diff --git a/src/me/day05/practice/Practice01/AuthMethod.java b/src/me/day05/practice/Practice01/AuthMethod.java
new file mode 100644
index 0000000..d03c0ee
--- /dev/null
+++ b/src/me/day05/practice/Practice01/AuthMethod.java
@@ -0,0 +1,8 @@
+package me.day05.practice.Practice01;
+
+public enum AuthMethod {
+    FINGERPRINT, PATTERN, PIN, FACE
+
+}
+
+
diff --git a/src/me/day05/practice/Practice01/CompanyName.java b/src/me/day05/practice/Practice01/CompanyName.java
new file mode 100644
index 0000000..70e7fa7
--- /dev/null
+++ b/src/me/day05/practice/Practice01/CompanyName.java
@@ -0,0 +1,5 @@
+package me.day05.practice.Practice01;
+
+public enum CompanyName {
+     SAMSUNG, LG, APPLE
+}
diff --git a/src/me/day05/practice/Practice01/Electronic.java b/src/me/day05/practice/Practice01/Electronic.java
new file mode 100644
index 0000000..3cd581e
--- /dev/null
+++ b/src/me/day05/practice/Practice01/Electronic.java
@@ -0,0 +1,123 @@
+package me.day05.practice.Practice01;
+
+import java.time.LocalDate;
+import java.time.ZoneId;
+import java.time.format.DateTimeFormatter;
+import java.util.Arrays;
+import java.util.Objects;
+
+public class Electronic {
+    private static int serialNum = 0;
+    private String productNo;
+    private String modelName;
+    private CompanyName companyName;
+    private LocalDate dateOfMade;
+    private AuthMethod[] authMethod;
+
+    private Electronic() {
+        serialNum++;
+        setProductNo();
+    }
+
+    public Electronic(String productNo) {
+        this.productNo = productNo;
+    }
+
+    public Electronic(String modelName, CompanyName companyName, LocalDate dateOfMade, AuthMethod[] authMethod) {
+        this();
+        this.modelName = modelName;
+        this.companyName = companyName;
+        this.dateOfMade = dateOfMade;
+        this.authMethod = authMethod;
+    }
+
+    public String getProductNo() {
+        return productNo;
+    }
+
+    private String setProductNo() {
+
+        StringBuilder sb = new StringBuilder(10);
+        sb.append(LocalDate.now().format(DateTimeFormatter.ofPattern("yyMMdd")));
+
+        if ( (int)Math.log10(serialNum)+1 == 1){
+            sb.append("000");
+            sb.append(serialNum);
+        } else if  ( (int)Math.log10(serialNum)+1 == 2) {
+            sb.append("00");
+            sb.append(serialNum);
+        } else if  ( (int)Math.log10(serialNum)+1 == 3) {
+            sb.append("0");
+            sb.append(serialNum);
+        } else {
+            sb.append(serialNum);
+        }
+        String order = String.format("%04d", serialNum);
+        String date = LocalDate.now(ZoneId.systemDefault()).toString().replace("-", "").substring(2);
+
+        productNo = String.valueOf(sb);
+        return productNo;
+    }
+
+    public String getModelName() {
+        return modelName;
+    }
+
+    public void setModelName(String modelName) {
+        this.modelName = modelName;
+    }
+
+    public CompanyName getCompanyName() {
+        return companyName;
+    }
+
+    public void setCompanyName(CompanyName companyName) {
+        this.companyName = companyName;
+    }
+
+    public LocalDate getDateOfMade() {
+        return dateOfMade;
+    }
+
+    public void setDateOfMade(LocalDate dateOfMade) {
+        this.dateOfMade = dateOfMade;
+    }
+
+    public AuthMethod[] getAuthMethod() {
+        return authMethod;
+    }
+
+    public void setAuthMethod(AuthMethod[] authMethod) {
+        this.authMethod = authMethod;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) return true;
+        if (o == null || getClass() != o.getClass()) return false;
+        Electronic that = (Electronic) o;
+        return Objects.equals(productNo, that.productNo) && Objects.equals(modelName, that.modelName) && companyName == that.companyName && Objects.equals(dateOfMade, that.dateOfMade) && Objects.equals(authMethod, that.authMethod);
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(productNo, modelName, companyName, dateOfMade, authMethod);
