Add example of lightweight strategy

Author: mperor

DesignPatterns/src/test/java/pl/mperor/lab/java/design/pattern/behavioral/strategy/LightweightStrategyTest.java

@@ -0,0 +1,37 @@
+package pl.mperor.lab.java.design.pattern.behavioral.strategy;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+import java.util.List;
+import java.util.function.Predicate;
+
+public class LightweightStrategyTest {
+
+    @Test
+    public void testTotalValueStrategy() {
+        var values = List.of(1, 2, 3, 4);
+        Assertions.assertEquals(10, totalValue(values));
+        Assertions.assertEquals(6, totalValue(values, LightweightStrategyTest::isEven));
+        Assertions.assertEquals(4, totalValue(values, LightweightStrategyTest::isOdd));
+    }
+
+    public static int totalValue(List<Integer> values) {
+        return totalValue(values, _ -> true);
+    }
+
+    public static int totalValue(List<Integer> values, Predicate<Integer> selector) {
+        return values.stream()
+                .filter(selector)
+                .mapToInt(e -> e)
+                .sum();
+    }
+
+    public static boolean isEven(int number) {
+        return number % 2 == 0;
+    }
+
+    public static boolean isOdd(int number) {
+        return !isEven(number);
+    }
+}