spooler.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 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");
    }
  
}