Step1 string addition calculator

src/main/java/calculator/controller/StringCalculatorApp.java

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+package calculator.controller;
+
+import calculator.model.Calculator;
+import calculator.model.StringReader;
+import calculator.view.Input;
+import calculator.view.Result;
+
+public class StringCalculatorApp {
+    public static void main(String[] args) {
+        Result.showStartMessage();
+        String userInput = Input.getUserInput();
+
+        System.out.println(userInput);
+
+        StringReader stringReader = new StringReader();
+        int[] arr = stringReader.read(userInput);
+
+        Calculator calculator = new Calculator(arr);
+        Result.showResult(calculator.executeAddition());
+    }
+}

src/main/java/calculator/model/Calculator.java

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+package calculator.model;
+
+import java.util.Arrays;
+
+public class Calculator {
+    private final int result;
+
+    public Calculator(int[] numbers) {
+        int minusCount = Arrays.stream(numbers).filter(v -> v < 0).toArray().length;
+        if (minusCount > 0) {
+            throw new RuntimeException();
+        }
+
+        this.result = Arrays.stream(numbers).reduce(Integer::sum).orElse(0);
+    }
+
+    public static Calculator newCalculator(int[] numbers) {
+        return new Calculator(numbers);
+    }
+
+    public int executeAddition() {
+        return this.result;
+    }
+}

src/main/java/calculator/model/StringReader.java

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+package calculator.model;
+
+import java.util.Arrays;
+
+public class StringReader {
+    public int[] read(String str) {
+        String[] arr = str.split("n");
+
+        return arr.length == 1
+                ? withNoCustomSeparator(arr[0])
+                : withCustomSeparator(arr[0], arr[1]);
+    }
+
+    private int[] withNoCustomSeparator(String str) {
+        String[] numbers = str.split("[:,]");
+
+        return Arrays.stream(numbers).mapToInt(Integer::parseInt).toArray();
+    }
+
+    private int[] withCustomSeparator(String separatorPart, String numberPart) {
+        String customSeparator = Character.toString(separatorPart.charAt(2));
+        String regex = "[:," + customSeparator + "]";
+        String[] numbers = numberPart.split(regex);
+
+        return Arrays.stream(numbers).mapToInt(Integer::parseInt).toArray();
+    }
+}

src/main/java/calculator/view/Input.java

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+package calculator.view;
+
+import java.util.Scanner;
+
+public class Input {
+
+    public static String getUserInput() {
+        Scanner scanner = new Scanner(System.in);
+        return scanner.nextLine();
+    }
+}

src/main/java/calculator/view/Result.java

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+package calculator.view;
+
+public class Result {
+
+    public static void showStartMessage() {
+        System.out.println("숫자들을 입력해주세요");
+    }
+
+    public static void showResult(int result) {
+        System.out.printf("합계: %d", result);
+    }
+}

src/test/java/calculator/CalculatorTest.java

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+package calculator;
+
+import calculator.model.Calculator;
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+
+public class CalculatorTest {
+    @Test
+    @DisplayName("with zero parameter")
+    public void nullParameter() {
+        Calculator calculator = Calculator.newCalculator(new int[] { 0 });
+
+        int answer = calculator.executeAddition();
+
+        assertThat(answer).isEqualTo(0);
+    }
+
+    @Test
+    @DisplayName("with only one number parameter")
+    public void oneParameter() {
+        Calculator calculator = Calculator.newCalculator(new int[] { 3 });
+
+        int answer = calculator.executeAddition();
+
+        assertThat(answer).isEqualTo(3);
+    }
+
+    @Test
+    @DisplayName("with array parameter")
+    public void arrayParameter() {
+        Calculator calculator = Calculator.newCalculator(new int[] { 1, 2, 3, 4 });
+
+        int answer = calculator.executeAddition();
+
+        assertThat(answer).isEqualTo(10);
+    }
+
+    @Test
+    @DisplayName("with minus parameter")
+    public void minusParameter() {
+        assertThatThrownBy(() -> Calculator.newCalculator(new int[] { -5 })).isInstanceOf(RuntimeException.class);
+    }
+}

src/test/java/calculator/StringReaderTest.java

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+package calculator;
+
+import calculator.model.StringReader;
+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 StringReaderTest {
+
+    StringReader stringReader;
+
+    @BeforeEach
+    void init() {
+        stringReader = new StringReader();
+    }
+
+    @Test
+    @DisplayName("with multiple numbers parameter")
+    public void multipleNumbers() {
+        assertThat(stringReader.read("1,2,3,4")).isEqualTo(new int[] { 1, 2, 3, 4 });
+    }
+
+    @Test
+    @DisplayName("with only one number parameter")
+    public void onlyOneNumber() {
+        assertThat(stringReader.read("5")).isEqualTo(new int[] { 5 });
+    }
+
+    @Test
+    @DisplayName("with custom separator")
+    public void withSeparator() {
+        assertThat(stringReader.read("//;\\n1:2;3,4")).isEqualTo(new int[] { 1, 2, 3, 4 });
+    }
+}