Something

StringBuilder sb = new StringBuilder();
for (int x : a) {
   if (x == ret[0] || x == ret[1] || x == ret[2] || x == ret[3]) {
      sb.append(':').append(x).append(':');
      }
   } else {
      sb.append(' ').append(x).append(' ');
   }
}
System.out.println(sb.toString());