Implemented strategy pattern tutorial (#1110)

core-java/src/main/java/com/baeldung/strategy/ChristmasDiscounter.java

@@ -0,0 +1,10 @@
+package com.baeldung.strategy;
+
+import java.math.BigDecimal;
+
+public class ChristmasDiscounter implements Discounter {
+    @Override
+    public BigDecimal applyDiscount(final BigDecimal amount) {
+        return amount.multiply(BigDecimal.valueOf(0.9));
+    }
+}

core-java/src/main/java/com/baeldung/strategy/Discounter.java

@@ -0,0 +1,7 @@
+package com.baeldung.strategy;
+
+import java.math.BigDecimal;
+
+public interface Discounter {
+    BigDecimal applyDiscount(BigDecimal amount);
+}

core-java/src/main/java/com/baeldung/strategy/EasterDiscounter.java

@@ -0,0 +1,10 @@
+package com.baeldung.strategy;
+
+import java.math.BigDecimal;
+
+public class EasterDiscounter implements Discounter {
+    @Override
+    public BigDecimal applyDiscount(final BigDecimal amount) {
+        return amount.multiply(BigDecimal.valueOf(0.5));
+    }
+}

core-java/src/test/java/com/baeldung/strategy/StrategyDesignPatternUnitTest.java

@@ -0,0 +1,58 @@
+package com.baeldung.strategy;
+
+import org.junit.Test;
+
+import java.math.BigDecimal;
+import java.util.List;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.util.Lists.newArrayList;
+
+public class StrategyDesignPatternUnitTest {
+    @Test
+    public void shouldDivideByTwo_WhenApplyingStaffDiscounter() {
+        Discounter staffDiscounter = new EasterDiscounter();
+
+        final BigDecimal discountedValue = staffDiscounter
+          .applyDiscount(BigDecimal.valueOf(100));
+
+        assertThat(discountedValue)
+          .isEqualByComparingTo(BigDecimal.valueOf(50));
+    }
+
+    @Test
+    public void shouldDivideByTwo_WhenApplyingStaffDiscounterWithAnonyousTypes() {
+        Discounter staffDiscounter = new Discounter() {
+            @Override
+            public BigDecimal applyDiscount(final BigDecimal amount) {
+                return amount.multiply(BigDecimal.valueOf(0.5));
+            }
+        };
+
+        final BigDecimal discountedValue = staffDiscounter
+          .applyDiscount(BigDecimal.valueOf(100));
+
+        assertThat(discountedValue)
+          .isEqualByComparingTo(BigDecimal.valueOf(50));
+    }
+
+    @Test
+    public void shouldDivideByTwo_WhenApplyingStaffDiscounterWithLamda() {
+        Discounter staffDiscounter = amount -> amount.multiply(BigDecimal.valueOf(0.5));
+
+        final BigDecimal discountedValue = staffDiscounter
+          .applyDiscount(BigDecimal.valueOf(100));
+
+        assertThat(discountedValue)
+          .isEqualByComparingTo(BigDecimal.valueOf(50));
+    }
+
+    @Test
+    public void shouldApplyListOfDiscounts() {
+        List<Discounter> discounters = newArrayList();
+
+        BigDecimal amount = BigDecimal.valueOf(100);
+
+        discounters.forEach((d) -> d.applyDiscount(amount));
+    }
+}