现有异常类型，不能表示业务中的错误情况，可以自定义新的异常类型
1起一个合适的类名
UserNameNotFoundException
WrongPasswordException
2选择一个合适父类
Exception(没有管道，需要throws管道)
RuntimeException(有默认管道)
添加合适的构造方法
例子：
用户登录，用户名错误或密码错误，分别用两个异常类型来表示

UserNameNotFoundException
WrongPasswordException

public class UserNameNotFoundException extends Exception{

    private static final long serialVersionUID = 1L;

    public UserNameNotFoundException() {
        super();
    }

    public UserNameNotFoundException(String message, Throwable cause, boolean enableSuppression,
            boolean writableStackTrace) {
        super(message, cause, enableSuppression, writableStackTrace);
    }

    public UserNameNotFoundException(String message, Throwable cause) {
        super(message, cause);
    }

    public UserNameNotFoundException(String message) {
        super(message);
    }

    public UserNameNotFoundException(Throwable cause) {
        super(cause);
    }
    

}

public class WrongPasswordException extends Exception{

    private static final long serialVersionUID = 1L;

    public WrongPasswordException() {
        super();
    }

    public WrongPasswordException(String message, Throwable cause, boolean enableSuppression,
            boolean writableStackTrace) {
        super(message, cause, enableSuppression, writableStackTrace);
    }

    public WrongPasswordException(String message, Throwable cause) {
        super(message, cause);
    }

    public WrongPasswordException(String message) {
        super(message);
    }

    public WrongPasswordException(Throwable cause) {
        super(cause);
    }
    
    

}

public class UserDefineException {
    public static void main(String[] args) {
        String userName = "apple";
        String password = "123";
        handleLogin(userName, password);
        userName = "admin";
        password = "456";
        handleLogin(userName, password);
        password = "123";
        handleLogin(userName, password);
    }

    public static void handleLogin(String userName, String password) {
        try {
            login(userName, password);
            System.out.println("登录成功");
        } catch (UserNameNotFoundException e) {
            System.out.println("用户名错误");
        } catch (WrongPasswordException e) {
            System.out.println("密码错误");
        }
    }

    private static void login(String userName, String password)
            throws UserNameNotFoundException, WrongPasswordException {
        if (!userName.equals("admin"))
            throw new UserNameNotFoundException();
        if (!password.equals("123"))
            throw new WrongPasswordException();

    }
}

运行结果

用户名错误
密码错误
登录成功