HashMap

Question

我从用户那里获取保险详细信息并将其保存在散列图中。                  我有一个名为SAVE的按钮。因此，只有当用户点击此按钮时，所有保险都应保存在数据库中                  所以我将随机生成的id作为参考，直到我将详细信息保存在Database中                  保存在数据库中后，我需要使用key作为自动生成的id

更新此hashmap

public void saveInformationInDatabase(int patientId)
{
    // getAllInsurances returns HashMapn<Integer, HashMap<Integer, InsuranceInformation>>
    Iterator<Map.Entry<Integer, InsuranceInformation>> insurances = getAllInsurances().get(patientId).entrySet().iterator();
    while(insurances.hasNext())
    {
        InsuranceInformation insuranceInformation = insurances.next().getValue();
        if (insuranceInformation.getStatus() == Status.OLD)
            continue;
        else if (insuranceInformation.getStatus() == Status.NEW)
        {
            // Saving the Information in database, and returning auto generated ID
            int licId = saveInformation(insuranceInformation);
            // So, i need to update insuranceInformation with autogenerated ID
            // Because previous id is randomly generated number
            insuranceInformation.setLicID(licId);
            insuranceInformation.setStatus(InsuranceObject.Status.OLD);
            // Below line gives me ConcurrentModificationException
            getAllInsurances().get(patientId).put(licId, insuranceInformation); // Storing the updated information with newly generated id as key, in hashmap
            insurances.remove(); // and here, removing the old hashmap entry
        }
    }
}

Answer 1

getAllInsurances().get(patientId).put(licId, insuranceInformation);正在更新Map，而您正在尝试对其进行迭代，这会导致异常，因为您无法在对其进行迭代时对其进行修改

相反，您应该使用第二个Map来存储更新的值，并使用Map#putAll重新同步这两个值，例如......

// Test map full of values...
Map<Integer, String> mapTest = new HashMap<>(25);
for (int index = 0; index < 10; index++) {
    mapTest.put(index, Integer.toString(index));
}

// Grab an iterator
Iterator<Map.Entry<Integer, String>> insurances = mapTest.entrySet().iterator();
// Create a temp map for the new values
Map<Integer, String> newValues = new HashMap<>(25);
while(insurances.hasNext()) {

    Map.Entry<Integer, String> entry = insurances.next();
    int key = entry.getKey();
    // Make the comparison about what we want to do, here
    // we're removing even keys
    if (key % 2 == 0) {
        // Remove the old entry
        insurances.remove();
        // Use the temp map to create a new entry
        newValues.put(key * 10, entry.getValue());
    }

}

// Merge the results
mapTest.putAll(newValues);

作为一种可能的解决方案