Refactor Discounter examples

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

@@ -3,8 +3,9 @@ package com.baeldung.strategy;
 import java.math.BigDecimal;
 
 public class ChristmasDiscounter implements Discounter {
+
     @Override
-    public BigDecimal applyDiscount(final BigDecimal amount) {
+    public BigDecimal apply(BigDecimal amount) {
         return amount.multiply(BigDecimal.valueOf(0.9));
     }
 }

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

@@ -1,7 +1,19 @@
 package com.baeldung.strategy;
 
 import java.math.BigDecimal;
+import java.util.function.UnaryOperator;
 
-public interface Discounter {
-    BigDecimal applyDiscount(BigDecimal amount);
+public interface Discounter extends UnaryOperator<BigDecimal> {
+
+    static Discounter christmas() {
+        return (amount) -> amount.multiply(BigDecimal.valueOf(0.9));
+    }
+
+    static Discounter newYear() {
+        return (amount) -> amount.multiply(BigDecimal.valueOf(0.8));
+    }
+
+    static Discounter easter() {
+        return (amount) -> amount.multiply(BigDecimal.valueOf(0.5));
+    }
 }

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

@@ -3,8 +3,9 @@ package com.baeldung.strategy;
 import java.math.BigDecimal;
 
 public class EasterDiscounter implements Discounter {
+
     @Override
-    public BigDecimal applyDiscount(final BigDecimal amount) {
+    public BigDecimal apply(BigDecimal amount) {
         return amount.multiply(BigDecimal.valueOf(0.5));
     }
 }