语法：
class 比较器名 implements Comparator
重写 int compare(Object o1, Object o2)

import java.util.*;class comparatorDemo implements Comparator {public int compare(Object o1, Object o2) {String a, b;a = (String) o1;b = (String) o2;return b.compareTo(a); // 从大到小排序// return a.compareTo(b); // 从小到大排序}
}// 以有序set、有序map为例
class test6{public static void main(String[] args){TreeSet ts = new TreeSet(new comparatorDemo());//传入比较器ts.add("C");ts.add("A");ts.add("D");Iterator it = ts.iterator();while(it.hasNext()){Object o = it.next();System.out.println(o);} // D C AString a = "Aaaab", b = "A";System.out.println(a.compareTo(b)); // 4, a > b 正数TreeMap tm = new TreeMap(new comparatorDemo());tm.put("Michael", 18);tm.put("Ming", 18);tm.put("ABC", 19);Set set = tm.entrySet();Iterator it1 = set.iterator();while(it1.hasNext()){Object o = it1.next();System.out.println(o);}// Ming=18// Michael=18// ABC=19}
}