关于List遍历过程中删除元素报错问题

报错：

java.util.ConcurrentModificationException: null
	at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:909) ~[na:1.8.0_231]
	at java.util.ArrayList$Itr.next(ArrayList.java:859) ~[na:1.8.0_231]

问题代码：

for (RptShiftCashCurrencyNEntity rptShiftCashCurrencyNEntity : rptShiftCashCurrencyNEntityList) {
            if ("B".equals(rptShiftCashCurrencyNEntity.getPosPayType()) || "G".equals(rptShiftCashCurrencyNEntity.getPosPayType()) || "N".equals(rptShiftCashCurrencyNEntity.getPosPayType()) || "8".equals(rptShiftCashCurrencyNEntity.getPosPayType()) || "9".equals(rptShiftCashCurrencyNEntity.getPosPayType())) {
                rptShiftCashCurrencyNEntityList.remove(rptShiftCashCurrencyNEntity);
            }
        }

在解决问题前，先看一段简化代码：

for(String s:list){
    if(s.equals("B")){
        list.remove(x);
    }    
}

这种写法会存在问题，会抛出ConcurrentModificationException。 因为元素在使用的时候发生了并发的修改，导致异常抛出。但是删除完毕马上使用break跳出，则不会触发报错。

解决：

使用迭代器完成删除。

Iterator<String> it = list.iterator();
while(it.hasNext()){
    String s = it.next();
    if(s.equals("B")){
        it.remove();
    }
}

问题代码修改为：

Iterator<RptShiftCashCurrencyNEntity> it = rptShiftCashCurrencyNEntityList.iterator();
        while(it.hasNext()) {
            RptShiftCashCurrencyNEntity rptShiftCashCurrencyNEntity = it.next();
            if ("B".equals(rptShiftCashCurrencyNEntity.getPosPayType()) || "G".equals(rptShiftCashCurrencyNEntity.getPosPayType()) || "N".equals(rptShiftCashCurrencyNEntity.getPosPayType()) || "8".equals(rptShiftCashCurrencyNEntity.getPosPayType()) || "9".equals(rptShiftCashCurrencyNEntity.getPosPayType())) {
                it.remove();
            }
        }

也可以使用java8特性removeIf方法：

rptShiftCashCurrencyNEntityList.removeIf(rptShiftCashCurrencyNEntity -> "B".equals(rptShiftCashCurrencyNEntity.getPosPayType()) || "G".equals(rptShiftCashCurrencyNEntity.getPosPayType()) || "N".equals(rptShiftCashCurrencyNEntity.getPosPayType()) || "8".equals(rptShiftCashCurrencyNEntity.getPosPayType()) || "9".equals(rptShiftCashCurrencyNEntity.getPosPayType()));