spooler.java

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public class Spooler {
    //this is a prototype for a printer-spooler class
    //such that only one instance can ever exist
    static boolean instance_flag=false; //true if 1 instance

    public Spooler() throws SingletonException
    {
        if (instance_flag)
            throw new SingletonException("Only one printer allowed");
        else
            instance_flag=true;     //set flag for 1 instance
        System.out.println("printer opened");
    }
  
}