Question

我建了一个小软件。该软件运行完全正常。在启动软件时，弹出一个选项窗格询问名称，用户可以插入名称然后选择确定或只是取消并终止正在运行的软件。我现在的问题是，如果用户点击取消选项，它会终止然后抛出一堆错误。这些错误我不明白，我已经为我创建的几乎所有方法使用了相应的例外。有没有人对什么有任何建议或想法。

这是RequestAngentName类

public class RequestAgentName{

// instance variable daclaration
private static String uName;

/*
recursive method set username to instance variable
*/

public void setUserName(String name) throws NullPointerException
{       
    name = JOptionPane.showInputDialog(null, "Insert First Name and Last Initial", "Agent Name", 
             JOptionPane.PLAIN_MESSAGE);

    // if user input is not empty
(line 24)if(!name.isEmpty())
    {
        // verify input is acceptable, if yes assign input to global variable
        if(JOptionPane.showConfirmDialog(null, "Is This Your Name?\n\n           " + name, "WARNING" , JOptionPane.YES_NO_OPTION) == JOptionPane.YES_NO_OPTION)
        {
            uName = name;
        } // end if 

        // if input is not acceptable prompt user to reenter name
        else
            // if username is wrong reenter until correct
            this.setUserName(name);


    } // end if

        // if input is empty prompt user to reenter 
        else
            this.setUserName(name);


} //end method set username

// method to return user input 
public String getUserName(){
    return uName;
} // end method get username 

} // end of Request name class

这是我在main中调用它的方式，我觉得可能是错误的地方

RequestAgentName userName = new RequestAgentName();
    try { 
        (line 52) userName.setUserName(userName.getUserName());
        new FNAFrame();
        (new Thread(new FnaComponents())).start(); 
    } 
    catch (NullPointerException npe){
         npe.printStackTrace();
    }

错误如下;

java.lang.NullPointerException
at fna.comments.generator.RequestAgentName.setUserName(RequestAgentName.java:24)
at fna.comments.generator.FNAFrame$1.run(FNAFrame.java:52)
at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:311)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:749)
at java.awt.EventQueue.access$500(EventQueue.java:97)
at java.awt.EventQueue$3.run(EventQueue.java:702)
at java.awt.EventQueue$3.run(EventQueue.java:696)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:75)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:719)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)

建立成功（总时间：6秒）

Answer 1

当你这样做时

name = JOptionPane(...);

当用户按下取消时，JOptionPane返回null。因此，名称为null。

因此

if(!name.isEmpty())

成为

if(!null.isEmpty())

您无法在null上调用方法。因此抛出了NullPointerException。一个简单的解决方案是：

if(name!=null && !name.isEmpty())

修改

我的不好，我没有看到对整个代码的影响。最好像这样解决它：

if (name == null){ // User hit cancel, so simply return/terminate return; } else if (!name.isEmpty()) { // User pressed OK with a value } else // User pressed OK without value

无法弄清楚如何处理这些错误

1 个答案: