diff --git a/build.gradle b/build.gradle
index db8d2fd..5272ea8 100644
--- a/build.gradle
+++ b/build.gradle
@@ -9,6 +9,9 @@ repositories {
 }
 
 dependencies {
+    implementation 'junit:junit:4.12'
+    implementation 'junit:junit:4.12'
+    implementation 'org.testng:testng:7.1.0'
     testCompile('org.junit.jupiter:junit-jupiter:5.6.0')
     testCompile('org.assertj:assertj-core:3.15.0')
 }
diff --git a/settings.gradle b/settings.gradle
new file mode 100644
index 0000000..bcf30bf
--- /dev/null
+++ b/settings.gradle
@@ -0,0 +1,2 @@
+rootProject.name = 'java-calculator'
+
diff --git a/src/README.md b/src/README.md
new file mode 100644
index 0000000..0680f67
--- /dev/null
+++ b/src/README.md
@@ -0,0 +1,61 @@
+# Java-Calculator
+
+Create a string calculator and write test code for it
+
+## Contributor
+- oereo
+
+## Branch structure
+
+### oereo branch
+* from `oereo/java-calculator[oereo branch]` to `biforest/java-calculator [oereo branch]`
+
+### java-calculator-structure branch
+* Feature branch : Branch to develop the function ex)feature/java-calculator
+* Fix branch : Branch to fix the function ex)fix/java-calculator
+
+## TDD
+### Failure case
+#### (1) When divided by 0
+```console
+ 연산을 입력해주세요 : 2/0  // error
+```
+#### (2) When two or more operation symbols appear in a row
+```console
+ 연산을 입력해주세요 : 2++0  // error
+```
+#### (3) When the operation symbol appears at the beginning
+```console
+ 연산을 입력해주세요 : +2+0  // error
+```
+#### (4) When special characters other than operation symbols are entered
+```console
+ 연산을 입력해주세요 : 2^4  // error
+```
+#### (5) When characters excluding numbers and operators are entered
+```console
+ 연산을 입력해주세요 : 2ㄱㄴ4*4  // error
+```
+#### (6) When the formula ends with an operation symbol
+```console
+ 연산을 입력해주세요 : 2-1*  // error
+```
+## Structure
+#### 1. Class
+- Calculator class
+  - `+ class`
+  - `- class`
+  - `* class`
+  - `/ class`
+- Input class
+- Output class
+  - `Error message` output
+  - `Calculation result` output
+- Error exception class
+  - Precautions : only use `try ~ catch`
+- Init class
+  - When an error occurs, reset after outputting an error message
+  - Reset and input when pressing any key value
+    
+#### 2. Algorithm
+- DFS, Node
\ No newline at end of file
diff --git a/src/main/java/calculator/AddOperation.java b/src/main/java/calculator/AddOperation.java
new file mode 100644
index 0000000..29235f1
--- /dev/null
+++ b/src/main/java/calculator/AddOperation.java
@@ -0,0 +1,14 @@
+package calculator;
+
+public class AddOperation implements Operation {
+    @Override
+    public String operationName() {
+        return "+";
+    }
+
+    @Override
+    public int calculation(int beforeNumber, int afterNumber) {
+        int Result = beforeNumber + afterNumber;
+        return Result;
+    }
+}
diff --git a/src/main/java/calculator/Application.java b/src/main/java/calculator/Application.java
new file mode 100644
index 0000000..62e6657
--- /dev/null
+++ b/src/main/java/calculator/Application.java
@@ -0,0 +1,11 @@
+package calculator;
+
+
+public class Application {
+    public static void main(String[] args) {
+
+        // Declare calculator object and start calculation
+        Calculator calculator = new Calculator();
+        calculator.calculation();
+    }
+}
diff --git a/src/main/java/calculator/ArithmeticExpressionStack.java b/src/main/java/calculator/ArithmeticExpressionStack.java
new file mode 100644
index 0000000..1762174
--- /dev/null
+++ b/src/main/java/calculator/ArithmeticExpressionStack.java
@@ -0,0 +1,46 @@
+package calculator;
+
+
+interface Stack{
+    boolean isEmpty();
+    String pop();
+    void clear();
+}
+
+public class ArithmeticExpressionStack implements Stack {
+    private int stackSize;
+    private int flag;
+    private String stack[];
+
+    public ArithmeticExpressionStack(String[] equation, int stackSize){
+        clear();
+        flag = 0;
+        this.stackSize = stackSize;
+        stack = equation;
+    }
+
+    public String pop(){
+        if(isEmpty()){
+            return "스택이 존재하지 않습니다.";
+        }
+        else{
+            return stack[flag++];
+        }
+    }
+
+    public boolean isEmpty(){
+        return (flag == this.stackSize);
+    }
+
+    public void clear(){
+        if(!isEmpty()){
+            flag = -1;
+            this.stackSize = stackSize;
+        }
+    }
+
+    public int getStackSize(){
+        return this.stackSize;
+    }
+
+}
diff --git a/src/main/java/calculator/Calculator.java b/src/main/java/calculator/Calculator.java
new file mode 100644
index 0000000..4099de6
--- /dev/null
+++ b/src/main/java/calculator/Calculator.java
@@ -0,0 +1,143 @@
+package calculator;
+
+import java.util.Scanner;
+
+
+public class Calculator {
+    private Message message = new Message();
+
+    /**
+     * calculation method
+     * 1. getEquation - Receives numeric expression in string format entered by user
+     * 2. Put numeric expressions on the stack
+     * 3. Passing the stack to the operatorSetting method
+     *
+     * return type : void
+     */
+    public void calculation(){
+        String[] equation_list = getEquation();
+        ArithmeticExpressionStack arithmeticExpressionStack = new ArithmeticExpressionStack(equation_list, equation_list.length);
+        OperatorSetting(arithmeticExpressionStack);
+
+    }
+
+    /**
+     * OperatorSetting method
+     * 1. Pop each operator and number onto the stack.
+     * 2. Perform error exception check and calculate
+     * 3. After the calculation process is complete, call init() to determine whether to return the calculator
+     *
+     * return type : void
+     */
+    public void OperatorSetting(ArithmeticExpressionStack arithmeticExpressionStack) {
+        ErrorException exceptionCheck = new ErrorException();
+        String firstString = arithmeticExpressionStack.pop();
+        // Error checking when converting string to int
+        int cumulativeResult = exceptionCheck.NumericalError(firstString);
+
+        for(int i = 0; i<(arithmeticExpressionStack.getStackSize())/2;i++){
+            String operator = arithmeticExpressionStack.pop();
+            String secondString = arithmeticExpressionStack.pop();
+            int secondNumber = exceptionCheck.NumericalError(secondString);
+
+            // calculated value are continuously accumulated
+            cumulativeResult = chooseOperatorAndCalculate(cumulativeResult, operator, secondNumber);
+        }
+
+        if(cumulativeResult != 0){
+            message.calculationResult(cumulativeResult);
+        }
+
+        // Whether to re-execute after calculation
+        init();
+    }
+
+    /**
+     * chooseOperatorAndCalculate method
+     * 1. Pop each operator and number onto the stack.
+     * 2. Perform error exception check and calculate
+     * 3. After the calculation process is complete, call init() to determine whether to return the calculator
+     *
+     * return type : int
+     */
+    public int chooseOperatorAndCalculate(int firstNumber, String operator, int SecondNumber){
+        AddOperation addOperation = new AddOperation();
+        SubOperation subOperation = new SubOperation();
+        MultiplyOperation multiplyOperation = new MultiplyOperation();
+        DivideOperation divideOperation = new DivideOperation();
+        int result = 0;
+
+        // When the operator is equal to "+"
+        if (operator.equals(addOperation.operationName())){
+            result = addOperation.calculation(firstNumber, SecondNumber);
+        }
+
+        // When the operator is equal to "-"
+        else if (operator.equals(subOperation.operationName())){
+            result = subOperation.calculation(firstNumber, SecondNumber);
+        }
+
+        // When the operator is equal to "*"
+        else if (operator.equals(multiplyOperation.operationName())){
+            result = multiplyOperation.calculation(firstNumber, SecondNumber);
+        }
+
+        // When the operator is equal to "/"
+        else if (operator.equals(divideOperation.operationName())){
+            result = divideOperation.calculation(firstNumber, SecondNumber);
+        }
+
+        // Raise error when a symbol that does not correspond to the arithmetic operations(+, -, *, /) comes
+        else{
+            try {
+                throw new Exception();
+            } catch (Exception e) {
+                e.getMessage();
+                message.exceptionResult("NOT_OPERATOR");
+            }
+        }
+
+        return result;
+    }
+
+    /**
+     * init method
+     * - Input "1" to redo calculator.
+     * - Input another key to exit
+     *
+     * return type : void
+     */
+    public void init(){
+        Scanner scanner = new Scanner(System.in);
+        System.out.println("계산을 계속 진행하시려면 1, 멈추시려면 임의의 다른키를 눌러주세요");
+        String value = scanner.nextLine();
+
+        if(value.equals("1")){
+            calculation();
+        }
+        else{
+            System.exit(0);
+        }
+    }
+
+    /**
+     * getEquation method
+     * - Method to receive user input data
+     *
+     * return type : void
+     */
+    String[] getEquation() {
+        String value = inputValues();
+        String[] values = value.split(" ");
+        return values;
+    }
+
+    private String inputValues() {
+        Scanner scanner = new Scanner(System.in);
+        System.out.print("수식을 입력해주세요 : ");
+        String value = scanner.nextLine();
+        return value;
+    }
+
+
+}
diff --git a/src/main/java/calculator/DivideOperation.java b/src/main/java/calculator/DivideOperation.java
new file mode 100644
index 0000000..5333383
--- /dev/null
+++ b/src/main/java/calculator/DivideOperation.java
@@ -0,0 +1,21 @@
+package calculator;
+
+public class DivideOperation implements Operation {
+    @Override
+    public String operationName() {
+        return "/";
+    }
+
+    @Override
+    public int calculation(int beforeNumber, int afterNumber) {
+        Message message = new Message();
+        try{
+            int Result = beforeNumber / afterNumber;
+            return Result;
+        }
+        catch (ArithmeticException e){
+            message.exceptionResult("INVALID_DIVIDE");
+        }
+        return 0;
+    }
+}
diff --git a/src/main/java/calculator/ErrorException.java b/src/main/java/calculator/ErrorException.java
new file mode 100644
index 0000000..dd886e8
--- /dev/null
+++ b/src/main/java/calculator/ErrorException.java
@@ -0,0 +1,23 @@
+package calculator;
+
+public class ErrorException {
+    Message message = new Message();
+
+    /**
+     * NumericalError method
+     * - Raise error when string is not converted to int
+     *
+     * return type : void
+     */
+    public int NumericalError(String number) {
+        int numberConverted = 0;
+        try {
+            numberConverted = Integer.parseInt(number);
+        } catch (NumberFormatException e) {
+            message.exceptionResult("INVALID_EQUATION");
+            Calculator calculator = new Calculator();
+            calculator.init();
+        }
+        return numberConverted;
+    }
+}
diff --git a/src/main/java/calculator/Message.java b/src/main/java/calculator/Message.java
new file mode 100644
index 0000000..fc6db1f
--- /dev/null
+++ b/src/main/java/calculator/Message.java
@@ -0,0 +1,32 @@
+package calculator;
+
+import java.util.HashMap;
+
+/**
+ * Message class
+ * - message output class
+ *
+ * return type : void
+ */
+public class Message {
+    HashMap<String, String> exceptionMessageList = new HashMap<String, String>();
+
+    // Result output method when operation is normally performed
+    public void calculationResult(int result){
+        System.out.print("결과 : ");
+        System.out.println(result);
+    }
+
+    // Error message list management method
+    private void exceptionMessageList(){
+        exceptionMessageList.put("NOT_OPERATOR", "사칙연산 기호에 해당하지 않는 기호가 존재합니다.");
+        exceptionMessageList.put("INVALID_EQUATION", "잘못된 연산식입니다.");
+        exceptionMessageList.put("INVALID_DIVIDE", "0으로 나눌수가 없습니다.");
+    }
+
+    // Error message output method
+    public void exceptionResult(String exceptionKeyword){
