Should i use finalize() or not in java? [duplicate]

Question

Why execution of finalize() isn't guaranteed at all in Java? Is finalize() method shouldn't be used???

Consider below program.

class Test{
   protected void finalize()
   {
       System.out.println("Will i execute?");
   }
   public static void main(String args[])
   {
         Test t=new Test();
   }
}

There is an empty output when this program runs. We know that finalize() is used to cleanup any external resources before the object becomes eligible for garbage collection & finalize() will be called by JVM. Inside finalize() we will specify those actions that must be performed before an object is destroyed. Is finalize() method evil??

Answer 1

Javadoc link, because many quotes will follow.

We know that finalize() is used to cleanup any external resources before the object becomes eligible for garbage collection

No. Once the object becomes eligible for garbage collection, then finalize() can get invoked. finalize could theoretically make the object no longer eligible for garbage collection and the garbage collector would then skip it. As stated

After the finalize method has been invoked for an object, no further action is taken until the Java virtual machine has again determined that there is no longer any means by which this object can be accessed by any thread that has not yet died

Why execution of finalize() isn't guaranteed at all in Java?

It is guaranteed to run. As the Javadoc states

The general contract of finalize is that it is invoked if and when the Java™ virtual machine has determined that there is no longer any means by which this object can be accessed by any thread that has not yet died, except as a result of an action taken by the finalization of some other object or class which is ready to be finalized.

What isn't guaranteed is when or if garbage collection will occur.

Should i use finalize() or not in java?

That depends on your use case. Start by reading the javadoc and understand the implications.