Java实现id自增的字符串类型的数字编号

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一些id标识的要求，比如数字自增，0001，0002，0003等。下面这个方法实现了这个功能：

思路：int a；a++；fillstr（）；

贴代码：

public class mainTest {  public static void main(String[] args) {  String outString="";  outString=fillStr("123", 9, false, "0");  System.out.println("false"+outString);  outString=fillStr("123", 9, true, "0");  System.out.println("true"+outString);   } /**  *   * @param value  * @param count  * @param frontORback   * @param fillChar  * @return if frontORback is ture ,return the (count-value.length) fillchar added to the front of the value   * if frontORback is false,return the (count-value.length) fillchar added to the back of the value  * for instance : value="123",count=9,frontORback=true,fillchar="0"<br>  * return "123000000"  *  */ private static String fillStr(String value, int count, boolean frontORback, String fillChar) {     String rtvalue = value;     if (rtvalue == null) {      rtvalue = "";      for (int i = 0; i < count; i++)       if (frontORback)        rtvalue = String.valueOf(rtvalue)          + String.valueOf(fillChar);       else        rtvalue = String.valueOf(fillChar)          + String.valueOf(rtvalue);     } else {      int len = rtvalue.length();      if (len > count) {       rtvalue = rtvalue.substring(0, count);      } else {       int a = count - len;       for (int i = 0; i < a; i++)        if (frontORback)         rtvalue = String.valueOf(rtvalue)           + String.valueOf(fillChar);         else         rtvalue = String.valueOf(fillChar)           + String.valueOf(rtvalue);      }     }     return rtvalue;    }}