Question

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Garbage Collection in Java and Circular References

Java runs it’s garbage collector whenever there is not enough space in the memory . It does so by deleting the unreferenced objects. So what if an object has a pointer that points to itself ,or any cyclic pointing structure that always has a pointer to it ? Will the garbage collector fail or will it recognize any such insidious attempts made by us in order to make it fail ?

Answer 1

Whether the objects will be collected depends on the Garbage collecting algorithm

• reference-counting GC, will not collect cyclic references
• but, modern GC algorithms usually decide eligibility of an object for collection by traversing the heap starting from the root set.

Garbage collector will collect objects that are not accessible from the root set of references (current local variables, static references, operand stacks of stack frames). This means that even objects that are referenced by some other objects can still be collected.

Therefore, your cyclic-pointer structure will get collected even though each object is referenced iff there is no other reference path going transitively from the root set to the objects forming the cycle.

See also What triggers the Java Garbage Collector.