BAEL-1848 final and immutable objects in Java (#4515)

* Strange git issue with README.MD, wouldn't revert the file

* final and immutable objects in Java

* Move tests to src/test/

* BAEL-1848 renamed test class

core-java/src/main/java/com/baeldung/immutableobjects/Currency.java

@@ -0,0 +1,18 @@
+package com.baeldung.immutableobjects;
+
+public final class Currency {
+
+    private final String value;
+    
+    private Currency(String currencyValue) {
+        value = currencyValue;
+    }
+    
+    public String getValue() {
+        return value;
+    }
+    
+    public static Currency of(String value) {
+        return new Currency(value);
+    }
+}

core-java/src/main/java/com/baeldung/immutableobjects/Money.java

@@ -0,0 +1,20 @@
+package com.baeldung.immutableobjects;
+
+// 4. Immutability in Java
+public final class Money {
+    private final double amount;
+    private final Currency currency;
+
+    public Money(double amount, Currency currency) {
+        this.amount = amount;
+        this.currency = currency;
+    }
+
+    public Currency getCurrency() {
+        return currency;
+    }
+
+    public double getAmount() {
+        return amount;
+    }
+}