ArrayList creation: (some object) cannot be stored in an array of type java.lang.Object[]

Question

Usually, the code block works perfect. On very rare occasions though, the "new ArrayList" throws an Exeption my.namespace.CacheEntry cannot be stored in an array of type java.lang.Object[].

Checking Google, someone else seemed to get this exception on an Acer A500 with 3.1 (which is the device I got it, too). I don't see any hit for this in generic Java or whatever, so may be some very very Honeycomb special case or even a VM bug?

private long expireCache(HashMap<String, CacheEntry> map) {
    long count = 0;
    // next line will sometimes throw the exception:
    ArrayList<CacheEntry> entries = new ArrayList<CacheEntry>(map.values());
    Collections.sort(entries);

The CacheEntry class is quite regular, too:

final class CacheEntry implements Comparable<CacheEntry> {
    public File file;
    public Long time;

    CacheEntry(File cacheFile) {
        // retreive the lastModified only once, don't do heavy I/O for sorting,
        // keep it desynced from filesystem so nothing bad happens when the 
        // file gets changed while sorting:
        file = cacheFile;
        time = cacheFile.lastModified();
        }

     // "touch" the cached last modified time
     public void touch() {
        time = System.currentTimeMillis();
        }

     // return the long comparable of last modified time
     public int compareTo(CacheEntry c) {
        return time.compareTo(c.time);
        }
     }

I don't see anything wrong with this code. Anyone?

Where and how do you invoke expireCache? Give example please. — Alexandr
– Alexandr, Commented Sep 13, 2011 at 10:58
Your code seems correct, it looks like a Honeycomb bug indeed. — Guillaume
– Guillaume, Commented Sep 13, 2011 at 10:59
@Alexandr, I think it totally doesn't matter for this problem when and how this function gets called. But if you really need to know, it gets called from inside a syncronized(cacheentry-hashmap) entry (as all changes to the hashmap are inside synchronized), when the size of the cache or the number of elements in the map are over a highwater mark. — Oliver
– Oliver, Commented Sep 13, 2011 at 11:12

Michael Borgwardt · Accepted Answer · 2011-09-13 11:03:36Z

2

may be some very very Honeycomb special case or even a VM bug?

Yes, looks like it, because according to Java semantics, there isn't anything that "cannot be stored in an array of type java.lang.Object[]" - except primitives, but those can't be values in a HashMap

answered Sep 13, 2011 at 11:03

Michael Borgwardt

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