java - 单击按钮时从另一个类调用方法

Question

我已经被这个问题困扰了一段时间了。我一直在网上搜索，但从未找到它的工作方法。每当我单击一个按钮时，我都希望我的程序调用另一个类中的方法；但是，它在我的终端窗口中产生了大量错误，如下所列:

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException at TrackerGUI.actionPerformed(TrackerGUI.java:84) 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:6505) at javax.swing.JComponent.processMouseEvent(JComponent.java:3321) at java.awt.Component.processEvent(Component.java:6270) at java.awt.Container.processEvent(Container.java:2229) at java.awt.Component.dispatchEventImpl(Component.java:4861) at java.awt.Container.dispatchEventImpl(Container.java:2287) at java.awt.Component.dispatchEvent(Component.java:4687) 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:4687) at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:729) at java.awt.EventQueue.access$200(EventQueue.java:103) at java.awt.EventQueue$3.run(EventQueue.java:688) at java.awt.EventQueue$3.run(EventQueue.java:686) 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:702) at java.awt.EventQueue$4.run(EventQueue.java:700) at java.security.AccessController.doPrivileged(Native Method) at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76) at java.awt.EventQueue.dispatchEvent(EventQueue.java:699) 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)

这是我在 GUI 中的代码:

public void actionPerformed(ActionEvent ae)
{
    if (ae.getSource() == button)
    {
        String a = firstField.getText();
        double b = Double.parseDouble(secondField.getText());

        c.call(a, b);
    }
}

firstField 和 secondaryField 是 GUI 中的文本字段。c 是我对另一个类的对象。call(a,b) 是我在另一个类中的方法。

这是我在其他类中的方法:

public boolean call(String a, double b)
{
    if (names.isEmpty() == true)
    {
        names.add(new Name(a, b));
        return true;
    }
    else
    {
        boolean updated = false;

        for (int i = 0; i < names.size(); i++)
        {
            if (names.get(i).getName().contains(f.name))
            {
                names.set(i, new Name(a,b));
                updated = true;
            } 
        }

        if(!updated)
        {
            names.add(new Name(a,b));
        }         
        return true;
    }
}

希望有人能帮帮我!谢谢。

Answer 1

尝试更改此设置:

if (names.isEmpty() == true)
{
    names.add(new Name(a, b));
    return true;
}

对此:

if (names == null)
    names = new ArrayList<>(); //or whatever type names is.

if (names.isEmpty())
{
    names.add(new Name(a, b));
    return true;
}