diff --git a/.gitignore b/.gitignore
new file mode 100644
index 000000000..7cb6b1c91
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,43 @@
+.gradle
+build/
+!gradle/wrapper/gradle-wrapper.jar
+!**/src/main/**/build/
+!**/src/test/**/build/
+
+### IntelliJ IDEA ###
+.idea/modules.xml
+.idea/jarRepositories.xml
+.idea/compiler.xml
+.idea/libraries/
+.idea
+*.iws
+*.iml
+*.ipr
+out/
+!**/src/main/**/out/
+!**/src/test/**/out/
+
+### Eclipse ###
+.apt_generated
+.classpath
+.factorypath
+.project
+.settings
+.springBeans
+.sts4-cache
+bin/
+!**/src/main/**/bin/
+!**/src/test/**/bin/
+
+### NetBeans ###
+/nbproject/private/
+/nbbuild/
+/dist/
+/nbdist/
+/.nb-gradle/
+
+### VS Code ###
+.vscode/
+
+### Mac OS ###
+.DS_Store
\ No newline at end of file
diff --git a/build.gradle b/build.gradle
new file mode 100644
index 000000000..668101a29
--- /dev/null
+++ b/build.gradle
@@ -0,0 +1,19 @@
+plugins {
+    id 'java'
+}
+
+group = 'com.sprint.mission'
+version = '1.0-SNAPSHOT'
+
+repositories {
+    mavenCentral()
+}
+
+dependencies {
+    testImplementation platform('org.junit:junit-bom:5.10.0')
+    testImplementation 'org.junit.jupiter:junit-jupiter'
+}
+
+test {
+    useJUnitPlatform()
+}
\ No newline at end of file
diff --git a/gradle/wrapper/gradle-wrapper.jar b/gradle/wrapper/gradle-wrapper.jar
new file mode 100644
index 000000000..249e5832f
Binary files /dev/null and b/gradle/wrapper/gradle-wrapper.jar differ
diff --git a/gradle/wrapper/gradle-wrapper.properties b/gradle/wrapper/gradle-wrapper.properties
new file mode 100644
index 000000000..f3afae7b7
--- /dev/null
+++ b/gradle/wrapper/gradle-wrapper.properties
@@ -0,0 +1,6 @@
+#Thu Apr 10 09:38:34 KST 2025
+distributionBase=GRADLE_USER_HOME
+distributionPath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-8.10-bin.zip
+zipStoreBase=GRADLE_USER_HOME
+zipStorePath=wrapper/dists
diff --git a/gradlew b/gradlew
new file mode 100644
index 000000000..1b6c78733
--- /dev/null
+++ b/gradlew
@@ -0,0 +1,234 @@
+#!/bin/sh
+
+#
+# Copyright © 2015-2021 the original authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+##############################################################################
+#
+#   Gradle start up script for POSIX generated by Gradle.
+#
+#   Important for running:
+#
+#   (1) You need a POSIX-compliant shell to run this script. If your /bin/sh is
+#       noncompliant, but you have some other compliant shell such as ksh or
+#       bash, then to run this script, type that shell name before the whole
+#       command line, like:
+#
+#           ksh Gradle
+#
+#       Busybox and similar reduced shells will NOT work, because this script
+#       requires all of these POSIX shell features:
+#         * functions;
+#         * expansions «$var», «${var}», «${var:-default}», «${var+SET}»,
+#           «${var#prefix}», «${var%suffix}», and «$( cmd )»;
+#         * compound commands having a testable exit status, especially «case»;
+#         * various built-in commands including «command», «set», and «ulimit».
+#
+#   Important for patching:
+#
+#   (2) This script targets any POSIX shell, so it avoids extensions provided
+#       by Bash, Ksh, etc; in particular arrays are avoided.
+#
+#       The "traditional" practice of packing multiple parameters into a
+#       space-separated string is a well documented source of bugs and security
+#       problems, so this is (mostly) avoided, by progressively accumulating
+#       options in "$@", and eventually passing that to Java.
+#
+#       Where the inherited environment variables (DEFAULT_JVM_OPTS, JAVA_OPTS,
+#       and GRADLE_OPTS) rely on word-splitting, this is performed explicitly;
+#       see the in-line comments for details.
