How can I prevent class garbage collection????

Question

Hi,
Is there a way to prevent a class from being garbage collected without using the -noclassgc option? Is there some code I can include in a class that tells the JVM not to garbage collect that particular class?
Thanks in advance,
Jacob.

Answer 1

The code shown below (slightly modified from yours) should work correctly on any 1.0.x throught 1.4 JVM.
Look at this article for further info: http://www.javaworld.com/javaworld/javatips/jw-javatip52.html
public class SQLManager extends PoolManager {
    private static SQLManager myself;
    //code.........................
    public static SQLManager getInstance() {
        // This version of a getInstance method suffers from the use of the
        // broken (unreliable) double checked locking idiom.  It should never
        // be used on a system with more than one processor and is ill-advised
        // any other time.  It can  lead to accesses to uninitialized objects.
        // See http://www.javaworld.com/javaworld/jw-02-2001/jw-0209-double.html
        // or http://c2.com/cgi/wiki?DoubleCheckedLockingIsBroken
        // So despite its common appearance in books and pattern repositories,
        // it should not be used.
        if (myself == null) {
            synchronized(SQLManager.class) {
                if (myself == null)
                    myself = new SQLManager();
        return myself;
    private SQLManager() {
        livethread();
        //code.........................
    void livethread()
        System.out.println("##############################################################");
        System.out.println("###################Live Thread called#########################");
        System.out.println("##############################################################");
        Thread thread = new Thread()
            public void run()
                // added this code to ensure that run() actually is getting
                // called
                System.out.println("##############################################################");
                System.out.println("#################### Thread Started ##########################");
                System.out.println("##############################################################");
                Class myClass = SQLManager.class;
                while (true)
                    try
                        synchronized (myClass)
                            myClass.wait();
                    catch (InterruptedException ex)
                        System.out.println("##############################################################");
                        System.out.println("###################Thread interrupted#########################");
                        System.out.println("##############################################################");
                    finally
                        System.out.println("##############################################################");
                        System.out.println("################### Something Happened #########################");
                        System.out.println("##############################################################");
                System.out.println("##############################################################");
                System.out.println("#################### Thread Dead?? ##########################");
                System.out.println("##############################################################");
        thread.setDaemon(true);
        System.out.println("##############################################################");
        System.out.println("#################### Starting Thread #########################");
        System.out.println("##############################################################");
        thread.start();
    //code.........................
}