public static int random() {
    TreeMap<Integer, Integer> map = new TreeMap<Integer, Integer>();
    map.put(0, 0);
    map.put(7, 1);
    int ran = (int)(System.currentTimeMillis()%10);
    return map.lowerEntry(ran).getValue().intValue();
}

if (random() == 0) {
    System.out.println("do A");
} else {
    System.out.println("do B");
}