A.equals(B)用法 2022-10-08 13:49:48 错误写法:if(User.getUserName.equals(BaseName)) 这样写会报空指针因为:如果User等于空,会报空指针 如果User.getUserName等于空,会报空指针 如果User.getUserName等于空字符串,会报空指针正确写法:if(user!=null&&user.getUserName!=null&&!user.getUserName.equals(" ")&&user.getUserName.equals(BaseName))