When an Object becomes Eligible for Garbage Collection
An Object becomes eligible for Garbage collection or GC if its not reachable from any live threads or any static refrences in other words you can say that an object becomes eligible for garbage collection if its all references are null. Cyclic dependencies are not counted as reference so if Object A has reference of object B and object B has reference of Object A and they don’t have any other live reference then both Objects A and B will be eligible for Garbage collection.
Generally an object becomes eligible for garbage collection in Java on following cases:
1) All references of that object explicitly set to null e.g. object = null
2) Object is created inside a block and reference goes out scope once control exit that block.
3) Parent object set to null, if an object holds reference of another object and when you set container object’s reference null, child or contained object automatically becomes eligible for garbage collection.
4) If an object has only live references via WeakHashMap it will be eligible for garbage collection. To learn more about HashMap see here How HashMap works in Java.