我在使用HashMap时抛出了java.util.ConcurrentModificationException [英] I am getting java.util.ConcurrentModificationException thrown while using HashMap

问题描述

与HashMap中的元素相比，如何删除下面代码中的键值对?

How do i remove the key value pair in the code below comparing with elements in HashMap?

Map<BigDecimal, TransactionLogDTO> transactionLogMap = new HashMap<BigDecimal, TransactionLogDTO>();
for (BigDecimal regionID : regionIdList) {// Generation new logDTO
                                            // objects for each in scope
                                            // region
    transactionLogMap.put(regionID, new TransactionLogDTO());
}
Set<BigDecimal> inScopeActiveRegionIdSet = new HashSet<BigDecimal>();

for (PersonDTO personDTO4 : activePersons) {

    inScopeActiveRegionIdSet.add(personDTO4.getRegion());

}

for (BigDecimal bigDecimal : transactionLogMap.keySet()) {
    if (!inScopeActiveRegionIdSet.contains(bigDecimal)) {
        transactionLogMap.remove(bigDecimal);
    }
}

推荐答案

问题出在这些行中

for (BigDecimal bigDecimal : transactionLogMap.keySet()) {
    if(!inScopeActiveRegionIdSet.contains(bigDecimal)) {
        transactionLogMap.remove(bigDecimal);
    }
}

您正在遍历transactionLogMap，同时还在调用transactionLogMap.remove时直​​接修改了基础Collection，这是不允许的，因为增强的for循环无法看到这些更改.

You are iterating through the transactionLogMap whilst also directly modifying the underlying Collection when you call transactionLogMap.remove, which is not allowed because the enhanced for loop cannot see those changes.

正确的解决方案是使用Iterator:

The correct solution is to use the Iterator:

Iterator<BigDecimal> it = transactionLogMap.keySet().iterator();//changed for syntax correctness
while (it.hasNext()) {
    BigDecimal bigDecimal = it.next();
    if(!inScopeActiveRegionIdSet.contains(bigDecimal)) {
        it.remove();
    }
}

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