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copied!<p>All this behaviour is implementation dependent. The garbage collector runs in its own asynchronous thread that has nothing to do with the synchronization behavior of your program. You simply do not know when the array referenced by data1 will be garbage collected -- you can only hope that it will happen in a "reasonable" amount of time after it goes out of scope/all references to it are gone.</p> <p>If you are worried about running out of memory in your program, you can explicitly attempt to trigger a garbage collection cycle with System.gc(). But even this does not guarantee that enough memory will be available when you allocate data2. Calling System.gc() is simply a hint to the runtime that you'd like a garbage collection cycle now.</p> <p>In Java, memory allocation and deallocation is non-deterministic. The garbage collector will run when it runs and you can't make it run at the program level. There's no relevant differences between the code snippets you posted, because gc behaviour is non-deterministic and the precise moment at which it is triggered is implementation and system dependent. Sometimes this is a problem for your application -- if it's an OS or runs in a memory constrained embedded device, for example -- and you will need to code in C++ or some other language where memory management is deterministic. For most of us, though, we just trust that the garbage collector will behave in a reasonably reasonable manner and that is good enough for most purposes -- although, as you see, you can create contrived code that causes problems.</p> <p>Update: Embarrassing. As a couple of other commenters have reminded me, a garbage collection cycle is explicitly triggered before the jvm throws an OutOfMemory error. However, the behaviour is still non-deterministic: as <a href="http://java.sun.com/javase/technologies/hotspot/gc/gc_tuning_6.html" rel="nofollow noreferrer">this link</a> explains, the jvm does not guarantee that all dead objects will be detected in one garbage collection cycle.</p>

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