+#
+#       There are tweaks for specific operating systems such as AIX, CygWin,
+#       Darwin, MinGW, and NonStop.
+#
+#   (3) This script is generated from the Groovy template
+#       https://github.com/gradle/gradle/blob/master/subprojects/plugins/src/main/resources/org/gradle/api/internal/plugins/unixStartScript.txt
+#       within the Gradle project.
+#
+#       You can find Gradle at https://github.com/gradle/gradle/.
+#
+##############################################################################
+
+# Attempt to set APP_HOME
+
+# Resolve links: $0 may be a link
+app_path=$0
+
+# Need this for daisy-chained symlinks.
+while
+    APP_HOME=${app_path%"${app_path##*/}"}  # leaves a trailing /; empty if no leading path
+    [ -h "$app_path" ]
+do
+    ls=$( ls -ld "$app_path" )
+    link=${ls#*' -> '}
+    case $link in             #(
+      /*)   app_path=$link ;; #(
+      *)    app_path=$APP_HOME$link ;;
+    esac
+done
+
+APP_HOME=$( cd "${APP_HOME:-./}" && pwd -P ) || exit
+
+APP_NAME="Gradle"
+APP_BASE_NAME=${0##*/}
+
+# Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+DEFAULT_JVM_OPTS='"-Xmx64m" "-Xms64m"'
+
+# Use the maximum available, or set MAX_FD != -1 to use that value.
+MAX_FD=maximum
+
+warn () {
+    echo "$*"
+} >&2
+
+die () {
+    echo
+    echo "$*"
+    echo
+    exit 1
+} >&2
+
+# OS specific support (must be 'true' or 'false').
+cygwin=false
+msys=false
+darwin=false
+nonstop=false
+case "$( uname )" in                #(
+  CYGWIN* )         cygwin=true  ;; #(
+  Darwin* )         darwin=true  ;; #(
+  MSYS* | MINGW* )  msys=true    ;; #(
+  NONSTOP* )        nonstop=true ;;
+esac
+
+CLASSPATH=$APP_HOME/gradle/wrapper/gradle-wrapper.jar
+
+
+# Determine the Java command to use to start the JVM.
+if [ -n "$JAVA_HOME" ] ; then
+    if [ -x "$JAVA_HOME/jre/sh/java" ] ; then
+        # IBM's JDK on AIX uses strange locations for the executables
+        JAVACMD=$JAVA_HOME/jre/sh/java
+    else
+        JAVACMD=$JAVA_HOME/bin/java
+    fi
+    if [ ! -x "$JAVACMD" ] ; then
+        die "ERROR: JAVA_HOME is set to an invalid directory: $JAVA_HOME
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+    fi
+else
+    JAVACMD=java
+    which java >/dev/null 2>&1 || die "ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+fi
+
+# Increase the maximum file descriptors if we can.
+if ! "$cygwin" && ! "$darwin" && ! "$nonstop" ; then
+    case $MAX_FD in #(
+      max*)
+        MAX_FD=$( ulimit -H -n ) ||
+            warn "Could not query maximum file descriptor limit"
+    esac
+    case $MAX_FD in  #(
+      '' | soft) :;; #(
+      *)
+        ulimit -n "$MAX_FD" ||
+            warn "Could not set maximum file descriptor limit to $MAX_FD"
+    esac
+fi
+
+# Collect all arguments for the java command, stacking in reverse order:
+#   * args from the command line
+#   * the main class name
+#   * -classpath
+#   * -D...appname settings
+#   * --module-path (only if needed)
+#   * DEFAULT_JVM_OPTS, JAVA_OPTS, and GRADLE_OPTS environment variables.
+
+# For Cygwin or MSYS, switch paths to Windows format before running java
+if "$cygwin" || "$msys" ; then
+    APP_HOME=$( cygpath --path --mixed "$APP_HOME" )
+    CLASSPATH=$( cygpath --path --mixed "$CLASSPATH" )
+
+    JAVACMD=$( cygpath --unix "$JAVACMD" )
+
+    # Now convert the arguments - kludge to limit ourselves to /bin/sh
+    for arg do
+        if
+            case $arg in                                #(
+              -*)   false ;;                            # don't mess with options #(
+              /?*)  t=${arg#/} t=/${t%%/*}              # looks like a POSIX filepath
+                    [ -e "$t" ] ;;                      #(
+              *)    false ;;
+            esac
+        then
+            arg=$( cygpath --path --ignore --mixed "$arg" )
+        fi
+        # Roll the args list around exactly as many times as the number of
+        # args, so each arg winds up back in the position where it started, but
+        # possibly modified.
