Question

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);
    }
}

Answer 1

The problem is in these lines

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

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.

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();
    }
}