diff --git a/README.md b/README.md
index 8d7e8aee..11e05b90 100644
--- a/README.md
+++ b/README.md
@@ -1 +1,31 @@
-# java-baseball-precourse
\ No newline at end of file
+# java-baseball-precourse
+* Utilty Class
+    * 난수 생성 함수
+        * digit 범위의 3가지 난수를 중복되지 않을 때까지 뽑음.
+        * 난수 생성 시에는 Math.random() 사용
+        * 3자리 난수를 int[]로 반환
+    * 입력 받는 함수
+        * Scanner()를 사용해서 사용자 입력을 String으로 받고 반환.
+    * 입력값 유효성 검사 함수 1
+        * 파라미터로 String을 받음
+        * 길이가 3이 아닌 경우 throw
+        * 입력이 digit의 조합이 아닌 경우 throw
+        * 입력 digit이 중복되는 경우 throw
+        * 입력을 int[]로 반환
+    * strike 판정 함수
+        * 각 자릿수를 비교해서 strike 개수를 int로 반환
+    * ball 판정 함수
+        * 다른 자릿수를 비교하여 ball 개수를 int로 반환
+        * 난수도, 입력값도 중복이 없다고 가정했으므로 로직은 유효
+    * 출력문 반환 함수
+        * 파라미터로 strike 개수와 ball 개수를 받아 모두 0이면 "낫싱" 반환
+        * ball 개수가 0이 아니면 (ball 개수) + "볼 "을 저장, 0이라면 빈 문자열을 저장
+        * strike 개수가 0이 아니면 위에서 저장된 문자열에 (strike 개수) + "스트라이크"를 붙여서 반환, 0이라면 위에서 저장한 문자열만 반환
+    * 종료 후 출력 함수
+        * 파라미터로 strike 개수를 받아 3이 아니면 빈 문자열 반환
+        * 3이라면 안내문 출력 및 입력 받는 함수를 호출하여 입력 받기
+    * 입력값 유효성 검사 함수 2
+        * 파라미터로 String과 strike 개수를 받음
+        * strike 개수가 3이 아니면 true 반환
+        * "1"인 경우 true 반환
+        * "2"인 경우 false 반환
diff --git a/src/main/java/Application.java b/src/main/java/Application.java
new file mode 100644
index 00000000..981f0b47
--- /dev/null
+++ b/src/main/java/Application.java
@@ -0,0 +1,51 @@
+public class Application {
+
+    public static void main(String[] args) {
+        boolean continueFlag = true;
+        boolean makeFlag = true;
+        int[] randomNumbers = Utility.makeRandomNumbers();
+        int[] userNumbers;
+
+        while (continueFlag) {
+            if (makeFlag) {
+                makeFlag = false;
+                randomNumbers = Utility.makeRandomNumbers();
+            }
+
+            System.out.print("숫자를 입력해 주세요 : ");
+            String userString = Utility.getUserString();
+
+            try {
+                Utility.checkStringLength(userString);
+                Utility.checkStringDistinct(userString);
+                Utility.checkStringDigit(userString);
+            } catch (IllegalArgumentException e) {
+                System.out.print("올바르지 않은 입력입니다. ");
+                break;
+            }
+
+            userNumbers = Utility.stringToIntArray(userString);
+
+            int strike = Utility.strikeCount(randomNumbers, userNumbers);
+            int ball = Utility.ballCount(randomNumbers, userNumbers);
+
+            System.out.println(Utility.getStrikeBall(strike, ball));
+
+            Utility.printEndMessage(strike);
+
+            if (strike == 3) {
+                userString = Utility.getUserString();
+                makeFlag = true;
+            }
+
+            try {
+                continueFlag = Utility.checkKeepGoing(userString, strike);
+            } catch (IllegalArgumentException e) {
+                System.out.print("올바르지 않은 입력입니다. ");
+                break;
+            }
+        }
+
+        System.out.println("애플리케이션을 종료합니다.");
+    }
+}
diff --git a/src/main/java/Utility.java b/src/main/java/Utility.java
new file mode 100644
index 00000000..7fe55eee
--- /dev/null
+++ b/src/main/java/Utility.java
@@ -0,0 +1,133 @@
+import java.util.HashSet;
+import java.util.Scanner;
+
+public class Utility {
+
+    private Utility() {
+    }
+
+    public static int[] makeRandomNumbers() {
+        boolean[] flags = new boolean[10];
+        int[] randomNumbers = new int[3];
+        int count = 0;
+
+        while (count < 3) {
+            int temp = (int) (Math.random() * 9) + 1;
+            if (flags[temp]) {
+                continue;
+            } else {
+                randomNumbers[count] = temp;
+                flags[temp] = true;
+                count += 1;
+            }
+        }
+
+        return randomNumbers;
+    }
+
+    public static String getUserString() {
+        Scanner sc = new Scanner(System.in);
+        String userString = sc.nextLine();
+
+        return userString;
+    }
+
+    public static void checkStringLength(String userString) {
+        if (userString.length() != 3) {
+            throw new IllegalArgumentException();
+        }
+    }
+
+    public static void checkStringDistinct(String userString) {
