JDK 16 RFR of 8250580: Address reliance on default constructors in java.rmi

[Joe Darcy]

Hello,

Another bug in the quest to remove use of default constructors in the 
JDK's public API, this time in the java.rmi module:

     webrev: http://cr.openjdk.java.nhet/~darcy/8250580.0/
     CSR: https://bugs.openjdk.java.net/browse/JDK-8250581

Patch below; thanks,

-Joe

--- 
old/src/java.rmi/share/classes/java/rmi/server/RMIClassLoaderSpi.java 
2020-07-24 19:42:16.353847343 -0700
+++ 
new/src/java.rmi/share/classes/java/rmi/server/RMIClassLoaderSpi.java 
2020-07-24 19:42:15.645847343 -0700
@@ -1,5 +1,5 @@
  /*
- * Copyright (c) 2000, 2006, Oracle and/or its affiliates. All rights 
reserved.
+ * Copyright (c) 2000, 2020, Oracle and/or its affiliates. All rights 
reserved.
   * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   *
   * This code is free software; you can redistribute it and/or modify it
@@ -62,6 +62,11 @@
  public abstract class RMIClassLoaderSpi {

      /**
+     * Constructor for subclasses to call.
+     */
+    public RMIClassLoaderSpi() {}
+
+    /**
       * Provides the implementation for
       * {@link RMIClassLoader#loadClass(URL,String)},
       * {@link RMIClassLoader#loadClass(String,String)}, and