEMENT);
+        }
+    }
+}
+
+
diff --git a/me/smartstore/util/Message.java b/me/smartstore/util/Message.java
new file mode 100644
index 00000000..e3c04642
--- /dev/null
+++ b/me/smartstore/util/Message.java
@@ -0,0 +1,14 @@
+package me.smartstore.util;
+
+public interface Message {
+    String ERR_MSG_INVALID_ARR_EMPTY = "No Customers. Please input one first.";
+    String ERR_MSG_NULL_ARR_ELEMENT = "Elements in Array has null. Array can't be sorted.";
+    String ERR_MSG_INVALID_INPUT_NULL = "Null Input. Please input something.";
+    String ERR_MSG_INVALID_INPUT_EMPTY = "Empty Input. Please input something.";
+    String ERR_MSG_INVALID_INPUT_RANGE = "Invalid Input. Please try again.";
+    String ERR_MSG_INVALID_INPUT_TYPE = "Invalid Type for Input. Please try again.";
+    String ERR_MSG_INVALID_INPUT_FORMAT = "Invalid Format for Input. Please try again.";
+    String ERR_MSG_INPUT_END = "END is pressed. Exit this menu.";
+    String END_MSG = "END";
+    String ERR_MSG_INVALID_ARR_INDEX = "Invaild Input. Index out of Bounds.";
+}