2단계 - 문자열 덧셈 계산기

src/main/java/study/StringAddCalculator/StringAddCalculator.java

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+package study.StringAddCalculator;
+
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+public class StringAddCalculator {
+
+    private static final String COMMENT_PREFIX = "//";
+    private static final Pattern COMMENT_PATTERN = Pattern.compile("//(.)\n(.*)");
+
+    public static int splitAndSum(String text) {
+        if (isEmpty(text)) {
+            return 0;
+        }
+        String[] tokens = extractTokens(text);
+        return add(tokens);
+    }
+
+    // 입력이 null이거나 빈 문자열인지 확인
+    private static boolean isEmpty(String text) {
+        return text == null || text.isEmpty();
+    }
+
+    // 텍스트에서 토큰을 추출 (커스텀 구분자 지원)
+    private static String[] extractTokens(String text) {
+        if (text.startsWith(COMMENT_PREFIX)) {
+            return extractCustomDelimiterTokens(text);
+        }
+        return text.split(",|:");
+    }
+
+    // 커스텀 구분자 형식에서 토큰을 추출
+    private static String[] extractCustomDelimiterTokens(String text) {
+        Matcher m = COMMENT_PATTERN.matcher(text);
+        if (m.find()) {
+            String customDelimiter = m.group(1);
+            return m.group(2).split(Pattern.quote(customDelimiter));
+        }
+        throw new RuntimeException("커스텀 구분자 형식이 올바르지 않습니다.");
+    }
+
+    // 토큰들의 합을 계산
+    private static int add(String[] tokens) {
+        int sum = 0;
+        for (String token : tokens) {
+            sum += parseAndValidateNumber(token);
+        }
+        return sum;
+    }
+
+    // 문자열을 정수로 변환하고 유효성 검사 (음수, 숫자가 아닌 값 체크)
+    private static int parseAndValidateNumber(String token) {
+        int number;
+        try {
+            number = Integer.parseInt(token);
+        } catch (NumberFormatException e) {
+            throw new RuntimeException("숫자가 아닌 값이 포함되어 있습니다: " + token);
+        }
+        if (number < 0) {
+            throw new RuntimeException("음수는 허용되지 않습니다: " + number);
+        }
+        return number;
+    }
+}

src/test/java/study/StringAddCalculator/StringAddCalculatorTest.java

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+package study.StringAddCalculator;
+
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+
+public class StringAddCalculatorTest {
+    @Test
+    public void splitAndSum_null_또는_빈문자() {
+        int result = StringAddCalculator.splitAndSum(null);
+        assertThat(result).isEqualTo(0);
+
+        result = StringAddCalculator.splitAndSum("");
+        assertThat(result).isEqualTo(0);
+    }
+
+    @Test
+    public void splitAndSum_숫자하나() throws Exception {
+        int result = StringAddCalculator.splitAndSum("1");
+        assertThat(result).isEqualTo(1);
+    }
+
+    @Test
+    public void splitAndSum_쉼표구분자() throws Exception {
+        int result = StringAddCalculator.splitAndSum("1,2");
+        assertThat(result).isEqualTo(3);
+    }
+
+    @Test
+    public void splitAndSum_쉼표_또는_콜론_구분자() throws Exception {
+        int result = StringAddCalculator.splitAndSum("1,2:3");
+        assertThat(result).isEqualTo(6);
+    }
+
+    @Test
+    public void splitAndSum_custom_구분자() throws Exception {
+        int result = StringAddCalculator.splitAndSum("//;\n1;2;3");
+        assertThat(result).isEqualTo(6);
+    }
+
+    @Test
+    public void splitAndSum_negative() throws Exception {
+        assertThatThrownBy(() -> StringAddCalculator.splitAndSum("-1,2,3"))
+                .isInstanceOf(RuntimeException.class);
+    }
+}