觉得很简单，可为什么总不对，if的问题
String   tablename   =   request.getParameter( "tablename ");
if   (tablename   ==   "flhsk ")   {
        stringSqlString   =   "select   gk   as   工卡,mc   as   名称,bz   as   标志,gg   as   规格   from   flhsk ";
    }
  if   (tablename   ==   "zbjhb ")   {
        stringSqlString   =   "select   gk   as   工卡,bz   as   标志,gg   as   规格,dw   as   单位   from   zbjhb ";
    }
if   (tablename   ==   "cpysrb ")   {
        stringSqlString   =   "select   gk   as   工卡,cpdh   as   产品代号,gg   as   规格,js   as   件数   from   cpysrb ";
    }

高手们，tablename的值可以取到，可为什么stringSqlString的值总为null啊？这个if语句难道有问题？好晕啊◎◎
还有，如果人为tablename   ==   "zbjhb "，stringSqlString的值就不为空了，好奇怪啊

------解决方案--------------------
if ( "flhsk ".equals(tablename))
------解决方案--------------------
java 中判断字符串相等不是 == 而是equals这个方法
------解决方案--------------------
"zbjhb ".equals(tablename)
------解决方案--------------------
java 中判断字符串相等不是 == 而是equals这个方法