diff --git a/src/main/java/Calculator.java b/src/main/java/Calculator.java
new file mode 100644
index 00000000..407e341a
--- /dev/null
+++ b/src/main/java/Calculator.java
@@ -0,0 +1,50 @@
+public class Calculator {
+    int add(int a, int b) {
+        return a + b;
+    }
+
+    int subtract(int a, int b){
+        return a - b;
+    }
+    int multiply(int a, int b){
+        return a * b;
+    }
+    int divide(int a, int b){
+        return a / b;
+    }
+
+    public int calculateString(String input) {
+        if (input == null | input.isEmpty()) {
+            return 0;
+        }
+
+        String separator = "[,:]";//정규표현식. split()메소드에서 사용된다. '[]안의 문자중 하나와 일치'라는 의미를 갖는다.
+        String numbersStr = input;
+
+        if (input.substring(0, 2).equals("//")) {
+            int slashStartIndex = input.indexOf("//");
+            int newLineStartIndex = input.indexOf("/n");
+
+            if (newLineStartIndex != -1) {
+                String customSeparator = input.substring(slashStartIndex + 2, newLineStartIndex);
+                separator = "[,:" + customSeparator + "]";
+                numbersStr = input.substring(newLineStartIndex + 1);//개행문자는 하나의 문자로 취급.
+            }
+        }
+
+            String[] numbers = numbersStr.split(separator);
+
+            int sum = 0;
+            for (String number : numbers) {
+                if (!number.isEmpty()) {
+                    int value = Integer.parseInt(number);//String 배열에 있는 numbers를 하나씩 int형으로 변환
+                    if (value < 0) {
+                        throw new RuntimeException("음수는 사용할 수 없습니다 : " + value);
+                    }
+                    sum += value;
+                }
+            }
+            return sum;
+    }
+}
+
diff --git a/src/test/java/CalculatorTest.java b/src/test/java/CalculatorTest.java
new file mode 100644
index 00000000..51937dde
--- /dev/null
+++ b/src/test/java/CalculatorTest.java
@@ -0,0 +1,41 @@
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public class CalculatorTest {
+    Calculator c = new Calculator();
+
+    @Test
+    void testAdd(){
+        int result = c.add(2,3);
+        assertEquals(5,result);
+    }
+    @Test
+    void testSubtract(){
+        int result = c.subtract(2,3);
+        assertEquals(-1,result);
+    }
+
+    @Test
+    void testMultiply(){
+        int result = c.multiply(2,3);
+        assertEquals(6,result);
+    }
+    @Test
+    void testDivide(){
+        int result = c.divide(6,3);
+        assertEquals(2,result);
+    }
+
+    @Test
+    void testCalculateString(){
+        int result = c.calculateString("1,2:3");
+        assertEquals(6,result);
+        result = c.calculateString("");
+        assertEquals(0,result);
+        result = c.calculateString("1,2");
+        assertEquals(3,result);
+        result = c.calculateString("1,2,3");
+        assertEquals(6,result);
+    }
+}