+    }
+
+    @Override
+    public String toString() {
+        return "Electronic{" +
+                "productNo='" + productNo + '\'' +
+                ", modelName='" + modelName + '\'' +
+                ", companyName=" + companyName +
+                ", dateOfMade=" + dateOfMade +
+                ", authMethod=" + Arrays.toString(authMethod) +
+                '}';
+    }
+
+    public int authMethodSize(){
+        AuthMethod[] values = AuthMethod.values();
+
+        return values.length;
+    }
+}
diff --git a/src/me/day05/practice/Practice01/User.java b/src/me/day05/practice/Practice01/User.java
new file mode 100644
index 0000000..ffa87f2
--- /dev/null
+++ b/src/me/day05/practice/Practice01/User.java
@@ -0,0 +1,124 @@
+package me.day05.practice.Practice01;
+
+import java.time.LocalDate;
+import java.time.LocalDateTime;
+import java.util.Arrays;
+import java.util.Objects;
+
+public class User {
+    private String userId;
+    private String userPassword;
+    private String userPhoneNumber;
+    private String userEmail;
+    private LocalDate userBirthDate;
+    private String[] electronicDevices;
+    private LocalDateTime registerTime;
+
+    public User() {
+        registerTime = LocalDateTime.now();
+    }
+
+    public User(String userId) {
+        this.userId = userId;
+    }
+
+    public User(String userId, String userPassword) {
+        this();
+        this.userId = userId;
+        this.userPassword = userPassword;
+    }
+
+    public User(String userId, String userPassword, String userPhoneNumber, String userEmail, LocalDate userBirthDate, String[] electronicDevices) {
+        this();
+        this.userId = userId;
+        this.userPassword = userPassword;
+        this.userPhoneNumber = userPhoneNumber;
+        this.userEmail = userEmail;
+        this.userBirthDate = userBirthDate;
+        this.electronicDevices = electronicDevices;
+    }
+
+    public String getUserId() {
+        return userId;
+    }
+
+    public void setUserId(String userId) {
+        this.userId = userId;
+    }
+
+    public String getUserPassword() {
+        return userPassword;
+    }
+
+    public void setUserPassword(String userPassword) {
+        this.userPassword = userPassword;
+    }
+
+    public String getUserPhoneNumber() {
+        return userPhoneNumber;
+    }
+
+    public void setUserPhoneNumber(String userPhoneNumber) {
+        this.userPhoneNumber = userPhoneNumber;
+    }
+
+    public String getUserEmail() {
+        return userEmail;
+    }
+
+    public void setUserEmail(String userEmail) {
+        this.userEmail = userEmail;
+    }
+
+    public LocalDate getUserBirthDate() {
+        return userBirthDate;
+    }
+
+    public void setUserBirthDate(LocalDate userBirthDate) {
+        this.userBirthDate = userBirthDate;
+    }
+
+    public String[] getElectronicDevices() {
+        return electronicDevices;
+    }
+
+    public void setElectronicDevices(String[] electronicDevices) {
+        this.electronicDevices = electronicDevices;
+    }
+
+    public LocalDateTime getRegisterTime() {
+        return registerTime;
+    }
+
+    public void setRegisterTime(LocalDateTime registerTime) {
+        this.registerTime = registerTime;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) return true;
+        if (o == null || getClass() != o.getClass()) return false;
+        User user = (User) o;
+        return Objects.equals(userId, user.userId) && Objects.equals(userPassword, user.userPassword) && Objects.equals(userPhoneNumber, user.userPhoneNumber) && Objects.equals(userEmail, user.userEmail) && Objects.equals(userBirthDate, user.userBirthDate) && Arrays.equals(electronicDevices, user.electronicDevices) && Objects.equals(registerTime, user.registerTime);
+    }
+
+    @Override
+    public int hashCode() {
+        int result = Objects.hash(userId, userPassword, userPhoneNumber, userEmail, userBirthDate, registerTime);