+        #
+        # NB: a `for` loop captures its iteration list before it begins, so
+        # changing the positional parameters here affects neither the number of
+        # iterations, nor the values presented in `arg`.
+        shift                   # remove old arg
+        set -- "$@" "$arg"      # push replacement arg
+    done
+fi
+
+# Collect all arguments for the java command;
+#   * $DEFAULT_JVM_OPTS, $JAVA_OPTS, and $GRADLE_OPTS can contain fragments of
+#     shell script including quotes and variable substitutions, so put them in
+#     double quotes to make sure that they get re-expanded; and
+#   * put everything else in single quotes, so that it's not re-expanded.
+
+set -- \
+        "-Dorg.gradle.appname=$APP_BASE_NAME" \
+        -classpath "$CLASSPATH" \
+        org.gradle.wrapper.GradleWrapperMain \
+        "$@"
+
+# Use "xargs" to parse quoted args.
+#
+# With -n1 it outputs one arg per line, with the quotes and backslashes removed.
+#
+# In Bash we could simply go:
+#
+#   readarray ARGS < <( xargs -n1 <<<"$var" ) &&
+#   set -- "${ARGS[@]}" "$@"
+#
+# but POSIX shell has neither arrays nor command substitution, so instead we
+# post-process each arg (as a line of input to sed) to backslash-escape any
+# character that might be a shell metacharacter, then use eval to reverse
+# that process (while maintaining the separation between arguments), and wrap
+# the whole thing up as a single "set" statement.
+#
+# This will of course break if any of these variables contains a newline or
+# an unmatched quote.
+#
+
+eval "set -- $(
+        printf '%s\n' "$DEFAULT_JVM_OPTS $JAVA_OPTS $GRADLE_OPTS" |
+        xargs -n1 |
+        sed ' s~[^-[:alnum:]+,./:=@_]~\\&~g; ' |
+        tr '\n' ' '
+    )" '"$@"'
+
+exec "$JAVACMD" "$@"
diff --git a/gradlew.bat b/gradlew.bat
new file mode 100644
index 000000000..107acd32c
--- /dev/null
+++ b/gradlew.bat
@@ -0,0 +1,89 @@
+@rem
+@rem Copyright 2015 the original author or authors.
+@rem
+@rem Licensed under the Apache License, Version 2.0 (the "License");
+@rem you may not use this file except in compliance with the License.
+@rem You may obtain a copy of the License at
+@rem
+@rem      https://www.apache.org/licenses/LICENSE-2.0
+@rem
+@rem Unless required by applicable law or agreed to in writing, software
+@rem distributed under the License is distributed on an "AS IS" BASIS,
+@rem WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+@rem See the License for the specific language governing permissions and
+@rem limitations under the License.
+@rem
+
+@if "%DEBUG%" == "" @echo off
+@rem ##########################################################################
+@rem
+@rem  Gradle startup script for Windows
+@rem
+@rem ##########################################################################
+
+@rem Set local scope for the variables with windows NT shell
+if "%OS%"=="Windows_NT" setlocal
+
+set DIRNAME=%~dp0
+if "%DIRNAME%" == "" set DIRNAME=.
+set APP_BASE_NAME=%~n0
+set APP_HOME=%DIRNAME%
+
+@rem Resolve any "." and ".." in APP_HOME to make it shorter.
+for %%i in ("%APP_HOME%") do set APP_HOME=%%~fi
+
+@rem Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+set DEFAULT_JVM_OPTS="-Xmx64m" "-Xms64m"
+
+@rem Find java.exe
+if defined JAVA_HOME goto findJavaFromJavaHome
+
+set JAVA_EXE=java.exe
+%JAVA_EXE% -version >NUL 2>&1
+if "%ERRORLEVEL%" == "0" goto execute
+
+echo.
+echo ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+echo.
+echo Please set the JAVA_HOME variable in your environment to match the
+echo location of your Java installation.
