feat: 연산자 구현

Author: wonu606

calculator/src/main/java/com/wonu606/calculator/model/Operator.java

@@ -0,0 +1,52 @@
+package com.wonu606.calculator.model;
+
+import com.wonu606.calculator.util.CalculatorMessage;
+
+public enum Operator {
+    ADD("+", 2){
+        @Override
+        public double apply(double a, double b) {
+            return a + b;
+        }
+    },
+    SUBTRACT("-", 2) {
+        @Override
+        public double apply(double a, double b) {
+            return a - b;
+        }
+    },
+    MULTIPLY("*", 1) {
+        @Override
+        public double apply(double a, double b) {
+            return a * b;
+        }
+    },
+    DIVIDE("/", 1) {
+        @Override
+        public double apply(double a, double b) {
+            if (b == 0) {
+                throw new ArithmeticException(CalculatorMessage.NOT_DIVISIBLE_BY_ZERO.message);
+            }
+            return a / b;
+        }
+    };
+
+    public final String symbol;
+    public final int precedence;
+
+    Operator(String symbol, int precedence) {
+        this.symbol = symbol;
+        this.precedence = precedence;
+    }
+
+    public abstract double apply(double a, double b);
+
+    public static Operator get(String symbol) {
+        for (Operator operator : values()) {
+            if (operator.symbol.equals(symbol)) {
+                return operator;
+            }
+        }
+        return null;
+    }
+}

calculator/src/main/java/com/wonu606/calculator/util/CalculatorMessage.java

@@ -2,7 +2,8 @@
 
 public enum CalculatorMessage {
     INVALID_ORDER("잘못된 순번입니다."),
-    INVALID_INPUT("잘못된 입력입니다.");
+    INVALID_INPUT("잘못된 입력입니다."),
+    NOT_DIVISIBLE_BY_ZERO("0으로 나눌 수 없습니다.");
 
     public final String message;