+        result = 31 * result + Arrays.hashCode(electronicDevices);
+        return result;
+    }
+
+    @Override
+    public String toString() {
+        return "User{" +
+                "userId='" + userId + '\'' +
+                ", userPassword='" + userPassword + '\'' +
+                ", userPhoneNumber='" + userPhoneNumber + '\'' +
+                ", userEmail='" + userEmail + '\'' +
+                ", userBirthDate=" + userBirthDate +
+                ", electronicDevices=" + Arrays.toString(electronicDevices) +
+                ", registerTime=" + registerTime +
+                '}';
+    }
+}
diff --git a/src/me/day05/practice/Practice01/userTest.java b/src/me/day05/practice/Practice01/userTest.java
new file mode 100644
index 0000000..a29f468
--- /dev/null
+++ b/src/me/day05/practice/Practice01/userTest.java
@@ -0,0 +1,64 @@
+package me.day05.practice.Practice01;
+
+import me.day05.practice.Practice02.Users;
+import me.day05.practice.Practice03.Electronics;
+
+import java.time.LocalDate;
+import java.util.Arrays;
+
+import static me.day05.practice.Practice01.AuthMethod.*;
+
+
+public class userTest {
+    public static void main(String[] args) {
+        User userSong = new User("Song", "a1234");
+
+        System.out.println(userSong);
+
+        String[] electronicDevices = {"GalaxyS", "GalaxyTablet"};
+
+        User userTae = new User("Tae","b5678",
+                "010-8885-9677","ussu1112@naver.com", LocalDate.of(1995,8,29), electronicDevices);
+
+        System.out.println(userTae);
+
+
+        //Users user = new Users(); - 싱글톤 패턴이기 때문에 불가능
+        Users user = Users.getInstance();
+        User userHyoung = user.createUser("Hyoung", "c8901");
+        User userTaeHyoung = user.createUser("TaeHyoung", "d9021");
+        User userSonng = user.createUser("Tae","b5678",
+                "010-8885-9677","ussu1112@naver.com", LocalDate.of(1995,8,29), electronicDevices);
+
+        System.out.println(userHyoung);
+        System.out.println(userTaeHyoung);
+        System.out.println(userSonng);
+        System.out.println(Arrays.toString(user.getUserList()));
+        System.out.println(user.findByUserId("Hyoung"));
+        System.out.println(Users.copy(userHyoung));
+
+        System.out.println("===========================");
+
+        Electronics electronics = Electronics.getInstance();
+
+        AuthMethod[] authArray = {FINGERPRINT, PIN};
+        AuthMethod[] authArray2 = {PATTERN, FACE};
+
+        Electronic electronic = electronics.createElectronic("Galaxy", CompanyName.SAMSUNG, LocalDate.now(), authArray);
+        Electronic electronic2 = electronics.createElectronic("IPhone", CompanyName.APPLE, LocalDate.now(), authArray2);
+
+        System.out.println(electronic);
+        System.out.println(electronic2);
+
+        System.out.println("===========================");
+
+        Electronic electronicsA = electronics.createElectronic("Galaxy", CompanyName.SAMSUNG, LocalDate.now(), authArray);
+        Electronic electronicsB = electronics.createElectronic("IPhone", CompanyName.APPLE, LocalDate.now(), authArray2);
+
+        System.out.println(electronicsA);
+        System.out.println(electronics.findByProductNo("2304250003"));
+        System.out.println(Arrays.toString(electronics.groupByCompanyName(CompanyName.SAMSUNG)));
+        System.out.println(Arrays.toString(electronicsB.getAuthMethod()));
+        System.out.println(Arrays.toString(electronics.groupByAuthMethod(FINGERPRINT)));
+    }
+}
diff --git a/src/me/day05/practice/Practice02/Users.java b/src/me/day05/practice/Practice02/Users.java
new file mode 100644
index 0000000..2aee79b
--- /dev/null
+++ b/src/me/day05/practice/Practice02/Users.java
@@ -0,0 +1,114 @@
+package me.day05.practice.Practice02;
+
+import me.day05.practice.Practice01.User;
+
+import java.time.LocalDate;
+import java.util.Arrays;
+import java.util.Objects;
+
+public class Users{
+
+    /*
+     * Q. Users 클래스의 객체를 싱글톤으로 생성하는 함수를 작성하시오.
