garbage collection

[Isabel Wanderley]

Can anyone comment this affirmatives for me? Saying if they're true or false and why?
a) The garbage collector can be invoked explicitly using a Runtime object.
b) The finalize method is always called before an object is garbage collected.
c) Any class that includes a finalize method should invoke its superclass' finalize method.
d) Garbage collection behavior is very predictable.

[Anthony Villanueva]

Hi Isabel,
A good explanation of garbage collection can be found here.
1. According to the docs, the method

public static void gc()
Runs the garbage collector.
Calling the gc method suggests that the Java Virtual Machine expend effort toward recycling unused objects in order to make the memory they currently occupy available for quick reuse. When control returns from the method call, the Java Virtual Machine has made a best effort to reclaim space from all discarded objects.
The call System.gc() is effectively equivalent to the call:
Runtime.getRuntime().gc()

2 and 3. Yes and yes.
See this thread.
4. It depends on the JVM implementation.

[Ron Newman]

The finalize() method is always called once before the object is garbage-collected.
But if the finalize() method makes the object reachable again and therefore prevents garbage-collection, the finalize() method will not be called again the next time the object becomes unreachable and is garbage-collected.
I don't know why Java works this way -- maybe someone else can explain the rationale.

[Jose Botella]

The finalize method was intended to carry out clean up operations others than memory's ones. This clean up should happen only once per object.
However it isn't recommended to use the finalize method because we are not certain of its execution. In order to clean up resources call a normal instance method in the object just before setting its references to null.