Garbage Collection Certification - finalize()

Syntax (JDK 1.3)

    protected void finalize() throws Throwable {}

• every class inherits the finalize() method from java.lang.Object
• the method is called by the garbage collector when it determines no more references to the object exist
• the Object finalize method performs no actions but it may be overridden by any class
• normally it should be overridden to clean-up non-Java resources ie closing a file
• if overridding finalize() it is good programming practice to use a try-catch-finally statement and to always call super.finalize() (JPL pg 47-48). This is a saftey measure to ensure you do not inadvertently miss closing a resource used by the objects calling class

protected void finalize() throws Throwable {
    try {
        close();        // close open files
    } finally {
        super.finalize();
    }
}

• any exception thrown by finalize() during garbage collection halts the finalization but is otherwise ignored
• finalize() is never run more than once on any object

Also see

• Object finalization and cleanup - JavaWorld, June 1998
• Sun Tech Tip: Using finally versus finalize to guarantee quick resource cleanup

Example Code

• TestGC.java