ispooler.java

源码为科学出版社出版的英文<java设计模式>(影印版)所用的所有例子程序

public class iSpooler {
    //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

    private iSpooler() {
    }      //private constructor

    public static synchronized iSpooler Instance() {
        if (! instance_flag) {  //only allow one instance
            instance_flag = true;
            return new iSpooler();
        } else
            return null;         //or return none
    }
    //-------------------------------------------
    public void finalize() {
        instance_flag = false;
    }
}