说明：  本文首先分析了Java源代码需要加密的原因，简要介绍了DES算法及Java密码体系和Java密码扩展，最后说明了利用DES加密算法保护Java源代码的方法及步骤
(This paper analyzes the Java source code encryption needs, briefed the DES algorithm and system password Java and Java code expansion Finally, we illustrate the use of DES encryption algorithm to protect the source code of Java methods and steps)