Java_隨機生成4位驗證碼

import java.util.*;//導入java.util包下的類 public class JavaDemo10 { public static void main(String args[]) { String str = "0,1,2,3,4,5,6,7,8,9,a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q,r,s,t,u,v,w,x,y,z,A,B,C

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