2단계 - 문자열 덧셈 계산기

src/main/java/calculator/StringAddCalculator.java

@@ -0,0 +1,58 @@
+package calculator;
+
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+public class StringAddCalculator {
+    private static final String DEFAULT_DELIMITER = ",|:";
+    private static final Pattern CUSTOM_DELIMITER = Pattern.compile("//(.)\n(.*)");
+    private static final Pattern INTEGER_PATTERN = Pattern.compile("^-?\\d+$");
+    private static final int DELIMITER_GROUP_INDEX = 1;
+    private static final int INPUT_GROUP_INDEX = 2;
+
+    private StringAddCalculator() {
+        throw new UnsupportedOperationException("유틸 클래스의 인스턴스를 생성할 수 없습니다.");
+    }
+
+    private static boolean isNullOrEmpty(String str) {
+        return str == null || str.isEmpty();
+    }
+
+    private static String[] split(String delimiter, String str) {
+        return str.split(delimiter);
+    }
+
+    private static void validatePositiveIntegerFromString(String str) {
+        if (!INTEGER_PATTERN.matcher(str).matches()) {
+            throw new RuntimeException("숫자만 입력가능하지만 입력받은 문자열은 " + str + "입니다!");
+        }
+        if (Integer.parseInt(str) <= 0) {
+            throw new RuntimeException("양수만 입력가능하지만 입력받은 문자열은 " + str + "입니다!");
+        }
+    }
+
+    private static int sum(String[] numbers){
+        int result = 0;
+        for (String number : numbers) {
+            validatePositiveIntegerFromString(number);
+            result += Integer.parseInt(number);
+        }
+        return result;
+    }
+
+    public static int splitAndSum(String input) {
+        if (isNullOrEmpty(input)) {
+            return 0;
+        }
+
+        String delimiter = DEFAULT_DELIMITER;
+        Matcher customDelimiter = CUSTOM_DELIMITER.matcher(input);
+        if (customDelimiter.find()) {
+            delimiter = customDelimiter.group(DELIMITER_GROUP_INDEX);
+            input = customDelimiter.group(INPUT_GROUP_INDEX);
+        }
+
+        String[] numbers = split(delimiter, input);
+        return sum(numbers);
+    }
+}

src/test/java/calculator/StringAddCalculatorTest.java

@@ -0,0 +1,46 @@
+package calculator;
+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);
+    }
+}