问题描述
我想从用户输入插入到名为 accounts 的表中,但这是错误。 它曾经可以工作,但突然间我不知道发生了什么并且不再工作了
线程“main”中的异常java.lang.NullPointerException
在 pl.marcinek.sql.sql.register(sql.java:28)
在 pl.marcinek.accounts.Register.Register(Register.java:32)
在 pl.marcinek.Main.main(Main.java:19)
sql 类
public class sql {
private static Connection conn = null;
private static Staenter code heretement st = null;
private static PreparedStatement preparedStmt = null;
public static void sql() throws ClassNotFoundException,sqlException {
Class.forName("com.MysqL.cj.jdbc.Driver");
conn = DriverManager.getConnection("jdbc:MysqL://localhost:3306/bank","root","");
st = conn.createStatement();
}
public static void register() throws sqlException,ClassNotFoundException {
sql.sql();
String query = " insert into accounts (username,password,name,surname,balance,authcode)" + " values (?,?,?)";
conn.prepareStatement(query);
preparedStmt.setString(1,Register.username); //error
preparedStmt.setString(2,Register.password);
preparedStmt.setString(3,Register.name);
preparedStmt.setString(4,Register.surname);
preparedStmt.setString(5,Register.balance);
preparedStmt.setString(6,Authenticator.authenticator());
preparedStmt.executeUpdate();
}
注册课程
public class Register {
public static String username;
public static String password;
public static String name;
public static String surname;
public static String balance;
public static void Register() throws InterruptedException,sqlException,ClassNotFoundException {
Scanner reg = new Scanner(system.in);
System.out.println("register in this order...");
TimeUnit.SECONDS.sleep(2);
System.out.println("username,balance");
username = reg.nextLine();
password = reg.nextLine();
name = reg.nextLine();
surname = reg.nextLine();
balance = reg.nextLine();
System.out.println("you were correctly registered");
System.out.println("your authenticating code is: ");
sql.register(); //error
TimeUnit.SECONDS.sleep(1);
sql.id();
System.out.println(" ");
System.out.println("dont show your to anyone");
}
}
主类
public class Main {
public static void main(String[] args) throws InterruptedException,ClassNotFoundException {
Scanner scanner = new Scanner(system.in);
System.out.println("choose one");
System.out.println("1:log in");
System.out.println("2:register");
String opcja = scanner.nextLine();
if(opcja.equals("1")){
AccountManager.accoutmanager();
}
if(opcja.equals("2")){
Register.Register(); // Error
}
}
}
解决方法
您忘记将 Connection#prepareStatement()
的调用结果赋值给变量:
conn.prepareStatement(query);
preparedStmt.setString(1,Register.username); //error
应该
preparedStmt = conn.prepareStatement(query);
preparedStmt.setString(1,Register.username);