DOcument thread-safety of "mutable" static fields (actually write-once)

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/math/trunk@1296529 13f79535-47bb-0310-9956-ffa450edef68

src/main/java/org/apache/commons/math3/dfp/DfpField.java

@@ -75,6 +75,8 @@ public class DfpField implements Field<Dfp> {
     /** High precision string representation of &radic;2. */
     private static String sqr2String;
 
+    // Note: the static strings are set up (once) by the ctor and @GuardedBy("DfpField.class")
+
     /** High precision string representation of &radic;2 / 2. */
     private static String sqr2ReciprocalString;