HashMap在遍歷的過程中修改（remove操作）

1.如下的方式刪除鍵值對不會拋出異常

Iterator modifyIter = finalResult.entrySet().iterator();
        while(modifyIter.hasNext()){
            Map.Entry modifyEntry = (Map.Entry)modifyIter.next();
            int keyOut =(int) modifyEntry.getKey();
            HashMap<Integer,ArrayList<Mac>> value = (HashMap<Integer,ArrayList<Mac>>) modifyEntry.getValue();
            Iterator innerIter = value.entrySet().iterator();
            while(innerIter.hasNext()){
                Map.Entry innerEntry = (Map.Entry) innerIter.next();
                int keyIn = (int) innerEntry.getKey();
                ArrayList<Mac> macList = (ArrayList<Mac>) innerEntry.getValue();
                if(macList.size()<groupSize){
                    innerIter.remove();
                    
                }
            }
            if(finalResult.get(keyOut).isEmpty()){
modifyIter.remove(); 18             }
        }

2.否則直接通過finalResult.remove(key)修改hashmap時會在remove()執行之后拋出異常