code: public BCW getAttribyteBCW(Class c, String name, String methodName, Class returnType)
  	{
  		FieldAccessBCW f = new FieldAccessBCW(c, name, methodName, returnType);
  		return f;
  	}
docs: 获得字节码
  @param c
  @param name
  @param methodName
  @param returnType
  @return