The static method java.lang.ThreadLocal.withInitial is added On line 99

src/classes/java/lang/ThreadLocal.java

@@ -21,6 +21,8 @@
 import java.lang.ref.WeakReference;
 import java.util.Objects;
 import java.util.function.Supplier;
+import java.sql.Date;
+import java.text.SimpleDateFormat;
 
 /**
  * model of java.lang.ThreadLocal, which avoids global shared objects
@@ -96,7 +98,10 @@ public void remove(){
   // Java 8 provides this as an internal type to be used from lib classes
   // ?? why is this not done with overridden initialValue() within the concrete ThreadLocal class
   static final class SuppliedThreadLocal<E> extends ThreadLocal<E> {
-
+    public static <S> ThreadLocal<S> withInitial(Supplier<? extends S> supplier) {
+      return new SuppliedThreadLocal<>(supplier);
+    }
+
     // we need to preserve the modifiers since this might introduce races (supplier could be shared)
     private final Supplier<? extends E> sup;
 

src/tests/ThreadLocalTest/App.java

@@ -0,0 +1,21 @@
+import java.sql.Date;
+import java.text.SimpleDateFormat;
+
+class threadSafeFormatter{
+    public static ThreadLocal<SimpleDateFormat> df = ThreadLocal.withInitial(() 
+        -> new SimpleDateFormat("yyyy-MM-dd"));
+}
+
+public class App  {
+    public static void main(String[] args) throws Exception {
+        threadSafeFormatter tf = new threadSafeFormatter();
+        Thread t1 = new Thread();
+        t1.start();
+    }
+
+    public static String birthDate(int userId){
+        Date birthdDate = new Date(userId);
+        final SimpleDateFormat df = threadSafeFormatter.df.get();
+        return df.format(birthdDate);
+    }
+}