java - 将值添加到 HashMap 中的列表对象

Question

我正在尝试将列表对象添加到 HashMap

我尝试了以下代码，但没有成功

public static Map<Long, List<Long>>  getCellAttributes(List<Vo> voList){

    LOG.info("VO: {}", Arrays.toString(VO.toArray()));

    Map<Long, List<Long>> atributesMap = new HashMap();

    List<Long> cellList = new ArrayList<>();

    for(: VOList){
        Long cID = VO.getID();
        Long cellUserNumber = VO.getCellNumber();
        if(cellMap.containsKey(ID)){
            cellList.add(cellNumber);
            cellmap.put(ID, list);
        }
        else {
            Map.put(ID, cellAtributesMap.get(ID).add(cellNumber));
        }
    }
    return cellMao;
}

发现 else block 部分出现以下错误。

Wrong 2nd argument type. Found: 'boolean', required:

Answer 1

好的，首先，else block 中的 Map.put 是什么？对我来说，这在逻辑上听起来是错误的，可能您的意思是 campaignId 尚未出现在 map 中的情况。在这种情况下，您可以:

else {
   List<Long> cellList = new ArrayList<>();
   cellList.add(cellUserNumber);
   cellAtributesMap.put(campaignId, cellList);
} 

现在 if block 在逻辑上看起来也是错误的，不需要维护全局列表(如果 targetedOffersCampaignVOList 没有排序怎么办)并且不需要每次都放入到 map 中。

因为这对我来说似乎不是作业，所以这里有一个更好的版本:

Map<Long, List<Long>> cellAtributesMap = new HashMap();

// note, the following line is not required and should be removed
//List<Long> cellList = new ArrayList<>();

for(TargetedOffersCampaignVO targetedOffersCampaignVO: targetedOffersCampaignVOList){
    Long campaignId = targetedOffersCampaignVO.getCampaignID();
    Long cellUserNumber = targetedOffersCampaignVO.getCellUserNumber();
    if(cellAtributesMap.containsKey(campaignId)){
        // the list in the value already exists anyway, just add a new cell user number to it 
        cellAttributesMap.get(campaignId).add(cellUserNumber);
    }
    else {
        // create a new key-value pair in the result map
        // and add one element which is a current cellUserNumber to it
        List<Long> cellList = new ArrayList<>();
        cellList.add(cellUserNumber);
        cellAtributesMap.put(campaignId, cellList);
    }
}
return cellAtributesMap;