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
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
String stringSqlString = null;
String tablename = request.getParameter("tablename");
//String tablename = "zbjhb";
if ("flhsk".equals(tablename)) {
stringSqlString = "select gk as 工卡,mc as 名称,bz as 标志,gg as 规格 from flhsk";
} if ("zbjhb".equals(tablename)) {
stringSqlString = "select gk as 工卡,bz as 标志,gg as 规格,dw as 单位 from zbjhb";
}
if ("cpysrb".equals(tablename)) {
stringSqlString = "select gk as 工卡,cpdh as 产品代号,gg as 规格,js as 件数 from cpysrb";
}
if ("scybb".equals(tablename)) {
stringSqlString = "select cpxm as 产品项目,sjgs as 实际工时,swpz as 实完品种,swsl as 实完数量 from scybb";
}
rs = DBbean.executeQuery(stringSqlString);
//显示查询结果
out.print("<Table Border>");
out.print("<TR><td colspan=8 align=center>查询得到的用户数据</td></tr>");
out.print("<TR>");
int i = 1;
for (; i <= 4; i++) {
out.print("<Td width=100 align=center>" + rs.getMetaData().getColumnName(i)+"</TD>");
}
out.print("<Td width=150 >操作</TD>");
while (rs.next()) {
out.print("<TR>");
out.print("<TD >" + rs.getString(1) + "</TD>");
out.print("<TD >" + rs.getString(2) + "</TD>");
out.print("<TD >" + rs.getString(3) + "</TD>");
out.print("<TD >" + rs.getString(4) + "</TD>");
out.print("<Td width=150 >浏览 修改 删除</TD>");
out.print("</TR>");
}
out.print("</Table>");大家再帮忙看一下,SQL语句明明取到了,可为什么出错呢,java.lang.NullPointerException
给stringSqlString赋值就可以,真晕啊,是不是又是低级错误呢?