JavaSE 学习参考：TreeSet

TreeSet类内部采用的二叉树数据结构，默认使用元素的自然排序接口Comparable对元素进行排序,也可以在构造时指定排序器Comparator来指定排序规则。

例如若将自定义Student类的对象放置到TreeSet中，按照姓名字典顺序排序，可以采用两种方式实现。

Comparable接口

让Student类实现Comparable接口，重写compareTo(Student)方法，在方法定义排序规则。

Comparator接口

定义排序器类实现Comparator接口，重写compare(Student s1,Student s2)方法，在方法定义排序规则,在构造TreeSet实例时传入排序器类实例。。

示例： class Student implements Comparable<Student>{ private String name; private int age; private double score; public Student(String name, int age, double score) { super(); this.name = name; this.age = age; this.score = score; } public String getName() { return name; } public void setName(String name) { this.name = name; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } public double getScore() { return score; } public void setScore(double score) { this.score = score; } @Override public int compareTo(Student s) { return 0; } @Override public String toString() { return "Student [name=" + name + ", age=" + age + ", score=" + score + "]"; } } class StudentScoreComparator implements Comparator<Student>{ @Override public int compare(Student s1, Student s2) { return (int)(s1.getScore()*100-s2.getScore()*100)/100; } } public class Test { public static void main(String[] args) { Set<String> set=new HashSet<String>(); set.add("Tom"); set.add("Alice"); set.add("Martin"); set.add("Jerry"); Iterator<String> it=set.iterator(); while(it.hasNext()){ String city=it.next(); System.out.println(city); } } }