+
+goto fail
+
+:findJavaFromJavaHome
+set JAVA_HOME=%JAVA_HOME:"=%
+set JAVA_EXE=%JAVA_HOME%/bin/java.exe
+
+if exist "%JAVA_EXE%" goto execute
+
+echo.
+echo ERROR: JAVA_HOME is set to an invalid directory: %JAVA_HOME%
+echo.
+echo Please set the JAVA_HOME variable in your environment to match the
+echo location of your Java installation.
+
+goto fail
+
+:execute
+@rem Setup the command line
+
+set CLASSPATH=%APP_HOME%\gradle\wrapper\gradle-wrapper.jar
+
+
+@rem Execute Gradle
+"%JAVA_EXE%" %DEFAULT_JVM_OPTS% %JAVA_OPTS% %GRADLE_OPTS% "-Dorg.gradle.appname=%APP_BASE_NAME%" -classpath "%CLASSPATH%" org.gradle.wrapper.GradleWrapperMain %*
+
+:end
+@rem End local scope for the variables with windows NT shell
+if "%ERRORLEVEL%"=="0" goto mainEnd
+
+:fail
+rem Set variable GRADLE_EXIT_CONSOLE if you need the _script_ return code instead of
+rem the _cmd.exe /c_ return code!
+if  not "" == "%GRADLE_EXIT_CONSOLE%" exit 1
+exit /b 1
+
+:mainEnd
+if "%OS%"=="Windows_NT" endlocal
+
+:omega
diff --git a/settings.gradle b/settings.gradle
new file mode 100644
index 000000000..79373e364
--- /dev/null
+++ b/settings.gradle
@@ -0,0 +1,2 @@
+rootProject.name = '3-sprint-mission'
+
diff --git a/src/main/java/com/sprint/mission/discodeit/JavaApplication.java b/src/main/java/com/sprint/mission/discodeit/JavaApplication.java
new file mode 100644
index 000000000..9e5ab6fe8
--- /dev/null
+++ b/src/main/java/com/sprint/mission/discodeit/JavaApplication.java
@@ -0,0 +1,64 @@
+package com.sprint.mission.discodeit;
+
+import com.sprint.mission.discodeit.entity.Channel;
+import com.sprint.mission.discodeit.entity.Message;
+import com.sprint.mission.discodeit.entity.User;
+import com.sprint.mission.discodeit.service.ChannelService;
+import com.sprint.mission.discodeit.service.MessageService;
+import com.sprint.mission.discodeit.service.UserService;
+import com.sprint.mission.discodeit.service.jcf.JCFChannelService;
+import com.sprint.mission.discodeit.service.jcf.JCFMessageService;
+import com.sprint.mission.discodeit.service.jcf.JCFUserService;
+
+import java.util.UUID;
+
+public class JavaApplication {
+    public static void main(String[] args) {
+        // 서비스 생성
+        UserService userService = new JCFUserService();
+        ChannelService channelService = new JCFChannelService();
+        MessageService messageService = new JCFMessageService();
+
+        // User 등록
+        User user1 = new User("Alice", 20, "alice@gmail.com");
+        userService.createUser(user1);
+
+        // Channel 등록
+        Channel channel1 = new Channel("general", user1);
+        channelService.createChannel(channel1);
+
+        // Message 등록
+        Message message1 = new Message(user1, channel1, "Hello, world!");
+        messageService.createMessage(message1);
+
+        // 조회
+        System.out.println("User 조회: " + userService.readUser(user1.getId()));
+        System.out.println("Channel 조회: " + channelService.readChannel(channel1.getId()));
+        System.out.println("Message 조회: " + messageService.readMessage(message1.getId()));
+
+        // 수정
+        userService.updateUser(user1.getId(), "Bob");
+        channelService.updateChannel(channel1.getId(), "random");
+        messageService.updateMessage(message1.getId(), "Updated message");
+
+        // 수정된 데이터 확인
+        System.out.println("수정된 User: " + userService.readUser(user1.getId()));
+        System.out.println("수정된 Channel: " + channelService.readChannel(channel1.getId()));
+        System.out.println("수정된 Message: " + messageService.readMessage(message1.getId()));
+
+        // 삭제
+        userService.deleteUser(user1.getId());
+        channelService.deleteChannel(channel1.getId());
+        messageService.deleteMessage(message1.getId());
+
+        // 삭제된 데이터 조회 시도
+        System.out.println("삭제 후 User: " + userService.readUser(user1.getId()));
+        System.out.println("삭제 후 Channel: " + channelService.readChannel(channel1.getId()));
+        System.out.println("삭제 후 Message: " + messageService.readMessage(message1.getId()));
+
+        // 전체 조회
+        System.out.println("전체 Users: " + userService.readAllUsers());
+        System.out.println("전체 Channels: " + channelService.readAllChannels());
+        System.out.println("전체 Messages: " + messageService.readAllMessages());
+    }
+}
diff --git a/src/main/java/com/sprint/mission/discodeit/entity/Base.java b/src/main/java/com/sprint/mission/discodeit/entity/Base.java
new file mode 100644
index 000000000..021f2d131
--- /dev/null
+++ b/src/main/java/com/sprint/mission/discodeit/entity/Base.java
@@ -0,0 +1,35 @@
+package com.sprint.mission.discodeit.entity;
+
+import java.util.UUID;
+
+public class Base {
+    private UUID id; // Channel CRUD를 위해 UUID가 필요한가?
