Using Shutdown Hook

rossum <>
Sun, 25 Nov 2007 12:46:39 +0000
Thanks to all of you who responded to my thread on replacing

David Roden suggested using a Shutdown Hook. Never having used one
before I put together a simple test program, (below), which seems to
work. Have I made any mistakes in this? Any pointers to improvements
would be helpful.

Thanks in advance,


// --- Begin Code ---

import java.lang.ref.WeakReference;

 * Testing Shutdown Hook
public class HookTester {
    private double mSecret;

    public HookTester() {
        mSecret = Math.random();
        // Set up ShutdownHook in constructor
        ShutdownHook sdh = new ShutdownHook(
            new WeakReference<HookTester>(this));
        Runtime.getRuntime().addShutdownHook(new Thread(sdh));
    public void dispose() {
        System.out.println("Running dispose()");
        mSecret = 0.0;
        System.out.println("Secret deleted.");

    protected void finalize() {
        System.out.println("Running finalize()");

    class ShutdownHook implements Runnable {
        // Use a weak reference so as not to delay garbage collection.
        private WeakReference<HookTester> mWeakRef;
        public ShutdownHook(WeakReference<HookTester> wRef) {
            mWeakRef = wRef;
        public void run() {
            if (mWeakRef.get() != null) {
    public static void main(String[] args) {
        HookTester ht = new HookTester();
        // ht.dispose() not explicitly called.

// --- End Code ---

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