JPasswordField KeyPress字符串长度错误? [英] JPasswordField KeyPress string length error?

问题描述

我正在尝试更改Java Swing(Netbeans)中JPasswordField的背景颜色.

这就是我所拥有的:

private void pstxtPasswordKeyPressed(java.awt.event.KeyEvent evt) {                                         

    //Get string from password box
    userPassword = new String(pstxtPassword.getPassword());

    //If password is 8+ characters
    //(one less because string counting begins at 0)
    if (userPassword.length() >= 7) {

        //Set password input box background color to green
        pstxtPassword.setBackground(Color.green);
    }

    else { //If password is less than 8 characters

        //Set password input box background color to red
        pstxtPassword.setBackground(Color.red);
    }

}

一切正常，除非我退格.当我输入8个以上的字符后退格时，颜色不会变回红色，直到字段中只剩下5个字符为止.

我们将非常感谢您的帮助，我对Java编程和Netbeans还是陌生的.

我已经更改了代码，

    //If password is 8+ characters
    if ((pstxtPassword.getPassword()).length >= 8) {

        //Set password input box background color to green
        pstxtPassword.setBackground(Color.green);
    }

    else { //If password is less than 8 characters

        //Set password input box background color to red
        pstxtPassword.setBackground(Color.red);
    }

这段代码对我来说似乎很有意义，但是在测试中，第9个字符的颜色变为绿色；当退格时，它在6时变回红色.这似乎是我在代码为>= 7时遇到的相同问题，其中代码的第8个字符变为绿色，而第5个字符变为红色.

输入9个字符后，组件变为绿色

退格(从9开始)后，组件将保持绿色，直到有6个字符为止

这很奇怪，因为我在该程序的一个按钮中有类似的代码，该代码显示错误消息.该代码工作正常. 这是KeyPress问题吗，也许与退格键有关?

顺便说一句，检查getPassword()返回的数组的长度，而不是从该数组构造的String的长​​度. String有安全隐患，因为它会以容易找到的名称userPassword无限期存储.

附录:这是罗宾(Robin)的 解决方案

As an aside, examine the length of the array returned by getPassword(), rather than the length of a String constructed from that array. The String is a security risk, as it will be stored for an indefinite time with the easily found name userPassword.

Addendum: Here's a related example of Robin's suggestion to use DocumentListener. I'm guessing that your key listener is seeing the KeyEvent before the JPasswordField has processed it.

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