diff --git a/src/me/day05/practice/Practice01/AuthMethod.java b/src/me/day05/practice/Practice01/AuthMethod.java
new file mode 100644
index 0000000..9f9d514
--- /dev/null
+++ b/src/me/day05/practice/Practice01/AuthMethod.java
@@ -0,0 +1,9 @@
+package me.day05.practice.Practice01;
+
+//본인인증 방법  — Enum형으로 정의
+public enum AuthMethod {
+    지문인증,
+    패턴인증,
+    핀인증,
+    얼굴인증
+}
diff --git a/src/me/day05/practice/Practice01/CompanyName.java b/src/me/day05/practice/Practice01/CompanyName.java
new file mode 100644
index 0000000..cb292c0
--- /dev/null
+++ b/src/me/day05/practice/Practice01/CompanyName.java
@@ -0,0 +1,8 @@
+package me.day05.practice.Practice01;
+
+//제조회사명 — Enum형으로 정의
+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..d57a1d9
--- /dev/null
+++ b/src/me/day05/practice/Practice01/Electronic.java
@@ -0,0 +1,104 @@
+package me.day05.practice.Practice01;
+
+import java.time.LocalDate;
+import java.time.format.DateTimeFormatter;
+import java.util.Arrays;
+import java.util.Objects;
+
+public class Electronic {
+    private String productNo;
+    private String modelName;
+    private CompanyName companyName;
+    private LocalDate dateOfMade;
+    private AuthMethod[] authMethod; // 본인인증 방법 — 배열로 정의
+
+    private static int orderNum = 0;
+
+    public Electronic(String modelName, CompanyName companyName, LocalDate dateOfMade, AuthMethod[] authMethod) {
+        orderNum++;
+        this.productNo = orderProductNo();
+        this.modelName = modelName;
+        this.companyName = companyName;
+        this.dateOfMade = dateOfMade;
+        this.authMethod = authMethod;
+    }
+
+
+    //ex. if 2023/03/30(now) then 230330 + 0001 (4자리 등록 순서) ⇒ 2303300001
+    private String orderProductNo() {
+        DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyMMdd");
+        String date = LocalDate.now().format(formatter);
+        String order_cnt = String.format("%04d", orderNum);
+        return date + order_cnt;
+    }
+
+
+    public String getProductNo() {
+        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;
+    }
+
+    public static void setOrderNum(int orderNum) {
+        Electronic.orderNum = orderNum;
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(productNo, modelName, companyName, dateOfMade, Arrays.hashCode(authMethod));
+    }
+
+    @Override
+    public boolean equals(Object obj) {
+        if (this == obj) return true;
+        if (obj == null || getClass() != obj.getClass()) return false;
+        Electronic that = (Electronic) obj;
+        return Objects.equals(productNo, that.productNo) &&
+                Objects.equals(modelName, that.modelName) &&
+                companyName == that.companyName &&
+                Objects.equals(dateOfMade, that.dateOfMade) &&
+                Arrays.equals(authMethod, that.authMethod);
+    }
+
+    @Override
+    public String toString() {
+        return "Electronic{" +
+                "productNo='" + productNo + '\'' +
+                ", modelName='" + modelName + '\'' +
+                ", companyName=" + companyName +
+                ", dateOfMade=" + dateOfMade +
+                ", authMethod=" + Arrays.toString(authMethod) +
+                '}';
+    }
+}
+
diff --git a/src/me/day05/practice/Practice01/Test.java b/src/me/day05/practice/Practice01/Test.java
new file mode 100644
index 0000000..8e22b05
--- /dev/null
+++ b/src/me/day05/practice/Practice01/Test.java
@@ -0,0 +1,24 @@
+package me.day05.practice.Practice01;
+
+import java.time.LocalDate;
+
+public class Test {
+    public static void main(String[] args) {
+        //checking electronic
+        Electronic device1 = new Electronic("iphone13", CompanyName.APPLE, LocalDate.of(2021, 9, 1), new AuthMethod[] {AuthMethod.얼굴인증});
+        Electronic device2 = new Electronic("iphone8", CompanyName.APPLE, LocalDate.of(2017, 9, 1), new AuthMethod[] {AuthMethod.지문인증});
+
+        System.out.println(device1);
+        System.out.println(device2);
+        /* 출력
+                Electronic{productNo='2304180001', modelName='iphone13', companyName=APPLE, dateOfMade=2021-09-01, authMethods=[얼굴인증]}
+                Electronic{productNo='2304180002', modelName='iphone8', companyName=APPLE, dateOfMade=2017-09-01, authMethods=[지문인증]}
+        */
+
+        User user1 = new User("abc", "1234", "010-1111-2222", "abc@efg.com", "010101", new String[] {"device2"});
+        System.out.println(user1);
+
+        //출력 Users{userId='abc', userPassword='1234', userPhoneNumber='010-1111-2222', userEmail='abc@efg.com', userBirthDate='010101', electronicDevices=[device2], registerTime=2023-04-18}
+
+    }
+}
diff --git a/src/me/day05/practice/Practice01/User.java b/src/me/day05/practice/Practice01/User.java
new file mode 100644
index 0000000..cf9d273
--- /dev/null
+++ b/src/me/day05/practice/Practice01/User.java
@@ -0,0 +1,120 @@
+package me.day05.practice.Practice01;
+
+import java.time.LocalDate;
+import java.util.Arrays;
+import java.util.Objects;
+
+public class User {
+    private String userId;
+    private String userPassword;
+    private String userPhoneNumber;
+    private String userEmail;
+    private String userBirthDate;
+    private String[] electronicDevices;
+    private LocalDate registerTime;
+
+    //객체 생성시 시스템 시간으로 자동 설정
+    public User() {
+        this.registerTime = LocalDate.now();
+    }
+
+    public User(String userId, String userPassword, String userPhoneNumber, String userEmail, String userBirthDate, String[] electronicDevices) {
+        this.userId = userId;
+        this.userPassword = userPassword;
+        this.userPhoneNumber = userPhoneNumber;
+        this.userEmail = userEmail;
+        this.userBirthDate = userBirthDate;
+        this.electronicDevices = electronicDevices;
+        this.registerTime = LocalDate.now();
+
+    }
+
+    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 String getUserBirthDate() {
+        return userBirthDate;
+    }
+
+    public void setUserBirthDate(String userBirthDate) {
+        this.userBirthDate = userBirthDate;
+    }
+
+    public String[] getElectronicDevices() {
+        return electronicDevices;
+    }
+
+    public void setElectronicDevices(String[] electronicDevices) {
+        this.electronicDevices = electronicDevices;
+    }
+
+    public LocalDate getRegisterTime() {
+        return registerTime;
+    }
+
+    public void setRegisterTime(LocalDate registerTime) {
+        this.registerTime = registerTime;
+    }
+
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(userId, userPassword, userPhoneNumber, userEmail, userBirthDate, electronicDevices);
+    }
+
+    @Override
+    public boolean equals(Object obj) {
+        if (this == obj) return true;
+        if (obj == null || getClass() != obj.getClass()) return false;
+        User user = (User) obj;
+        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);
+    }
+
+    @Override
+    public String toString() {
+        return "Users{" +
+                "userId='" + userId + '\'' +
+                ", userPassword='" + userPassword + '\'' +
+                ", userPhoneNumber='" + userPhoneNumber + '\'' +
+                ", userEmail='" + userEmail + '\'' +
+                ", userBirthDate='" + userBirthDate + '\'' +
+                ", electronicDevices=" + Arrays.toString(electronicDevices) +
+                ", registerTime=" + registerTime +
+                '}';
+    }
+}
+
diff --git a/src/me/day05/practice/Practice02/Users.java b/src/me/day05/practice/Practice02/Users.java
new file mode 100644
index 0000000..da427c4
--- /dev/null
+++ b/src/me/day05/practice/Practice02/Users.java
@@ -0,0 +1,69 @@
+package me.day05.practice.Practice02;
+import me.day05.practice.Practice01.User;
+
+import java.util.Arrays;
+
+public class Users {
+    private User[] userList;
+    private Users() {
+    }
+
+    private static Users instance = new Users();
+
+    //2-1 Users 클래스의 객체를 싱글톤으로 생성하는 함수를 작성
+    public static Users getInstance() {
+        if (instance == null) {
+            instance = new Users();
+        }
+        return instance;
+    }
+
+    public User[] getUserList() {
