java.util.ConcurrentModificationException: null

问题

1.实例

Exception in thread "main" java.util.ConcurrentModificationException
	at java.util.HashMap.forEach(HashMap.java:1292)
	at com.geo.source.testmain.publictest.MapTest.m5(MapTest.java:21)
	at com.geo.source.testmain.publictest.MapTest.main(MapTest.java:15)

 2.开发时遇到的问题

解决方案

    private static void m4() {
        final HashMap<Long, Long> map = new HashMap<>(1);
        map.put(1L, 1L);
        final Set<Long> ids = new HashSet<>(map.keySet());
        for (Long id : ids) {
            map.remove(id);
        }

        System.out.println(map);
    }

 原因

动动手，翻翻源码！