+        HashSet<Character> tempSet = new HashSet<>();
+
+        for (int i = 0; i < userString.length(); i++) {
+            tempSet.add(userString.charAt(i));
+        }
+
+        if (tempSet.size() != userString.length()) {
+            throw new IllegalArgumentException();
+        }
+    }
+
+    public static void checkStringDigit(String userString) {
+        for (int i = 0; i < userString.length(); i++) {
+            int temp = (int) userString.charAt(i) - (int) '0';
+            if (temp < 1 || temp > 9) {
+                throw new IllegalArgumentException();
+            }
+        }
+    }
+
+    public static int[] stringToIntArray(String userString) {
+        int[] userNumbers = new int[3];
+
+        for (int i = 0; i < 3; i++) {
+            int temp = (int) userString.charAt(i) - (int) '0';
+            userNumbers[i] = temp;
+        }
+
+        return userNumbers;
+    }
+
+    public static int strikeCount(int[] randomNumbers, int[] userNumbers) {
+        int strike = 0;
+
+        for (int i = 0; i < 3; i++) {
+            if (randomNumbers[i] == userNumbers[i]) {
+                strike += 1;
+            }
+        }
+
+        return strike;
+    }
+
+    public static int ballCount(int[] randomNumbers, int[] userNumbers) {
+        int ball = 0;
+
+        if (userNumbers[0] == randomNumbers[1] || userNumbers[0] == randomNumbers[2]) {
+            ball += 1;
+        }
+        if (userNumbers[1] == randomNumbers[0] || userNumbers[1] == randomNumbers[2]) {
+            ball += 1;
+        }
+        if (userNumbers[2] == randomNumbers[0] || userNumbers[2] == randomNumbers[1]) {
+            ball += 1;
+        }
+
+        return ball;
+    }
+
+    public static String getStrikeBall(int strike, int ball) {
+        if (strike == 0 && ball == 0) {
+            return "낫싱";
+        } else if (ball == 0) {
+            return strike + "스트라이크";
+        } else if (strike == 0) {
+            return ball + "볼";
+        } else {
+            return ball + "볼 " + strike + "스트라이크";
+        }
+    }
+
+    public static void printEndMessage(int strike) {
+        if (strike == 3) {
+            System.out.println("3개의 숫자를 모두 맞히셨습니다! 게임 종료");
+            System.out.println("게임을 새로 시작하려면 1, 종료하려면 2를 입력하세요.");
+        }
+    }
+
+    public static boolean checkKeepGoing(String userString, int strike) {
+        if (strike != 3) {
+            return true;
+        } else {
+            if (userString.equals("1")) {
+                return true;
+            } else if (userString.equals("2")) {
+                return false;
+            } else {
+                throw new IllegalArgumentException();
+            }
+        }
+    }
+}
diff --git a/src/test/java/UtilityTest.java b/src/test/java/UtilityTest.java
new file mode 100644
index 00000000..d0549b00
--- /dev/null
+++ b/src/test/java/UtilityTest.java
@@ -0,0 +1,124 @@
+import java.util.HashSet;
+import org.junit.jupiter.api.Test;
+import org.assertj.core.api.Assertions;
+
+class UtilityTest {
+
+    @Test
+    void testMakeRandomNumbers() {
+        // 난수를 체크하므로 충분히 많은 테스트를 반복
+        for (int i = 0; i < 1000; i++) {
+            int[] randomNumbers = Utility.makeRandomNumbers();
+
+            Assertions.assertThat(randomNumbers).hasSize(3);
+
+            HashSet<Integer> tempSet = new HashSet<>();
+            for (int randomNumber : randomNumbers) {
+                tempSet.add(randomNumber);
+            }
+            Assertions.assertThat(randomNumbers).hasSize(tempSet.size());
+
+            for (int j = 0; j < 3; j++) {
+                Assertions.assertThat(randomNumbers[j]).isBetween(1, 9);
+            }
+        }
+    }
+
+    @Test
+    void testCheckStringLength() {
+        Assertions.assertThatCode(() -> Utility.checkStringLength("123"))
+            .doesNotThrowAnyException();
+        Assertions.assertThatCode(() -> Utility.checkStringLength("abc"))
+            .doesNotThrowAnyException();
+        Assertions.assertThatCode(() -> Utility.checkStringLength("000"))
+            .doesNotThrowAnyException();
+        Assertions.assertThatThrownBy(() -> Utility.checkStringLength(""))
+            .isInstanceOf(IllegalArgumentException.class);
+        Assertions.assertThatThrownBy(() -> Utility.checkStringLength("11111"))
+            .isInstanceOf(IllegalArgumentException.class);
+        Assertions.assertThatThrownBy(() -> Utility.checkStringLength("zbcda"))
+            .isInstanceOf(IllegalArgumentException.class);
+    }
+
+    @Test
+    void testCheckStringDistinct() {
+        Assertions.assertThatCode(() -> Utility.checkStringDistinct("123"))
+            .doesNotThrowAnyException();
+        Assertions.assertThatCode(() -> Utility.checkStringDistinct("123456789"))
+            .doesNotThrowAnyException();
+        Assertions.assertThatCode(() -> Utility.checkStringDistinct("abc"))
+            .doesNotThrowAnyException();
+        Assertions.assertThatThrownBy(() -> Utility.checkStringDistinct("111"))
+            .isInstanceOf(IllegalArgumentException.class);
+        Assertions.assertThatThrownBy(() -> Utility.checkStringDistinct("12345678910"))
+            .isInstanceOf(IllegalArgumentException.class);
+        Assertions.assertThatThrownBy(() -> Utility.checkStringDistinct("aa"))
+            .isInstanceOf(IllegalArgumentException.class);
+    }
+
+    @Test
+    void testCheckStringDigit() {
+        Assertions.assertThatCode(() -> Utility.checkStringDigit("123")).doesNotThrowAnyException();
+        Assertions.assertThatCode(() -> Utility.checkStringDigit("12345678911112"))
+            .doesNotThrowAnyException();
+        Assertions.assertThatCode(() -> Utility.checkStringDigit("")).doesNotThrowAnyException();
+        Assertions.assertThatThrownBy(() -> Utility.checkStringDigit("1k3"))
+            .isInstanceOf(IllegalArgumentException.class);
+        Assertions.assertThatThrownBy(() -> Utility.checkStringDigit("abc"))
+            .isInstanceOf(IllegalArgumentException.class);
+        Assertions.assertThatThrownBy(() -> Utility.checkStringDigit("1111111110"))
+            .isInstanceOf(IllegalArgumentException.class);
+    }
+
+    @Test
+    void testStringToIntArray() {
+        int[] temp1 = {1, 2, 3};
+        Assertions.assertThat(Utility.stringToIntArray("123")).isEqualTo(temp1);
+        int[] temp2 = {5, 4, 3};
+        Assertions.assertThat(Utility.stringToIntArray("543")).isEqualTo(temp2);
+        int[] temp3 = {2, 4, 6};
+        Assertions.assertThat(Utility.stringToIntArray("246")).isEqualTo(temp3);
+    }
+
+    @Test
+    void testStrikeCount() {
+        int[] randomNumbers = {1, 2, 3};
+        int[] userNumbers = {1, 2, 3};
+        Assertions.assertThat(Utility.strikeCount(randomNumbers, userNumbers)).isEqualTo(3);
+        int[] userNumbers2 = {1, 4, 3};
+        Assertions.assertThat(Utility.strikeCount(randomNumbers, userNumbers2)).isEqualTo(2);
+        int[] userNumbers3 = {1, 4, 5};
+        Assertions.assertThat(Utility.strikeCount(randomNumbers, userNumbers3)).isEqualTo(1);
+        int[] userNumbers4 = {2, 4, 5};
+        Assertions.assertThat(Utility.strikeCount(randomNumbers, userNumbers4)).isEqualTo(0);
+    }
+
+    @Test
+    void testBallCount() {
+        int[] randomNumbers = {1, 2, 3};
+        int[] userNumbers = {2, 3, 1};
+        Assertions.assertThat(Utility.ballCount(randomNumbers, userNumbers)).isEqualTo(3);
+        int[] userNumbers2 = {1, 3, 2};
+        Assertions.assertThat(Utility.ballCount(randomNumbers, userNumbers2)).isEqualTo(2);
+        int[] userNumbers3 = {5, 6, 1};
+        Assertions.assertThat(Utility.ballCount(randomNumbers, userNumbers3)).isEqualTo(1);
+        int[] userNumbers4 = {1, 2, 3};
+        Assertions.assertThat(Utility.ballCount(randomNumbers, userNumbers4)).isEqualTo(0);
+    }
+
+    @Test
+    void testGetStrikeBall() {
+        Assertions.assertThat(Utility.getStrikeBall(3, 0)).isEqualTo("3스트라이크");
+        Assertions.assertThat(Utility.getStrikeBall(1, 1)).isEqualTo("1볼 1스트라이크");
+        Assertions.assertThat(Utility.getStrikeBall(0, 2)).isEqualTo("2볼");
+        Assertions.assertThat(Utility.getStrikeBall(0, 0)).isEqualTo("낫싱");
+    }
+
+    @Test
+    void testCheckKeepGoing() {
+        Assertions.assertThat(Utility.checkKeepGoing("1", 3)).isTrue();
+        Assertions.assertThat(Utility.checkKeepGoing("234", 2)).isTrue();
+        Assertions.assertThat(Utility.checkKeepGoing("2", 3)).isFalse();
+        Assertions.assertThatThrownBy(() -> Utility.checkKeepGoing("3", 3)).isInstanceOf(IllegalArgumentException.class);
+    }
+}
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