In Java, when does an object become unreachable?

Question

In Java, what is an unreachable object? When does the object become unreachable? While studying garbage collection I was not able to understand this concept.

Can anyone give any ideas with examples?

Answer 1

When there are no longer any reference variables referring to it, OR when it is orphaned in an island.

An island being an object that has a reference variable pointing to it, however that object has no reference variables pointing to it.

class A { int i = 5; } class B { A a = new A(); } class C {    B b;    public static void main(String args[]) {       C c = new C();       c.b = new B();       // instance of A, B, and C created       c.b = null;       // instance of B and A eligible to be garbage collected.    } 

EDIT: Just want to point out that even though the instance of A has a reference, it is on an island now because the instance of B does not have a reference to it. The A instance is eligible for garbage collection.