Question

我是Java编程的新手，并且不知道如何修复当我按下JFrame上的任何一个按钮时发生的错误。我环顾四周，找不到任何东西似乎可以帮助我解决这些问题。这是我的两个按钮的JFrame代码：

    private void btnCheckInActionPerformed(java.awt.event.ActionEvent evt) {                                           
        Patient p = null;

        if (this.rbtnChild.isSelected()) {
            p = new Child();
        }
        else if (this.rbtnAdult.isSelected()) {
            p = new Adult();
        }
        else if (this.rbtnElder.isSelected()) {
            p = new Elder();
        }
        p.name = txtName.getText();
        if(txtName.getText().isEmpty())
        {
            lblValid.setText("Enter a Name.");
        }
        h.CheckIn(p); 
        lblResult.setText(p.name + " successfully checked in.");
        txtName.setText("");
    }                                          

    private void btnProcessActionPerformed(java.awt.event.ActionEvent evt) {                                           
        Doctor d = h.processNext();
        lblResult.setText(d.name + " looked at your patient " + d.currentPatient.name);
        if(q.isEmpty())
        {
            lblProValid.setText("No Patients in Queue.");
        }
    }

当我点击btnProcess时，它会给我这个错误：

Exception in thread "AWT-EventQueue-0" java.util.NoSuchElementException
at java.util.LinkedList.removeFirst(LinkedList.java:268)
at java.util.LinkedList.remove(LinkedList.java:683)
at assignmet.Hospital.processNext(Hospital.java:37)
at assignmet.NewJFrame.btnProcessActionPerformed(NewJFrame.java:231)
at assignmet.NewJFrame.access$400(NewJFrame.java:14)
at assignmet.NewJFrame$5.actionPerformed(NewJFrame.java:94)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2018)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2341)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252)
at java.awt.Component.processMouseEvent(Component.java:6516)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3321)
at java.awt.Component.processEvent(Component.java:6281)
at java.awt.Container.processEvent(Container.java:2229)
at java.awt.Component.dispatchEventImpl(Component.java:4872)
at java.awt.Container.dispatchEventImpl(Container.java:2287)
at java.awt.Component.dispatchEvent(Component.java:4698)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4832)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4492)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4422)
at java.awt.Container.dispatchEventImpl(Container.java:2273)
at java.awt.Window.dispatchEventImpl(Window.java:2719)
at java.awt.Component.dispatchEvent(Component.java:4698)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:740)
at java.awt.EventQueue.access$300(EventQueue.java:103)
at java.awt.EventQueue$3.run(EventQueue.java:699)
at java.awt.EventQueue$3.run(EventQueue.java:697)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:87)
at java.awt.EventQueue$4.run(EventQueue.java:713)
at java.awt.EventQueue$4.run(EventQueue.java:711)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:710)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:242)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:161)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:150)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:146)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:138)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:91)

当我点击btnCheckIn时，它给了我这个错误：

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at assignmet.NewJFrame.btnCheckInActionPerformed(NewJFrame.java:220)
at assignmet.NewJFrame.access$300(NewJFrame.java:14)
at assignmet.NewJFrame$4.actionPerformed(NewJFrame.java:87)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2018)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2341)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252)
at java.awt.Component.processMouseEvent(Component.java:6516)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3321)
at java.awt.Component.processEvent(Component.java:6281)
at java.awt.Container.processEvent(Container.java:2229)
at java.awt.Component.dispatchEventImpl(Component.java:4872)
at java.awt.Container.dispatchEventImpl(Container.java:2287)
at java.awt.Component.dispatchEvent(Component.java:4698)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4832)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4492)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4422)
at java.awt.Container.dispatchEventImpl(Container.java:2273)
at java.awt.Window.dispatchEventImpl(Window.java:2719)
at java.awt.Component.dispatchEvent(Component.java:4698)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:740)
at java.awt.EventQueue.access$300(EventQueue.java:103)
at java.awt.EventQueue$3.run(EventQueue.java:699)
at java.awt.EventQueue$3.run(EventQueue.java:697)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:87)
at java.awt.EventQueue$4.run(EventQueue.java:713)
at java.awt.EventQueue$4.run(EventQueue.java:711)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:710)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:242)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:161)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:150)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:146)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:138)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:91)

这是提到的医院课程：

    package assignmet;


import java.util.ArrayList;
import java.util.LinkedList;
import java.util.Queue;

public class Hospital {

    Queue<Patient> q;
    ArrayList<Doctor> d;

    Hospital() {

        q = new LinkedList<>();
        d = new ArrayList<>();
        d.add(new Doctor("Smith", Qualification.CHILD));
        d.add(new Doctor("Charles", Qualification.ADULT));
        d.add(new Doctor("Jones", Qualification.ELDERLY));

    }

    void CheckIn(Patient p) {
        q.add(p);
    }

    Doctor processNext() {

        Patient p = q.remove();

        for (Doctor doc: d) {

            if (doc.qualification == Qualification.CHILD && 
                    p.getClass() == Child.class)
            {
                doc.currentPatient = p;
                return doc;
            }

            else if (doc.qualification == Qualification.ADULT && 
                    p.getClass() == Adult.class)
            {
                doc.currentPatient = p;
                return doc;
            }

            else if (doc.qualification == Qualification.ELDERLY && 
                    p.getClass() == Elder.class)
            {
                doc.currentPatient = p;
                return doc;
            }

        }

        return null;
    }
}

Answer 1

看起来NoSuchElementException是由在空队列上调用remove方法引起的。确保仅当队列不为空时才启用“处理”按钮。

对于NullPointerException，您可以查看NewJFrame课程的第220行或分享该代码（包含行号），让我们一起来看看。

Answer 2

抛出

NoSuchElementException是因为当队列为空时调用q.remove（）。

抛出

NullPointerException因为p或txtName为空。

Answer 3

由于您使用的是Netbeans，因此使用调试器应该很容易。你在NewJFrame.java：220有一个空指针异常？在那里设置一个断点，看看什么是NULL。如果它是合法地可能为NULL的情况，那么添加一些代码来有条件地执行操作。

如果是不应该为空的情况。然后，您必须深入研究代码，并了解使代码进入错误状态并修复它们的运行时条件。

使用NetBeans的Java：Swing按钮的问题

3 个答案: