Question

我正在制作一个程序，允许用户输入名称，然后将其添加并显示在jframe窗口的列表中，但无法弄清楚如何使用代码添加到lsit中。

我尝试了几件事，例如：

lstNames.append(name);
lstNames.Add(name);
lstNames.add(name, this);

（名称是一个字符串）

当前我的代码如下：

DefaultListModel model = new DefaultListModel();
JList list = new JList(model);
ArrayList<String> names;

private void btnAddActionPerformed(java.awt.event.ActionEvent evt) {                                       

    String name = txtFirst.getText() + " " + txtLast.getText(); // works        
    names.add(name); // works

    for (int i = 0; i < names.size(); i++) {
        model.add(i, names.get(i));
    }
    lstNames.setModel(model);

}

我只想在列表中添加一个名称，但是我得到的只是错误，任何帮助都将是很好的。

这是我的错误：

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at javaapplication2.NewJFrame.btnAddActionPerformed(NewJFrame.java:99)
    at javaapplication2.NewJFrame.access$000(NewJFrame.java:12)
    at javaapplication2.NewJFrame$2.actionPerformed(NewJFrame.java:45)
    at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2022)
    at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2348)
    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:6533)
    at javax.swing.JComponent.processMouseEvent(JComponent.java:3324)
    at java.awt.Component.processEvent(Component.java:6298)
    at java.awt.Container.processEvent(Container.java:2236)
    at java.awt.Component.dispatchEventImpl(Component.java:4889)
    at java.awt.Container.dispatchEventImpl(Container.java:2294)
    at java.awt.Component.dispatchEvent(Component.java:4711)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4888)
    at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4525)
    at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4466)
    at java.awt.Container.dispatchEventImpl(Container.java:2280)
    at java.awt.Window.dispatchEventImpl(Window.java:2746)
    at java.awt.Component.dispatchEvent(Component.java:4711)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:758)
    at java.awt.EventQueue.access$500(EventQueue.java:97)
    at java.awt.EventQueue$3.run(EventQueue.java:709)
    at java.awt.EventQueue$3.run(EventQueue.java:703)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76)
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:86)
    at java.awt.EventQueue$4.run(EventQueue.java:731)
    at java.awt.EventQueue$4.run(EventQueue.java:729)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:728)
    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)

直到按下运行代码的按钮，才会出现错误。基本上，我想将用户输入添加到jlist

Answer 1

您没有初始化列表。

ArrayList<String> names;

应该类似于

ArrayList<String> names = new ArrayList<>();

任何方式添加行到JList？

1 个答案: