Add FactorialCalculatorImpl

src/main/java/ru/ilug/c7_factorial_calculator/FactorialCalculatorImpl.java

@@ -0,0 +1,18 @@
+package ru.ilug.c7_factorial_calculator;
+
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+
+public class FactorialCalculatorImpl implements FactorialCalculator {
+
+    private final Map<Integer, Integer> cache = new ConcurrentHashMap<>();
+
+    @Override
+    public int calculate(int num) {
+        if (num <= 1) {
+            return 1;
+        }
+        return cache.computeIfAbsent(num, n -> calculate(n - 1) * n);
+    }
+
+}

src/main/java/ru/ilug/c7_factorial_calculator/MainTest.java

@@ -6,7 +6,7 @@ import lombok.extern.slf4j.Slf4j;
 public class MainTest {
 
     public static void main(String[] args) {
-        FactorialCalculator factorialCalculator = null;
+        FactorialCalculator factorialCalculator = new FactorialCalculatorImpl();
 
         log.info("Factorial 3 = {}", factorialCalculator.calculate(3));
         log.info("Factorial 4 = {}", factorialCalculator.calculate(4));