The way this is sometimes done in industry, when the copyright owner is known to be litigious, is for developer A to read the code and write a spec. Developer B writes the new implementation based on the spec. If B has any questions, she cannot take to A directly, the questions are routed through a lawyer to make sure that nothing copyrighted is exchanged. (that last part might be overkill, but if the other party is Oracle you might want to use it).

If the developer who does the rewrite uses the original as a reference, it will be likely that enough of the structure will creep through that the project will be at legal risk.