java操作Sql出现java.lang.NullPointerException错误
前进的猿 2015-04-24 02:02:52 //我编写了一个java操作sql数据库的类,如下:
package classsource;
import java.sql.*;
public class Database {
public static Connection cn;
public static Statement st;
public static ResultSet rs;
public static boolean joinDB() {
boolean joinFlag;
try {
joinFlag = true;
Class.forName("com.microsoft.sqlserver.jdbc.SQLServerDriver");
cn = DriverManager.getConnection("jdbc:sqlserver://localhost:1433;DatabaseName=EmployeeInformationMS","sa","yourpassword");
cn.setCatalog("EmployeeInformationMS");
System.out.println("数据库连接成功");
st = cn.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE,
ResultSet.CONCUR_READ_ONLY);
return joinFlag;
} catch (SQLException sqlEx) {
System.out.println(sqlEx.getMessage());
joinFlag = false;
return joinFlag;
} catch (ClassNotFoundException notfoundEX) {
System.out.println(notfoundEX.getMessage());
joinFlag = false;
return joinFlag;
}
}
public static boolean executeSQL(String sqlString) {
boolean executeFlag;
try {
st.execute(sqlString);
executeFlag = true;
} catch (Exception e) {
executeFlag = false;
System.out.println("sql exception:" + e.getMessage());
}
return executeFlag;
}
public static boolean query(String sqlString) {
try {
rs = null;
//System.out.println(sqlString);
rs = st.executeQuery(sqlString);
} catch (Exception Ex) {
System.out.println("sql exception:" + Ex);
return false;
}
return true;
}
}
但是运行的时候出现如下错误:sql Exception: java.lang.NullPointerException
求大神指教