程序题:

如下代码会如何进行输出:

    public static void main(String[] args) {
        HashMap<Object, Object> map = Maps.newHashMap();
        map.put("1", null);
        map.put("2", null);
        Collection<Object> values = map.values();
        System.out.println(values);
        values.remove(null);
        System.out.println(values);
        System.out.println(values.size());
        values.remove(null);
        System.out.println(values);
        System.out.println(values.size());

    }

输出:

[null, null]
[null]
1
[]
0

---

结果出乎我的意料,

起因:

第一次异常信息:

java.lang.NullPointerException
        at java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:193) ~[?:1.8.0_73]
        at java.util.HashMap$ValueSpliterator.forEachRemaining(HashMap.java:1612) ~[?:1.8.0_73]
        at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:481) ~[?:1.8.0_73]
        at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:471) ~[?:1.8.0_73]
        at java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:708) ~[?:1.8.0_73]
        at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234) ~[?:1.8.0_73]
        at java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:499) ~[?:1.8.0_73]
        at com.ejlerp.pms.provider.service.UniqueCodeServiceImpl.translateSkuInfo(UniqueCodeServiceImpl.java:78) ~[?:?]

第一次bugfix:

image.png

无效果依旧报错

java.lang.NullPointerException
    at com.ejlerp.pms.provider.service.UniqueCodeServiceImpl.lambda$translateSkuInfo$111(UniqueCodeServiceImpl.java:81) ~[?:?]
    at java.util.stream.ReferencePipeline$2$1.accept(ReferencePipeline.java:174) ~[?:1.8.0_73]
    at java.util.HashMap$ValueSpliterator.forEachRemaining(HashMap.java:1612) ~[?:1.8.0_73]
    at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:481) ~[?:1.8.0_73]
    at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:471) ~[?:1.8.0_73]
    at java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:708) ~[?:1.8.0_73]
    at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234) ~[?:1.8.0_73]
    at java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:499) ~[?:1.8.0_73]
    at com.ejlerp.pms.provider.service.UniqueCodeServiceImpl.translateSkuInfo(UniqueCodeServiceImpl.java:81) ~[?:?]

第二次bugfix:

image.png

第三次bugfix:

image.png

结论:

需要探究HashMap的内部实现,待补充