springframeworkguru#18 - Degenerate / Immutable Objects "Side Effects"

(cherry picked from commit 7be4ef5)

Author: patrick.corbett@infomotion.de

src/main/java/guru/springframework/Dollar.java

@@ -11,7 +11,7 @@ public Dollar(int pAmount) {
         amount = pAmount;
     }
 
-    void times(int pMultiplier) {
-        amount *= pMultiplier;
+    Dollar times(int pMultiplier) {
+        return new Dollar(amount * pMultiplier);
     }
 }

src/test/java/guru/springframework/MoneyTest.java

@@ -11,8 +11,10 @@ class MoneyTest {
     @Test
     void testMultiplication() {
         Dollar five = new Dollar(5);
-        five.times(2);
-        Assertions.assertEquals(10, five.amount);
+        Dollar product = five.times(2);
+        Assertions.assertEquals(10, product.amount);
+        product = five.times(3);
+        Assertions.assertEquals(15, product.amount);
     }
 
 }