How can I create a memory leak in Java?

Question

I just had an interview, and I was asked to create a memory leak with Java.

Needless to say, I felt pretty dumb having no clue on how to eve

Answer 1

I have had a nice "memory leak" in relation to PermGen and XML parsing once. The XML parser we used (I can't remember which one it was) did a String.intern() on tag names, to make comparison faster. One of our customers had the great idea to store data values not in XML attributes or text, but as tagnames, so we had a document like:

   <1>bla
   <2>foo
   ...

In fact, they did not use numbers but longer textual IDs (around 20 characters), which were unique and came in at a rate of 10-15 million a day. That makes 200 MB of rubbish a day, which is never needed again, and never GCed (since it is in PermGen). We had permgen set to 512 MB, so it took around two days for the out-of-memory exception (OOME) to arrive...