java - 尝试设置 jcheckbox 时出现 NullPointerException

Question

尝试对其进行设置，以便如果满足特定条件，则将选中两个复选框之一。但是我不断收到 nullpointerexception 错误。

代码是..

        //Set the flat rate or hourly billing check boxes.
    if(flatRateint > 0) {
        InvoiceUI.jCheckBox1.setSelected(true);
    }
    else {
        InvoiceUI.jCheckBox2.setSelected(true);
    }

错误是

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException at my.freelancebillingapp.InvoiceSelectionUI.jButton1MouseClicked(InvoiceSelectionUI.java:224) at my.freelancebillingapp.InvoiceSelectionUI.access$100(InvoiceSelectionUI.java:17) at my.freelancebillingapp.InvoiceSelectionUI$2.mouseClicked(InvoiceSelectionUI.java:86) at java.awt.AWTEventMulticaster.mouseClicked(AWTEventMulticaster.java:253) at java.awt.Component.processMouseEvent(Component.java:6266) at javax.swing.JComponent.processMouseEvent(JComponent.java:3267) at java.awt.Component.processEvent(Component.java:6028) at java.awt.Container.processEvent(Container.java:2041) at java.awt.Component.dispatchEventImpl(Component.java:4630) at java.awt.Container.dispatchEventImpl(Container.java:2099) at java.awt.Component.dispatchEvent(Component.java:4460) at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4574) at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4247) at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4168) at java.awt.Container.dispatchEventImpl(Container.java:2085) at java.awt.Window.dispatchEventImpl(Window.java:2475) at java.awt.Component.dispatchEvent(Component.java:4460) at java.awt.EventQueue.dispatchEvent(EventQueue.java:599) at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:269) at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:184) at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:174) at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:169) at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:161) at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)

Answer 1

假设 InvoiceSelectionUI.java 的第 224 行包含在您的示例中，则以下之一必须为 null:

• 发票UI
• InvoiceUI.jCheckBox1
• InvoiceUI.jCheckBox2
• flatRateint(如果它是 Integer，但如果它是 int，则不是)