我对object2objectopenhashmap有一个问题，当我使用put方法时，java给我这个异常“nullpointerexception”。
代码如下：

private Object2ObjectOpenHashMap level1 = new Object2ObjectOpenHashMap();
private Object2ObjectOpenHashMap level0 = new Object2ObjectOpenHashMap();

public void map(Object ke, Text val, Context context) throws IOException, InterruptedException {

        Configuration conf = context.getConfiguration();
        int numberAttributes = conf.getInt("numberAttributes", 0);
        String jsoncombinationlevel0 = conf.get("combinationlevel0");
        String jsonopenlevel0 = conf.get("openlevel0");
        String jsoncombinationlevel1 = conf.get("combinationlevel1");

        ArrayList<OpenBitSet> open1ArrayList = new Gson().fromJson(val.toString(), new TypeToken<ArrayList<OpenBitSet>>(){}.getType());
        ArrayList<OpenBitSet> open0ArrayList = new Gson().fromJson(jsonopenlevel0.toString(), new TypeToken<ArrayList<OpenBitSet>>(){}.getType());
        ArrayList<CombinationHelper> chLevel0 = new Gson().fromJson(jsoncombinationlevel0.toString(), new TypeToken<ArrayList<CombinationHelper>>(){}.getType());   
        ArrayList<CombinationHelper> chLevel1 = new Gson().fromJson(jsoncombinationlevel1.toString(), new TypeToken<ArrayList<CombinationHelper>>(){}.getType());   

        //ricostruisco level1
        int i=0;
        for(OpenBitSet x : open1ArrayList) {
            level1.put(x, chLevel1.get(i)); 
            i++;

        }
    //other stuff
    .
    .
    .}

所以，当代码到达for时，我使用put方法java给我一个异常：

Caused by: java.lang.NullPointerException at hadoop.InitializeCplusForLevelMapReduce$MapperInitializeCplusForLevel.map(InitializeCplusForLevelMapReduce.java:78)

78号线在哪

level1.put(x, chLevel1.get(i));

我不知道为什么，这似乎是正确的，我想创建level1，并为相对数组列表中的每个openbitset我想把它与相对combinationhelper放在level1。我只找到了方法，我试过其他方法，但都是一样的，一样的例外。