+        exceptionMessageList();
+        System.out.println(exceptionMessageList.get(exceptionKeyword));
+    }
+}
diff --git a/src/main/java/calculator/MultiplyOperation.java b/src/main/java/calculator/MultiplyOperation.java
new file mode 100644
index 0000000..420217f
--- /dev/null
+++ b/src/main/java/calculator/MultiplyOperation.java
@@ -0,0 +1,14 @@
+package calculator;
+
+public class MultiplyOperation implements Operation {
+    @Override
+    public String operationName() {
+        return "*";
+    }
+
+    @Override
+    public int calculation(int beforeNumber, int afterNumber) {
+        int Result = beforeNumber * afterNumber;
+        return Result;
+    }
+}
diff --git a/src/main/java/calculator/Operation.java b/src/main/java/calculator/Operation.java
new file mode 100644
index 0000000..77cc374
--- /dev/null
+++ b/src/main/java/calculator/Operation.java
@@ -0,0 +1,12 @@
+package calculator;
+
+interface Operation {
+    String operationName();
+
+    int calculation(int beforeNumber, int afterNumber);
+}
+
+
+
+
+
diff --git a/src/main/java/calculator/SubOperation.java b/src/main/java/calculator/SubOperation.java
new file mode 100644
index 0000000..c1839f9
--- /dev/null
+++ b/src/main/java/calculator/SubOperation.java
@@ -0,0 +1,15 @@
+package calculator;
+
+public class SubOperation implements Operation {
+
+    @Override
+    public String operationName() {
+        return "-";
+    }
+
+    @Override
+    public int calculation(int beforeNumber, int afterNumber) {
+        int Result = beforeNumber - afterNumber;
+        return Result;
+    }
+}
\ No newline at end of file
diff --git a/src/main/java/empty.txt b/src/main/java/empty.txt
deleted file mode 100644
index e69de29..0000000
diff --git a/src/test/java/calculator/CalculatorTest.java b/src/test/java/calculator/CalculatorTest.java
new file mode 100644
index 0000000..67454eb
--- /dev/null
+++ b/src/test/java/calculator/CalculatorTest.java
@@ -0,0 +1,57 @@
+package calculator;
+
+import org.junit.jupiter.api.BeforeEach;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.function.Executable;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+import static org.junit.jupiter.api.Assertions.*;
+
+class CalculatorTest {
+    Calculator calculator;
+    int firstNumber;
+    int secondNumber;
+    String operator;
+
+    @BeforeEach
+    void setUp() {
+        calculator = new Calculator();
+        firstNumber = 2;
+        secondNumber = 3;
+    }
+
+    @Test
+    void addChooseOperatorAndCalculate(){
+        operator = "+";
+        int result = 0;
+        result = calculator.chooseOperatorAndCalculate(firstNumber, operator, secondNumber);
+        assertEquals(5, result);
+        assertThat(5).isEqualTo(result);
+    }
+
+    @Test
+    void subChooseOperatorAndCalculate(){
+        operator = "-";
+        int result = 0;
+        result = calculator.chooseOperatorAndCalculate(firstNumber, operator, secondNumber);
+        assertThat(-1).isEqualTo(result);
+    }
+
+    @Test
+    void multiplyChooseOperatorAndCalculate(){
+        operator = "*";
+        int result = 0;
+        result = calculator.chooseOperatorAndCalculate(firstNumber, operator, secondNumber);
+        assertThat(6).isEqualTo(result);
+    }
+
+    @Test
+    void divideChooseOperatorAndCalculate(){
+        operator = "/";
+        int result = 0;
+        result = calculator.chooseOperatorAndCalculate(firstNumber, operator, secondNumber);
+        assertThat(0).isEqualTo(result);
+    }
+}
\ No newline at end of file