多例模式实现编码器(格式：编码字符+3位递增数字)

[c#]代码库

public class ProductCoder
{
 static Hashtable coders=new Hashtable();
 private int _number;
 private string _prefix="";
 private ProductCoder(){}

 public static ProductCoder Instance(string prefix){
      ProductCoder p=null;
      if(coders.Contains(prefix)){
         p=(ProductCoder)coders[prefix];
     }
     else lock(coders){
        p=new ProductCoder();
        p._prefix=prefix;
        coders.Add(prefix,p);
     }
    return p;
     
  }
  public string Prefix{
    get{return _prefix;}
  }
  public string GetNewCode(){
     return(string.Format("{0}{1:000}",_prefix,++_number));
   }
  public string GetLastCode(){
      return (string.Format("{0}{1:000}",_prefix,++_number));
  }
}