无法运行循环哈希图的方法[重复]

Question

private void checkMaxPopularity() throws Exception {
    for (StoredArticle ckeckMax : monitorCombination.keySet()) {
        if (ckeckMax.getTimeAndPopularity().containsValue(5)) {
            monitorCombination.remove(ckeckMax);
            ReadXml newReadXml = new ReadXml();
            StoredArticle replaceArticle = getReplaceArticle();
            monitorCombination.put(replaceArticle, newReadXml);
            // System.out.print("TestTestTesttesttest");
        }
    }
}

请帮助我是 java 新手，我想迭代一个 hashmap 以删除一对键和值。 for 循环中有一个 if 语句来检查哪个值达到 5 然后将其删除。但我得到了这个例外：

java.util.ConcurrentModificationException
at java.util.HashMap$HashIterator.nextEntry(HashMap.java:793)
at java.util.HashMap$KeyIterator.next(HashMap.java:828)
at uk.ac.ncl.fanyaoxia.monitor.MonitorRecentUpdates.checkMaxPopularity(MonitorRecentUpdates.java:138)
at uk.ac.ncl.fanyaoxia.monitor.MonitorRecentUpdates.continueMonitor(MonitorRecentUpdates.java:49)
at uk.ac.ncl.fanyaoxia.gui.MonitorRecentUpdatesGUI.actionPerformed(MonitorRecentUpdatesGUI.java:102)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2028)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2351)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:387)
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:242)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:236)
at java.awt.Component.processMouseEvent(Component.java:6382)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3275)
at java.awt.Component.processEvent(Component.java:6147)
at java.awt.Container.processEvent(Container.java:2083)
at java.awt.Component.dispatchEventImpl(Component.java:4744)
at java.awt.Container.dispatchEventImpl(Container.java:2141)
at java.awt.Component.dispatchEvent(Component.java:4572)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4619)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4280)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4210)
at java.awt.Container.dispatchEventImpl(Container.java:2127)
at java.awt.Window.dispatchEventImpl(Window.java:2489)
at java.awt.Component.dispatchEvent(Component.java:4572)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:710)
at java.awt.EventQueue.access$400(EventQueue.java:82)
at java.awt.EventQueue$2.run(EventQueue.java:669)
at java.awt.EventQueue$2.run(EventQueue.java:667)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:87)
at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:98)
at java.awt.EventQueue$3.run(EventQueue.java:683)
at java.awt.EventQueue$3.run(EventQueue.java:681)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:87)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:680)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:296)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:211)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:201)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:196)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:188)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)

Answer 1

问题是您正在使用来自monitorCombination.keySet() 的迭代器，如果您在迭代时修改地图的内容（添加或删除键），它将引发该异常。试试这个：

private void checkMaxPopularity() throws Exception {
    for (StoredArticle ckeckMax : new HashSet<StoredArticle>(monitorCombination.keySet())) {
        if (ckeckMax.getTimeAndPopularity().containsValue(5)) {
            monitorCombination.remove(ckeckMax);
            ReadXml newReadXml = new ReadXml();
            StoredArticle replaceArticle = getReplaceArticle();
            monitorCombination.put(replaceArticle, newReadXml);
            // System.out.print("TestTestTesttesttest");
        }
    }
}

（我改的部分在for子句里面）