Looking for standard library or technique to get pretty-printed representation of OBJECT for Java

You could use the ReflectionToStringBuilder from the Apache Commons Lang library.

Sample:

String dump = ReflectionToStringBuilder.toString(object);

As to your question:

m(Object o) can not be called with new Object [] arg?

Sure it can, arrays of Object is a subtype of Object.

For a quick and dirty solution to show the output of a Java object, you could use Jackson http://jackson.codehaus.org/ this will output the object in JSON.