Step2 : 문자열 덧셈 계산기

src/main/java/step2/ParsedInput.java

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+package step2;
+
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+public class ParsedInput {
+    private static final String DEFAULT_DELIMITER = ",|:";
+    private String delimiter = DEFAULT_DELIMITER;
+    private String[] numbers;
+
+    public ParsedInput(String input) {
+        parseInput(input);
+    }
+
+    public String[] getNumbers() {
+        return numbers;
+    }
+
+    private void parseInput(String input) {
+        Pattern pattern = Pattern.compile("//(.)\\n(.*)");
+        Matcher matcher = pattern.matcher(input);
+
+        if (matcher.find()) {
+            delimiter = matcher.group(1);
+            input = matcher.group(2);
+        }
+
+        numbers = input.split(delimiter);
+    }
+}

src/main/java/step2/StringAddCalculator.java

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+package step2;
+
+public class StringAddCalculator {
+    public static int splitAndSum(final String input) {
+        if (input == null || input.isBlank()) {
+            return 0;
+        }
+
+        return sumParsedNumbers(new ParsedInput(input).getNumbers());
+    }
+
+    private static int sumParsedNumbers(String[] numbers) {
+        int total = 0;
+
+        for (String number : numbers) {
+            int parsed = Integer.parseInt(number);
+            if (parsed < 0) {
+                throw new RuntimeException("음수는 입력 불가 합니다.");
+            }
+
+            total += parsed;
+        }
+
+        return total;
+    }
+
+}

src/test/java/step2/StringAddCalculatorTest.java

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+package step2;
+
+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);
+    }
+}