+        return userList;
+    }
+
+    public void setUserList(User[] userList) {
+        this.userList = userList;
+    }
+
+    //2-2 userId를 통해 인자로 주어진 회원번호에 해당하는 회원을 반환하는 함수를 작성
+    public User findByUserId(String userId) {
+        for (User user : userList) {
+            if (user.getUserId().equals(userId)) {
+                return user;
+            }
+        }
+        throw new IllegalArgumentException("Not found");
+    }
+
+    //2-3 인자로 주어진 회원 정보를 깊은 복사 (deepCopy) 하는 함수를 작성
+    public User copy(User original) {
+        User user_info = new User(
+                original.getUserId(),
+                original.getUserEmail(),
+                original.getUserPassword(),
+                original.getUserBirthDate(),
+                original.getUserPhoneNumber(),
+                original.getElectronicDevices()
+        );
+        return user_info;
+    }
+
+    @Override
+    public boolean equals(Object obj) {
+        if (this == obj) return true;
+        if (obj == null || getClass() != obj.getClass()) return false;
+        Users users = (Users) obj;
+        return Arrays.equals(userList, users.userList);
+    }
+
+    @Override
+    public int hashCode() {
+        return Arrays.hashCode(userList);
+    }
+
+    @Override
+    public String toString() {
+        return "{" + "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..2026e72
--- /dev/null
+++ b/src/me/day05/practice/Practice03/Electronics.java
@@ -0,0 +1,86 @@
+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.util.Arrays;
+import java.util.ArrayList;
+import java.util.List;
+
+public class Electronics {
+    private static Electronic[] electronicList;
+    private Electronics() {
+    }
+
+    private static Electronics instance;
+
+    //3-1 Electronics 클래스의 객체를 싱글톤으로 생성하는 함수를 작성
+    public static Electronics getInstance() {
+        if (instance == null) {
+            instance = new Electronics();
+        }
+        return instance;
+    }
+
+    public static Electronic[] getElectronicList() {
+        return electronicList;
+    }
+
+    public static void setElectronicList(Electronic[] electronicList) {
+        Electronics.electronicList = electronicList;
+    }
+
+    //3-2 productNo를 통해 인자로 주어진 일련번호에 해당하는 전자제품을 반환하는 함수를 작성
+    public Electronic findByProductNo(String productNo) {
+        for (Electronic electronic : electronicList) {
+            if (electronic.getProductNo().equals(productNo)) {
+                return electronic;
+            }
+        }
+        throw new IllegalArgumentException("Not found");
+    }
+
+    //3-3 제조 회사를 찾아서 하나의 배열에 반환하는 함수를 작성
+    public Electronic[] groupByCompanyName(CompanyName company) {
+        List<Electronic> electronics = new ArrayList<>();
+        for (Electronic electronic : electronicList) {
+            if (electronic.getCompanyName().equals(company)) {
+                electronics.add(electronic);
+            }
+        }
+
+        return electronics.toArray(new Electronic[electronics.size()]);
+    }
+
+
+    //3-4 주어진 인증 방법을 찾아서 하나의 배열에 반환하는 함수를 작성
+    public Electronic[] groupByAuthMethod(AuthMethod authMethod){
+        List<Electronic> groupAuthList = new ArrayList<>();
+        for (Electronic electronic : electronicList) {
+            if (electronic.getAuthMethod().equals(authMethod)) {
+                groupAuthList.add(electronic);
+            }
+        }
+        return groupAuthList.toArray((new Electronic[groupAuthList.size()]));
+    }
+
+
+    @Override
+    public boolean equals(Object obj) {
+        if (this == obj) return true;
+        if (obj == null || getClass() != obj.getClass()) return false;
+        Electronics electronics = (Electronics) obj;
+        return Arrays.equals(electronicList, electronics.electronicList);
+    }
+
+    @Override
+    public int hashCode() {
+        return Arrays.hashCode(electronicList);
+    }
+
+    @Override
+    public String toString() {
+        return "{" + "userList=" + Arrays.toString(electronicList) + "}";
+    }
+}
\ No newline at end of file