code: public static String generateMixPassword(final int n) {
  		final char[] pw = new char[n];
  		int c = 'A';
  		int r1 = 0;
  		for (int i = 0; i < n; i++) {
  			r1 = (int) (Math.random() * 3);
  			switch (r1) {
  			case 0:
  				c = '0' + (int) (Math.random() * 10);
  				break;
  			case 1:
  				c = 'a' + (int) (Math.random() * 26);
  				break;
  			case 2:
  				c = 'A' + (int) (Math.random() * 26);
  				break;
  			}
  			pw[i] = (char) c;
  		}
  		return new String(pw);
  	}
docs: //////////////////////////////////////////////////////////