src/java.base/share/classes/java/lang/Class.java

@@ -1,7 +1,7 @@
 /*
- * Copyright (c) 1994, 2018, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1994, 2019, 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
  * under the terms of the GNU General Public License version 2 only, as
  * published by the Free Software Foundation.  Oracle designates this

@@ -3418,12 +3418,12 @@
      */
     private String methodToString(String name, Class<?>[] argTypes) {
         StringBuilder sb = new StringBuilder();
         sb.append(getName() + "." + name + "(");
         if (argTypes != null) {
-            Stream.of(argTypes).map(c -> {return (c == null) ? "null" : c.getName();}).
-                collect(Collectors.joining(","));
+            sb.append(Stream.of(argTypes).map(c -> {return (c == null) ? "null" : c.getName();}).
+                      collect(Collectors.joining(",")));
         }
         sb.append(")");
         return sb.toString();
     }