Project Coin: Inducing contributory heap pollution

Joe Darcy joe.darcy at
Thu Jun 10 19:50:23 PDT 2010

Reinier Zwitserloot wrote:
> As I've mentioned before in regards to this topic, there's a list of 
> things you can do to a potentially polluted array that are perfectly 
> safe (or at least as safe as anything else with generics is):
> 1. ask for its length: param.length
> 2. iterate over it in a foreach: for (Whatever x : param) { ... }
> 3. read (not write) a value from it: Whatever x = param[whatever];
> 4. use it as parameter to another method where that parameter is also 
> marked as "polluted array safe" - e.g. @SuppressWarnings("varargs"). 
> For example, if Arrays.asList() is given the marker (which it should, 
> nothing bad happens), then calling Arrays.asList(param) can't result 
> in bad things either.
Just noting that given the defined semantics of the for-each loop on an 
array, point 2 would be implied by points 1 and 3; although it is good 
to call out separately.

A good start at validating such rules is looking at the implementations 
of the JDK methods where the TrustMeOnVarargs annotation would be 
helpful; iterating over the elements in a for-each loop and passing the 
array along as a method parameter are the operations that occur in the 
three methods.


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