一、创建TreeSet实例

public static void main(String[] args) {

TreeSet set = new TreeSet();

set.add("C");

set.add("B");

set.add("A");

set.add("F");

set.add("D");

System.out.println(set);

}

输出

[A, B, C, D, F]

输出是有序的。

二、TreeSet实例，按字符倒叙排列

实现了Comparator接口

public class TreeSetTest3 {

public static void main(String[] args) {

TreeSet set = new TreeSet(new MyComparator() );

set.add("C");

set.add("B");

set.add("A");

set.add("F");

set.add("D");

System.out.println(set);

}

}

class MyComparator implements Comparator{

public int compare(Object o1, Object o2) {

String s1 = (String) o1;

String s2 = (String) o2;

return s2.compareTo(s1);

}

}

打印：

[F, D, C, B, A]

三、按数字倒叙排列

public class TreeSetTest2 {

public static void main(String[] args) {

TreeSet set= new TreeSet(new Comparator() {

public int compare(Object o1, Object o2) {

int i1 = ((Person) o1).score;

int i2 = ((Person) o2).score;

return i2 - i1;

}

});

Person p1 = new Person(100);

Person p2 = new Person(60);

Person p3 = new Person(70);

Person p4 = new Person(50);

set.add(p1);

set.add(p2);

set.add(p3);

set.add(p4);

System.out.println(set);

}

}

class Person{

int score;

public Person(int score){

this.score = score;

}

@Override

public String toString() {

return String.valueOf(this.score);

}

}

打印结果

[100, 70, 60, 50]

四、使用Collections降序

public class CollectionsTest {

public static void main(String[] args) {

LinkedList list = new LinkedList();

list.add(new Integer(5));

list.add(new Integer(25));

list.add(new Integer(15));

list.add(new Integer(35));

list.add(new Integer(1));

Comparator r = Collections.reverseOrder();

Collections.sort(list, r);

System.out.println(list);

}

}

[35, 25, 15, 5, 1]