Abstract: Software watermarking is a software copyright protection technology appeared in recent years．It achieves the purpose of copyright protection by embedding copyright information (watermark) into a software product．This paper proposed a design method of the contradiction structure for the dummy method insertion used in the bytecode based Java software watermark algorithm．The Java reflection mechanism is used to dynamically generate a random string of 0and 1．The string is then encoded and decoded using the technique of the positive and inverse coding to obtain a string of all zeros．This string is used as the condition of the contradiction structure,which ensures that the dummy method will never be executed．The presented contradiction structure has good concealment and can resist various watermark attacks.

Key words: Software watermarking,Dummy method,Permanent false expression,Java reflection mechanism,Positive and inverse code