+    // @CreatedDate 는 Spring 전용
+    private Long createdAt;
+    // @CreatedDate
+    private Long updatedAt;
+
+    public Base() {
+    }
+
+    public Base(UUID id, Long createdAt, Long updatedAt) {
+        this.id = UUID.randomUUID();
+        this.createdAt = System.currentTimeMillis();
+        this.updatedAt = createdAt;
+    }
+
+    public UUID getId() { // 이게 왜 이렇게 문제가 많이 일어나지
+        return id;
+    }
+
+    public Long getCreatedAt() {
+        return createdAt;
+    }
+
+    public Long getUpdatedAt() {
+        return updatedAt;
+    }
+
+    public void updateUpdatedAt() {
+        this.updatedAt = System.currentTimeMillis();
+}
diff --git a/src/main/java/com/sprint/mission/discodeit/entity/Channel.java b/src/main/java/com/sprint/mission/discodeit/entity/Channel.java
new file mode 100644
index 000000000..3d8fb4a20
--- /dev/null
+++ b/src/main/java/com/sprint/mission/discodeit/entity/Channel.java
@@ -0,0 +1,55 @@
+package com.sprint.mission.discodeit.entity;
+
+import java.util.*;
+import java.util.UUID;
+
+public class Channel extends Base {
+    private String channelName;
+    private List<User> members = new ArrayList<>(); // Channel List안에 members List를 넣고 member와 message로 이루어진 LinkedList를 만들고 싶음
+    private UUID channelId;
+
+    public Channel(String channelName, User user) {
+        super();
+        this.channelName = channelName;
+        this.members.add(user);
+    }
+
+
+    // Gettter Method
+
+    public String getChannelName() {
+        return this.channelName;
+    }
+
+    public List<User> getMembers() {
+        return this.members;
+    }
+
+
+    // Update Method
+
+    public void updateChannelId(UUID channelId) {
+        this.channelId = super.getId();
+        super.updateUpdatedAt();
+    }
+
+    public void updateChannelName(String channelName) {
+        this.channelName = channelName;
+        super.updateUpdatedAt();
+    }
+
+    public void updateMembers(List<User> members) {
+        this.members = new ArrayList<>(members);
+        super.updateUpdatedAt();
+    }
+
+    @Override
+    public String toString() {
+        return "Channel{" +
+                "name='" + getChannelName() + '\'' +
+                ", channelId='" + getId() + '\'' +
+                ", createdAt='" + getCreatedAt() + '\'' +
+                ", updatedAt='" + getUpdatedAt() + '\'' +
+                '}';
+    }
+}
\ No newline at end of file
diff --git a/src/main/java/com/sprint/mission/discodeit/entity/Message.java b/src/main/java/com/sprint/mission/discodeit/entity/Message.java
new file mode 100644
index 000000000..2d66676eb
--- /dev/null
+++ b/src/main/java/com/sprint/mission/discodeit/entity/Message.java
@@ -0,0 +1,57 @@
+package com.sprint.mission.discodeit.entity;
+
+
+import java.util.UUID;
+
+public class Message extends Base {
+    private User user;
+    private Channel channel; // 이걸 Channel 클래스와 어떻게 연결시키지
+    private String content; // message는 결국 HashSet이야
+
+    public Message(User user, Channel channel, String content) {
+        super();
+        this.user = user;
+        this.channel = channel;
+        this.content = content;
+    }
+
+
+    // Getter Methods
+
+    public User getUser() { return user; }
+
+    public Channel getChannel() { return channel; }
+
+    public String getContent() {
+        return content;
+    }
+
+
+    // Update Method
+
+    public void updateUser(UUID id) {
+        this.user = super.getId();
+        super.updateUpdatedAt();
+    }
+
+    public void updateChannel(Channel channel) {
+        this.channel = channel;