+     * */
+    private final int arrSize = 10;
+    private User[] userList = new User[arrSize];
+    private static Users instance; // 정적 참조 변수
+
+    private Users() {
+        // private 생성자
+    }
+
+    // 객체 변환 정적 메서드
+    public static Users getInstance() {
+        if(instance == null){
+            instance = new Users();
+        }
+
+        return instance;
+    }
+
+    public User createUser(String userId, String userPassword){
+        User user = new User(userId, userPassword);
+        for (int i = 0; i < userList.length; i++){
+            if (userList[i] == null){
+                userList[i] = user;
+                break;
+            }
+        }
+        return user;
+    }
+
+    public User createUser(String userId, String userPassword, String userPhoneNumber, String userEmail, LocalDate userBirthDate, String[] electronicDevices){
+        User user = new User(userId, userPassword, userPhoneNumber, userEmail, userBirthDate, electronicDevices);
+        for (int i = 0; i < userList.length; i++){
+            if (userList[i] == null){
+                userList[i] = user;
+                break;
+            }
+        }
+        return user;
+    }
+
+    /*
+    * Q. 회원 아이디 userId를 통해 인자로 주어진 회원번호에 해당하는 회원을 반환하는 함수를 작성하시오.
+    * */
+    public User findByUserId(String userId){
+        User newUser = new User(userId);
+        for (User user : userList) {
+            if (user.getUserId().equals(userId)) {
+                newUser = user;
+                System.out.println(user);
+                break;
+            }
+        }
+        return newUser;
+    }
+
+    /*
+    * Q. 인자로 주어진 회원 정보를 깊은 복사 (deepCopy) 하는 함수를 작성하시오.*/
+
+    public static User copy(User user) {
+        User copiedUser = new User();
+
+        copiedUser.setUserId(user.getUserId());
+        copiedUser.setUserPassword(user.getUserPassword());
+        copiedUser.setUserPhoneNumber(user.getUserPhoneNumber());
+        copiedUser.setUserEmail(user.getUserEmail());
+        copiedUser.setUserBirthDate(user.getUserBirthDate());
+        copiedUser.setElectronicDevices(user.getElectronicDevices());
+
+        return copiedUser;
+    }
+
+    public User[] getUserList() {
+        return userList;
+    }
+
+    public void setUserList(User[] userList) {
+        this.userList = userList;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) return true;
+        if (o == null || getClass() != o.getClass()) return false;
+        Users users = (Users) o;
+        return Arrays.equals(userList, users.userList);
+    }
+
+    @Override
+    public int hashCode() {
+        int result = Objects.hash(arrSize);
+        result = 31 * result + Arrays.hashCode(userList);
+        return result;
+    }
+
+    @Override
+    public String toString() {
+        return "Users{" +
+                "arrSize=" + arrSize +
+                ", userList=" + Arrays.toString(userList) +
+                '}';
+    }
+}
diff --git a/src/me/day05/practice/Practice03/Electronics.java b/src/me/day05/practice/Practice03/Electronics.java
new file mode 100644
index 0000000..5c6c193
--- /dev/null
+++ b/src/me/day05/practice/Practice03/Electronics.java
@@ -0,0 +1,135 @@
+package me.day05.practice.Practice03;
+
+import me.day05.practice.Practice01.AuthMethod;
+import me.day05.practice.Practice01.CompanyName;
+import me.day05.practice.Practice01.Electronic;
+
+import java.time.LocalDate;
+import java.util.Arrays;
+import java.util.Objects;
+
+public class Electronics {
+
+    /*
+    * Q. Electronics 클래스의 객체를 싱글톤으로 생성하는 함수를 작성하시오.
