Island of Isolation in Java
Last Updated :
12 Dec, 2021
In Java, object destruction is taken care of by the garbage Collector module and the objects which do not have any references to them are eligible for garbage collection. Garbage Collector is capable to identify this type of object. Now let us do discuss what the exactly Island of Isolation stands for as follows:
- Object 1 references Object 2 and Object 2 references Object 1. Neither Object 1 nor Object 2 is referenced by any other object. That’s an island of isolation.
- Basically, an island of isolation is a group of objects that reference each other but are not referenced by any active object in the application. Strictly speaking, even a single unreferenced object is an island of isolation too.
Example:
Java
public class GFG {
GFG i;
public static void main(String[] args)
{
GFG t1 = new GFG();
GFG t2 = new GFG();
t1.i = t2;
t2.i = t1;
t1 = null;
t2 = null;
System.gc();
}
@Override protected void finalize() throws Throwable
{
System.out.println("Finalize method called");
}
}
|
Output:
Output Explanation:
- Before destructing an object, Garbage Collector calls finalize method at most one time on that object. It is because finalize() method is called two times in the above example is because two objects are eligible for garbage collection. This is because we don’t have any external references to t1 and t2 objects after executing t2=null.
- All we have is only internal references(which is in instance variable i of class Test) to them of each other. There is no way we can call instance variable of both objects. So, none of the objects can be called again till ‘t2.i = t1‘
- Both the objects have external references t1 and t2.
- t1 = null : Both the objects can be reached via t2.i and t2 respectively.
- t2 = null: No way to reach any of the objects.
Now, both the objects are eligible for garbage collection as there is no way we can call them. This is popularly known as Island of Isolation.
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