+        super.updateUpdatedAt();
+    }
+
+    public void updateContent(String message) {
+        this.content = content;
+        super.updateUpdatedAt();
+    }
+
+    @Override
+    public String toString() {
+        return "Message{" +
+                "message='" + getContent() + '\'' +
+                ", user='" + getUser().getName() + '\'' +
+                ", channel='" + getChannel().getChannelName() + '\'' +
+                ", id='" + getId() + '\'' +
+                ", createdAt='" + getCreatedAt() + '\'' +
+                ", updatedAt='" + getUpdatedAt() + '\'' +
+                '}';
+}
diff --git a/src/main/java/com/sprint/mission/discodeit/entity/User.java b/src/main/java/com/sprint/mission/discodeit/entity/User.java
new file mode 100644
index 000000000..be657c8c5
--- /dev/null
+++ b/src/main/java/com/sprint/mission/discodeit/entity/User.java
@@ -0,0 +1,54 @@
+package com.sprint.mission.discodeit.entity;
+
+
+public class User extends Base {
+    private int age;
+    private String name;
+    private String email;
+
+    public User(String name, int age, String email) {
+        super();
+        this.age = age;
+        this.name = name;
+        this.email = email;
+    }
+
+
+    // Getter Method
+
+    public int getAge() { return age; }
+
+    public String getName() { return name; }
+
+    public String getEmail() { return email; }
+
+
+    // Update Method
+
+    public void updateAge(int age) {
+        this.age = age;
+        super.updateUpdatedAt();
+    }
+
+    public void updateName(String name) {
+        this.name = name;
+        super.updateUpdatedAt();
+    }
+
+    public void updateEmail(String email) {
+        this.email = email;
+        super.updateUpdatedAt();
+    }
+
+    @Override
+    public String toString() {
+        return "User{" +
+                "id=" + getId() +
+                ", name='" + getName() + '\'' +
+                ", age=" + getAge() +
+                ", email='" + getEmail() + '\'' +
+                ", createdAt='" + getCreatedAt() + '\'' +
+                ", updatedAt='" + getUpdatedAt() + '\'' +
+                '}';
+    }
+}
diff --git a/src/main/java/com/sprint/mission/discodeit/service/ChannelService.java b/src/main/java/com/sprint/mission/discodeit/service/ChannelService.java
new file mode 100644
index 000000000..1ca794208
--- /dev/null
+++ b/src/main/java/com/sprint/mission/discodeit/service/ChannelService.java
@@ -0,0 +1,14 @@
+package com.sprint.mission.discodeit.service;
+
+import com.sprint.mission.discodeit.entity.Channel;
+
+import java.util.List;
+import java.util.UUID;
+
+public interface ChannelService {
+    Channel createChannel(Channel channel); // C
+    Channel readChannel(UUID id); // R
+    List<Channel> readAllChannels();
+    void updateChannel(UUID id, String newName); // U
+    void deleteChannel(UUID id); // D
+}
diff --git a/src/main/java/com/sprint/mission/discodeit/service/MessageService.java b/src/main/java/com/sprint/mission/discodeit/service/MessageService.java
new file mode 100644
index 000000000..de0d39d43
--- /dev/null
+++ b/src/main/java/com/sprint/mission/discodeit/service/MessageService.java
@@ -0,0 +1,15 @@
+package com.sprint.mission.discodeit.service;
+
+import com.sprint.mission.discodeit.entity.Message;
+
+import java.util.List;
+import java.util.UUID;
+
+public interface MessageService {
+    void createMessage(Message message); // C
+    Message readMessage(UUID id); // R
+    List<Message> readAllMessages();
+    List<Message> readMessagesByChannelId(UUID channelId);
