TreeSet

TreeSet

1. TreeSet是依靠TreeMap来实现的；
2. TreeSet是一个有序集合，TreeSet中元素将按照升序排列，缺省是按照自然顺序进行排列，意味着TreeSet中元素要实现Comparable接口；
3. 我们可以在构造TreeSet对象时，传递实现了Comparator接口的比较器对象；
4. HashSet和TreeSet的比较
   
   1. HashSet是基于Hash算法实现的，其性能通常都优于TreeSet。我们通常都应该使用HashSet。在我们需要排序的功能时，我们才使用TreeSet；

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import java.util.*;
class TreeSetTest{
    public static void main(String[] arg){
        TreeSet ts = new TreeSet(new Students.StudentCompare());
        ts.add(new Students(11,"zhangsan"));
        ts.add(new Students(14,"wangwu"));
        ts.add(new Students(10,"lisi"));
        ts.add(new Students(11,"ihangsan"));

        Iterator it = ts.iterator();
        while(it.hasNext()){
            System.out.println(it.next());
        }
    }
}

class Students{
    int num;
    String name;
    Students(int num,String name){
        this.num = num;
        this.name = name;
    }
    static class StudentComparator implements Comparator{
        public int compare(Object o1,Object o2){
            Students s1 = (Students)o1;
            Students s2 = (Students)o2;
            int result = s1.num > s2.num ? 1 : s1.num == s2.num ? 0 : -1;
            if(result == 0){
                result = s1.name.compareTo(s2.name);
            }
            return result;
        }
    }
    public String toString(){
        return "num="+num+"name="+name;
    }
}