+    * */
+    final int arrSize = 10;
+    private static Electronics electronics;
+    private Electronic[] electronicList = new Electronic[arrSize];
+
+    private Electronics() {
+    }
+
+    public static Electronics getInstance() {
+        if (electronics == null){
+            electronics = new Electronics();
+        }
+        return electronics;
+    }
+
+    public Electronic createElectronic(String modelName, CompanyName companyName, LocalDate dateOfMade, AuthMethod[] authMethod){
+        Electronic electronic = new Electronic(modelName, companyName, dateOfMade, authMethod);
+
+        for (int i = 0; i < electronicList.length; i++){
+            if (electronicList[i] == null){
+                electronicList[i] = electronic;
+                break;
+            }
+        }
+        return electronic;
+    }
+
+
+    /*
+    * Q.전자제품 일련번호 productNo를 통해 인자로 주어진 일련번호에 해당하는 전자제품을 반환하는 함수를 작성하시오.*/
+    public Electronic findByProductNo(String productNo){
+        Electronic newElectronic = new Electronic(productNo);
+        for (Electronic electronic : electronicList) {
+            if (electronic.getProductNo().equals(productNo)) {
+                newElectronic = electronic;
+                break;
+            }
+        }
+        return newElectronic;
+
+    }
+
+    /*
+    * Q. 전자제품들 중 인자로 주어진 제조 회사를 찾아서 하나의 배열에 반환하는 함수를 작성하시오.*/
+
+    public Electronic[] groupByCompanyName(CompanyName companyName){
+        Electronic[] companyArray = new Electronic[arrSize];
+        int cnt = 0;
+        for (Electronic electronic : electronicList) {
+            if (electronic != null && electronic.getCompanyName().equals(companyName)) {
+                companyArray[cnt] = electronic;
+                cnt++;
+            }
+        }
+        return companyArray;
+    }
+
+    /*
+    * Q. 전자제품들 중 인자로 주어진 인증 방법을 찾아서 하나의 배열에 반환하는 함수를 작성하시오.*/
+    public Electronic[] groupByAuthMethod(AuthMethod authMethod){
+        Electronic[] authMethodArray = new Electronic[arrSize];
+//        int cnt = 0;
+//        for (Electronic electronic : electronicList){
+//            if (electronic.getAuthMethod() == null || electronic.getAuthMethod() == null) continue;
+//            for (AuthMethod method : electronic.getAuthMethod()){
+//                if(method.equals(authMethod)){
+//                    if (electronic.getAuthMethod() == null) continue;
+//                    authMethodArray[cnt] = electronic;
+//                    cnt++;
+//                    break;
+//                }
+//            }
+//        }
+
+        for (int i = 0; i < electronicList.length; i++) {
+            if (electronicList[i] == null) continue;
+            if (electronicList[i].getCompanyName() == null || electronicList[i].getAuthMethod().length == 0) continue;
+            for (int j = 0; j < electronicList[i].getAuthMethod().length; j++) {
+                if (electronicList[i].getAuthMethod()[j] == null) continue;
+                if (electronicList[i].getAuthMethod()[j] == authMethod) {
+                    authMethodArray[i] = electronicList[i];
+                    break;
+                }
+            }
+        }
+        return authMethodArray;
+    }
+
+    public Electronic[] getElectronicList() {
+        return electronicList;
+    }
+
+    public void setElectronicList(Electronic[] electronicList) {
+        this.electronicList = electronicList;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) return true;
+        if (o == null || getClass() != o.getClass()) return false;
+        Electronics that = (Electronics) o;
+        return Arrays.equals(electronicList, that.electronicList);
+    }
+
+
+    @Override
+    public int hashCode() {
+        int result = Objects.hash(arrSize);
+        result = 31 * result + Arrays.hashCode(electronicList);
+        return result;
+    }
+
+    @Override
+    public String toString() {
+        return "Electronics{" +
+                "arrSize=" + arrSize +
+                ", electronicList=" + Arrays.toString(electronicList) +
+                '}';
+    }
+
+}