Complex Comparator

A comparator can use if statements to compare two objects using multiple criteria, e.g. year first, then month, then day.

Comparator<MyDate>
 cmp = new Comparator<MyDate>() {
  public int compare(MyDate x, MyDate y) {
      int ans = x.year - y.year;
      if (ans != 0) return ans;
      ans = x.month - y.month;
      if (ans != 0) return ans;
      return x.day - y.day; }};

int res = cmp.compare(datea, dateb);

Sometimes it is convenient for the comparator to simply return a value such as 1 or -1 to indicate that one object should be sorted before the other.