2단계-문자열 덧셈 계산기

src/main/java/study/StringAddCalculator.java

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+package study;
+
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+public class StringAddCalculator {
+    static public int splitAndSum(String text) {
+        if (text == null || text.isEmpty()) {
+            return 0;
+        }
+
+        if (isNumber(text)) {
+            return Integer.parseInt(text);
+        }
+
+        if (text.startsWith("//")) {
+            return getCustomDelimiterSum(text);
+        }
+
+        return getSplitSum(text);
+    }
+
+    static private boolean isNumber(String text) {
+        return text.matches("-?\\d+");
+    }
+
+    static private int getSplitSum(String text) throws RuntimeException {
+        String[] tokens = text.split(",|:");
+        return sumStringToken(tokens);
+    }
+
+    static private int getCustomDelimiterSum(String text) throws RuntimeException {
+        Matcher m = Pattern.compile("//(.)\n(.*)").matcher(text);
+        if (m.find()) {
+            String customDelimiter = m.group(1);
+            String[] tokens= m.group(2).split(customDelimiter);
+            return sumStringToken(tokens);
+        }
+
+        throw new IllegalArgumentException();
+    }
+
+    static private int sumStringToken(String[] tokens) throws RuntimeException {
+        int sum = 0;
+
+        for(String token: tokens) {
+            sum += getSingleNumber(token);
+        }
+        return sum;
+    }
+
+    static private int getSingleNumber(String text) throws RuntimeException {
+        int number = Integer.parseInt(text);
+        if (number < 0) {
+            throw new RuntimeException("음수가 입력되었습니다." + number);
+        }
+        return number;
+    }
+}

src/test/java/study/StringAddCalculatorTest.java

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+package study;
+
+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() {
+        int result = StringAddCalculator.splitAndSum("1");
+        assertThat(result).isEqualTo(1);
+    }
+
+    @Test
+    public void splitAndSum_쉼표구분자() {
+        int result = StringAddCalculator.splitAndSum("1,2");
+        assertThat(result).isEqualTo(3);
+    }
+
+    @Test
+    public void splitAndSum_쉼표_또는_콜론_구분자() {
+        int result = StringAddCalculator.splitAndSum("1,2:3");
+        assertThat(result).isEqualTo(6);
+    }
+
+    @Test
+    public void splitAndSum_custom_구분자() {
+        int result = StringAddCalculator.splitAndSum("//;\n1;2;3");
+        assertThat(result).isEqualTo(6);
+    }
+
+    @Test
+    public void splitAndSum_negative() {
+        assertThatThrownBy(() -> StringAddCalculator.splitAndSum("-1,2,3"))
+                .isInstanceOf(RuntimeException.class);
+    }
+
+    @Test
+    public void splitAndSum_숫자가아닌텍스트() {
+        assertThatThrownBy(() -> StringAddCalculator.splitAndSum("ABC"))
+                .isInstanceOf(IllegalArgumentException.class);
+    }
+}