+    Message updateMessage(UUID id, String newMessage); // U
+    void deleteMessage(UUID id); // D
+}
diff --git a/src/main/java/com/sprint/mission/discodeit/service/UserService.java b/src/main/java/com/sprint/mission/discodeit/service/UserService.java
new file mode 100644
index 000000000..586245082
--- /dev/null
+++ b/src/main/java/com/sprint/mission/discodeit/service/UserService.java
@@ -0,0 +1,15 @@
+package com.sprint.mission.discodeit.service;
+
+
+import com.sprint.mission.discodeit.entity.User;
+
+import java.util.List;
+import java.util.UUID;
+
+public interface UserService {
+    void createUser(User user); // C
+    User readUser(UUID id); // R
+    List<User> readAllUsers();
+    void updateUser(UUID id, String newName); // U
+    void deleteUser(UUID id); // D
+}
diff --git a/src/main/java/com/sprint/mission/discodeit/service/jcf/JCFChannelService.java b/src/main/java/com/sprint/mission/discodeit/service/jcf/JCFChannelService.java
new file mode 100644
index 000000000..0b8c0df88
--- /dev/null
+++ b/src/main/java/com/sprint/mission/discodeit/service/jcf/JCFChannelService.java
@@ -0,0 +1,47 @@
+package com.sprint.mission.discodeit.service.jcf;
+
+import com.sprint.mission.discodeit.entity.Channel;
+import com.sprint.mission.discodeit.entity.User;
+import com.sprint.mission.discodeit.service.ChannelService;
+
+import java.util.*;
+
+public class JCFChannelService implements ChannelService {
+    private final Map<UUID, Channel> data; // Channel 데아터를 저장하는 필드
+
+    public JCFChannelService() { this.data = new HashMap<>(); } // 기본 생성자
+
+    @Override
+    public Channel createChannel(Channel channel) {
+        UUID channelId = channel.getId();
+        data.put(channelId, channel);
+        return channel; //
+    }
+
+    @Override
+    public Channel readChannel(UUID id) {
+        return data.get(id);
+    }
+
+    @Override
+    public List<Channel> readAllChannels() {
+        return new ArrayList<>(data.values());
+    };
+
+    @Override
+    public void updateChannel(UUID id, String newName) { // U
+        Channel channel = data.get(id);
+        if (channel != null) {
+            channel.updateChannelName(newName);
+            System.out.println("이름을 " + newName + "으로 수정했습니다.");
+        } else {
+            System.out.println("해당 사용자가 존재하지 않습니다.");
+        }
+    } // U
+
+    @Override
+    public void deleteChannel(UUID id) { // D
+        Channel channel = data.get(id);
+        data.remove(channel.getId()); // ID를 불러와서 없앰
+    };
+}
diff --git a/src/main/java/com/sprint/mission/discodeit/service/jcf/JCFMessageService.java b/src/main/java/com/sprint/mission/discodeit/service/jcf/JCFMessageService.java
new file mode 100644
index 000000000..6f040ea22
--- /dev/null
+++ b/src/main/java/com/sprint/mission/discodeit/service/jcf/JCFMessageService.java
@@ -0,0 +1,64 @@
+package com.sprint.mission.discodeit.service.jcf;
+
+import com.sprint.mission.discodeit.entity.Message;
+import com.sprint.mission.discodeit.service.MessageService;
+
+import java.util.*;
+import java.util.stream.Collectors;
+
+public class JCFMessageService implements MessageService { // 왜 오류가 뜨는지도 모르겠음 ㅠㅠ 그냥 안돼 그냥 안돼 그냥 안돼
+    private final Map<UUID, Message> data = new HashMap<>();;
+
+    public JCFMessageService() {} // 문제가 해결이 안돼 ㅠㅠ
+
+    @Override
+    public void createMessage(Message message) {
+        // 조건문으로 message를 받게 해야 하나? 그냥 보내면 받아야 하잖아
+        this.data.put(message.getId(), message);
+    }
+
+    @Override
+    public Message readMessage(UUID id) { // Q1. 왜 abstract 선언해야해? String content를 불러와야 하나?
