Specification is:
-----------------
public IOError(Throwable cause)

    Constructs a new instance of this error, with the specified cause.

    If the cause is not null then the detail string of the new error will be that of the given cause.
-----------------
Questions are:
1) "the detail string" - is it "the detail message" which method getMessage() returns? If yes, it would be nice to formulate it more clear.
2) It is possible to understand such spec by the following way:
       IOError newError = new IOError(cause);
       if (cause != null) then newError.getMessage().equals(cause.getMessage());
 But it is wrong.