Question

我遇到了问题，我无法理解为什么会这样。

我想在JLayeredPane上添加一些带有一些按钮的JLayeredPane。单击此按钮之一时，我想删除第一个JLayeredPane，即第二个JLayeredPane。

这是我尝试删除第二个JLayeredPane

的方法

public void clearAsk() throws ClassCastException {
    Component[] components = layeredPane.getComponentsInLayer(2);
    for(int i=0;i<components.length;i++){
        JLayeredPane toClear = (JLayeredPane) components[i];
        toClear.removeAll();
        toClear.validate();
        layeredPane.remove(components[i]);
        layeredPane.validate();
    }
    layeredPane.validate();
    layeredPane.repaint();
}

调用此方法时，有时会（不总是）显示以下异常。

Exception in thread "AWT-EventQueue-0" java.lang.ClassCastException
at javax.swing.LayoutComparator.compare(Unknown Source)
at javax.swing.LayoutComparator.compare(Unknown Source)
at java.util.TimSort.binarySort(Unknown Source)
at java.util.TimSort.sort(Unknown Source)
at java.util.Arrays.sort(Unknown Source)
at java.util.Collections.sort(Unknown Source)
at javax.swing.SortingFocusTraversalPolicy.enumerateAndSortCycle(Unknown Source)
at javax.swing.SortingFocusTraversalPolicy.getFocusTraversalCycle(Unknown Source)
at javax.swing.SortingFocusTraversalPolicy.getComponentAfter(Unknown Source)
at javax.swing.LayoutFocusTraversalPolicy.getComponentAfter(Unknown Source)
at java.awt.Component.getNextFocusCandidate(Unknown Source)
at java.awt.DefaultKeyboardFocusManager.doRestoreFocus(Unknown Source)
at java.awt.DefaultKeyboardFocusManager.restoreFocus(Unknown Source)
at java.awt.DefaultKeyboardFocusManager.dispatchEvent(Unknown Source)
at java.awt.Component.dispatchEventImpl(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
at java.awt.EventQueue.access$400(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.run(Unknown Source)

为什么会这样？为什么它并不总是发生？我真的无法找到解决这个问题的方法......

Answer 1

当您浏览图层中的所有组件时，您可能会认为每个组件都是JLayeredPane，而实际上它实际上是其他组件。相反，您可以做的是在删除组件之前安全地检查该组件是否是 instanceof JLayeredPane：

public void clearAsk() throws ClassCastException {
    Component[] components = layeredPane.getComponentsInLayer(2);
    for(int i=0;i<components.length;i++){
        if(components[i] instanceof JLayeredPane) { 
            JLayeredPane toClear = (JLayeredPane) components[i];
            toClear.removeAll();
            toClear.validate();
            layeredPane.remove(components[i]);
            layeredPane.validate();
        }
    }
    layeredPane.validate();
    layeredPane.repaint();
}

从JLayeredPane中删除组件时的java.lang.ClassCastException

1 个答案: