feat: 중위 연산식 유효 검사 클래스 구현

Author: wonu606

calculator/src/main/java/com/wonu606/calculator/validator/InfixValidator.java

@@ -0,0 +1,53 @@
+package com.wonu606.calculator.validator;
+
+import com.wonu606.calculator.model.Operator;
+import java.util.ArrayList;
+import java.util.List;
+
+public class InfixValidator implements Validator {
+
+    private static boolean isExpectedNumericPosition(int position) {
+        return position % 2 == 0;
+    }
+
+    @Override
+    public boolean isValid(String expression) {
+        String[] tokens = expression.split("\\s");
+        List<String> operators = getOperators();
+
+        for (int i = 0; i < tokens.length; i++) {
+            if (isInvalidToken(i, tokens[i], operators)) {
+                return false;
+            }
+        }
+        return true;
+    }
+
+    private boolean isInvalidToken(int position, String str, List<String> operators) {
+        if (isExpectedNumericPosition(position)) {
+            return !isNumeric(str);
+        }
+        return !isOperator(operators, str);
+    }
+
+    private List<String> getOperators() {
+        List<String> operators = new ArrayList<>();
+        for (Operator operator : Operator.values()) {
+            operators.add(operator.symbol);
+        }
+        return operators;
+    }
+
+    private Boolean isNumeric(String str) {
+        try {
+            Double.parseDouble(str);
+        } catch (NumberFormatException e) {
+            return false;
+        }
+        return true;
+    }
+
+    private boolean isOperator(List<String> operators, String expectedOperator) {
+        return operators.contains(expectedOperator);
+    }
+}

calculator/src/main/java/com/wonu606/calculator/validator/Validator.java

@@ -0,0 +1,6 @@
+package com.wonu606.calculator.validator;
+
+public interface Validator {
+
+    boolean isValid(String expression);
+}