Question

我不知道为什么它与使用该参数的帐户进行比较时总是返回false。如果帐户是硬编码的，它只会返回true。

public class Account
{
    public Account(String username, String password, String lastname, String firstname){
        this.username = username;
        this.password = password;
        this.firstname = firstname;
        this.lastname = lastname;
    }

    public String getUsername() {
        return username;
    }

    public String getPassword() {
        return password;
    }

    public String getFirstname() {
        return firstname;
    }

    public String getLastname() {
        return lastname;
    }


    private String username;
    private String password;
    private String firstname;
    private String lastname;
    public boolean equals(Object obj)
    {
        boolean result = false;
        if (obj != null && obj instanceof Account)
        {
            Account p = (Account)obj;
            if ( getUsername().equals(p.getUsername()) 
              && getPassword() == p.getPassword() )
            {
                result = true;
            }
        }
        return result;
    }
}

我的Servlet

Set<Account> acc = new HashSet<Account>();

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doPost(request, response);
    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setContentType("text/html");
        acc.add(new Account("test1", "pass123", "Boom", "Bang"));
            acc.add(new Account("test2", "pass123", "Beam", "Beng"));
        PrintWriter out = response.getWriter();
        String username = "";
        String password = "";


    if(request.getParameter("Username") != null){
        username = request.getParameter("Username");
    }
    if(request.getParameter("Password") != null){
        password = request.getParameter("Password");
    }

    Account act1 = new Account(username, password, "", "","");
            System.out.print(username+password); // test if the username and password change based on the parameter
            /*
            Works only on hard code
            Account act1 = new Account("test1", "pass123", "", "","");
            */

        out.print("<html>");
        out.print("<head><link href='layoutit/css/bootstrap.min.css' rel='stylesheet'>"
                + "<link href='layoutit/css/style.css' rel='stylesheet'>");
        out.print("<title></title>");
        out.print("</head>");
        out.print("<body");
        if(acc.contains(act1)){ // the condition that always return false if not hardcode
                out.print("<h3>Click <a href='displayuser.html'>here</a> to continue.</h3>");
        }
    else
        out.print("<h1>Invalid user account entered.Click <a href='index.html'>here</a> to login.</h1>");
        out.print("</body>");
        out.print("</hmtl>");
        out.close();
    }

Answer 1

比较密码时，请使用.equals代替==。

（从我对该问题的评论中复制）

Answer 2

密码也是字符串，但您使用==进行比较，使用.equals。从下面使用如下：

      if ( getUsername().equals(p.getUsername()) 
          && getPassword() == p.getPassword() )

要

   if ( getUsername().equals(p.getUsername()) 
          && getPassword().equals(p.getPassword()) )

此外，当您使用instanceof运算符时，不需要单独的空值检查。

所以，你可以写这一行

if (obj != null && obj instanceof Account)

as

if (obj instanceof Account)

在比较使用参数的对象时始终返回false

2 个答案: