refactor: CalculatorApp 객체에서 Input, Print 필드 제거 및 함수화

Author: wonu606

calculator/src/main/java/com/wonu606/calculator/CalculatorApp.java

@@ -18,8 +18,6 @@ public class CalculatorApp implements App {
 
     private final List<Strategy> strategies = new ArrayList<>();
     private final Persistence store = new ResultStore();
-    Input input;
-    Print printer;
 
     public CalculatorApp() {
         initStrategies();
@@ -30,20 +28,29 @@ private void initStrategies() {
     }
 
     public void execute(Input input, Print printer) throws IOException {
-        this.input = input;
-        this.printer = printer;
-
         Converter<String, Integer> stringIntegerConverter = new StringToIntegerConverter();
         while (true) {
-            int selection = stringIntegerConverter.convert(input.getInput());
-
-            Optional<Strategy> selectedStrategy =
-                    Optional.ofNullable(strategies.get(selection - 1));
-            selectedStrategy.ifPresentOrElse(
-                    strategy -> strategy.execute(input, printer, store),
-                    () -> {
-                        throw new IllegalArgumentException("잘못된 입력입니다.");
-                    });
+            int selection = inputMenuSelection(input, stringIntegerConverter);
+            Strategy selectedStrategy = getStrategy(selection);
+            performStrategy(input, printer, selectedStrategy);
+        }
+    }
+
+    private void performStrategy(Input input, Print printer, Strategy selectedStrategy) {
+        selectedStrategy.execute(input, printer, store);
+    }
+
+    private Strategy getStrategy(int selection) {
+        try {
+            return strategies.get(selection - 1);
+        } catch (IndexOutOfBoundsException exception) {
+            throw new IllegalArgumentException(Message.INVALID_INPUT);
         }
     }
+
+    private static int inputMenuSelection(Input input,
+            Converter<String, Integer> stringIntegerConverter)
+            throws IOException {
+        return stringIntegerConverter.convert(input.getInput());
+    }
 }