Step1 string add calculator

src/main/java/ArithmeticOperator.java

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+import java.util.stream.Stream;
+
+public class ArithmeticOperator {
+    public static int sum(String[] inputs) {
+        return Stream.of(inputs).mapToInt(x-> Integer.parseInt(x)).reduce((a, b)-> a+b).getAsInt();
+    }
+}

src/main/java/Calculator.java

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+public class Calculator {
+
+    public static int getSum(String[] inputs) {
+        if(Validator.checkIfEmpty(inputs) == false){
+            return 0;
+        }
+        return ArithmeticOperator.sum(inputs);
+    }
+}

src/main/java/CalculatorApp.java

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+public class CalculatorApp {
+    public static void main(String[] args) {
+        String input = InputView.getInputs();
+        String[] inputs = Deciferer.extractElements(input);
+        int sum = Calculator.getSum(inputs);
+        OutputView.sumResult(sum);
+    }
+}

src/main/java/Deciferer.java

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+import java.lang.reflect.Array;
+import java.util.Arrays;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+public class Deciferer {
+
+    public static String[] extractElements (String input) {
+        Pattern pattern = Pattern.compile("(//([^\\d])\\\\n)(\\p{Alnum}+)");
+        Matcher matcher = pattern.matcher(input);
+
+        if (matcher.matches()) {
+            String customSeparator = matcher.group(2);
+            String otherString = matcher.group(3);
+            return otherString.split(customSeparator);
+        }
+
+        return input.split(",|;");
+    }
+}

src/main/java/InputView.java

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+import java.util.Scanner;
+
+public class InputView {
+    private static Scanner scanner = new Scanner(System.in);
+
+    public static String getInputs() {
+        return scanner.nextLine();
+    }
+}

src/main/java/OutputView.java

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+public class OutputView {
+    public static void sumResult(int sum) {
+        System.out.println(sum);
+    }
+}

src/main/java/Validator.java

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+public class Validator {
+    public static boolean checkIfEmpty(String[] input) {
+        if(input[0].equals("")){
+            return false;
+        }
+        return true;
+    }
+}

src/test/java/ArithmeticOperatorTest.java

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+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class ArithmeticOperatorTest {
+    private ArithmeticOperator arithmeticOperator;
+    @BeforeEach
+    void setUp() {
+        arithmeticOperator = new ArithmeticOperator();
+    }
+
+    @DisplayName("더하기")
+    @Test
+    public void getSum() {
+        assertThat(arithmeticOperator.sum(new String[] {"1","2","3"})).isEqualTo(6);
+    }
+}

src/test/java/CalculatorTest.java

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+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class CalculatorTest {
+    private Calculator calculator;
+    @BeforeEach
+    void setUp() {
+        calculator = new Calculator();
+    }
+
+    @DisplayName("더하기")
+    @Test
+    public void getSum() {
+        assertThat(calculator.getSum(new String[] {"1","2","3"})).isEqualTo(6);
+        assertThat(calculator.getSum(new String[] {""})).isEqualTo(0);
+    }
+}

src/test/java/DecifererTest.java

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+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class DecifererTest {
+    private Deciferer deciferer;
+    @BeforeEach
+    void setUp() {
+        deciferer = new Deciferer();
+    }
+
+    @DisplayName("문자 추출")
+    @Test
+    public void extractElements() {
+        assertThat(deciferer.extractElements("3;3;3")).isEqualTo(new String[] {"3","3","3"});
+        assertThat(deciferer.extractElements("3,3;3")).isEqualTo(new String[] {"3","3","3"});
+        assertThat(deciferer.extractElements("//a\\n3a3a3")).isEqualTo(new String[] {"3","3","3"});
+        assertThat(deciferer.extractElements("3,3;3")).isEqualTo(new String[] {"3","3","3"});
+    }
+}

src/test/java/ValidatorTest.java

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+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class ValidatorTest {
+    private Validator validator;
+    @BeforeEach
+    void setUp() {
+        validator = new Validator();
+    }
+
+    @DisplayName("더하기")
+    @Test
+    public void getSum() {
+        assertThat(validator.checkIfEmpty(new String[] {"1","2","3"})).isEqualTo(true);
+        assertThat(validator.checkIfEmpty(new String[] {""})).isEqualTo(false);
+    }
+}