+        for (Message msg : data) {
+            if (msg.getId().equals(id)) {
+                return msg;
+            }
+        }
+        return null;
+    }
+
+    @Override
+    public List<Message> readMessagesByChannelId(UUID channelId) {
+        return data.values().stream()
+                .filter(message -> message.getChannel().getId().equals(channelId))
+                .collect(Collectors.toList());
+    }
+
+
+    @Override
+    public List<Message> readAllMessages() {
+        return new ArrayList<>(data.values()); }
+
+    }
+    @Override
+    public Message updateMessage(UUID existId, String newContent) { // 왜 data를 못 받지?
+        Message existContent = data.get(existId); // 해당 id에 맞는 message 가져옴
+
+
+        if (existContent == null) {
+            return null; // 해당 id를 가진 existContent 없음
+        }
+
+        if (newContent != null && !newContent.isBlank()) {
+            existContent.updateContent(newContent);
+            data.put(existId, existContent); // 이게 필요해?
+        }
+
+        return data.get(existId);
+    }
+
+    @Override
+    public void deleteMessage(UUID id) {
+        this.data.remove(id);
+    }
+}
diff --git a/src/main/java/com/sprint/mission/discodeit/service/jcf/JCFUserService.java b/src/main/java/com/sprint/mission/discodeit/service/jcf/JCFUserService.java
new file mode 100644
index 000000000..45fbaa1d7
--- /dev/null
+++ b/src/main/java/com/sprint/mission/discodeit/service/jcf/JCFUserService.java
@@ -0,0 +1,47 @@
+package com.sprint.mission.discodeit.service.jcf;
+
+import com.sprint.mission.discodeit.entity.User;
+import com.sprint.mission.discodeit.service.UserService;
+
+import java.util.*;
+
+public class JCFUserService implements UserService { // 왜 abstract를 해야만 하는가?
+    private final HashMap<UUID, User> data;
+
+
+    public JCFUserService() {
+        this.data = new HashMap<>(); // HashMap이 UUID로 검색 용이
+    }
+
+    @Override
+    public void createUser(User user) { // C
+        data.put(user.getId(), user); // ID랑 user 저장
+    }
+
+    @Override
+    public User readUser(UUID id) {
+        return data.get(id);
+    } // R
+
+    @Override
+    public List<User> readAllUsers() {
+        return new ArrayList<>(data.values());
+    }; // R 전체 조회
+
+    @Override
+    public void updateUser(UUID id, String newName) { // U
+        User user = data.get(id);
+        if (user != null) {
+            user.updateName(newName);
+            System.out.println("이름을 " + newName + "으로 수정했습니다.");
+        } else {
+            System.out.println("해당 사용자가 존재하지 않습니다.");
+        }
+    };
+
+    @Override
+    public void deleteUser(UUID id) { // D
+        User user = data.get(id);
+        data.remove(user.getId()); // ID를 불러와서 없앰
+    };
+}
diff --git "a/\357\200\233\357\200\233\357\200\233f" "b/\357\200\233\357\200\233\357\200\233f"
new file mode 100644
index 000000000..480e6a064
--- /dev/null
+++ "b/\357\200\233\357\200\233\357\200\233f"
@@ -0,0 +1,24 @@
+diff.astextplain.textconv=astextplain
+filter.lfs.clean=git-lfs clean -- %f
+filter.lfs.smudge=git-lfs smudge -- %f
+filter.lfs.process=git-lfs filter-process
+filter.lfs.required=true
+http.sslbackend=openssl
+http.sslcainfo=C:/Program Files/Git/mingw64/etc/ssl/certs/ca-bundle.crt
+core.autocrlf=true
+core.fscache=true
+core.symlinks=false
+pull.rebase=false
+credential.helper=manager
+credential.https://dev.azure.com.usehttppath=true
+init.defaultbranch=master
+core.repositoryformatversion=0
+core.filemode=false
+core.bare=false
+core.logallrefupdates=true
+core.symlinks=false
+core.ignorecase=true
+remote.origin.url=https://github.com/codeit-bootcamp-spring/3-sprint-mission.git
+remote.origin.fetch=+refs/heads/임정현:refs/remotes/origin/임정현
+branch.임정현.remote=origin
+branch.임정현.merge=refs/heads/임정현