String[] strArray = {"0", "1", "2", "3", "4", "5", "6", "7", "8", "9"};
int codeCount = 4;
StringBuffer code = new StringBuffer();
for(int i=0; i<codeCount; i++) {
code.append(strArray[(int) (Math.random()*10)]);
}
System.out.println(code);
原文：http://www.cnblogs.com/loveflycforever/p/5862401.html