TreeSet的两种排序方法：自然排序和定义比较器，推荐使用定义比较器方法。
<span style="color:#333333;">import java.util.*;
class treeset
{
public static void main(String[] args)
{
TreeSet t = new TreeSet();
// TreeSet t = new TreeSet(new mycomparator());//第二种方法定义
t.add(new student("a1",18));
t.add(new student("a2",18));
t.add(new student("a1",18));
t.add(new student("a3",16));
t.add(new student("a4",25));
for(Iterator it = t.iterator();it.hasNext();)
{
student s = (student)it.next();
sop(s.getName()+","+s.getAge());
}
}
public static void sop(Object obj)
{
System.out.println(obj);
}
}
/*
自然排序法 定义Comparable接口，覆盖CompareTo方法
*/
class student implements Comparable
{
private String name;
private int age;
student(String name,int age)
{
this.name = name;
this.age = age;
}
public int compareTo(Object obj)
{
if(!(obj instanceof student))
throw new RuntimeException("不是学生");
student s = (student)obj;
if(this.age>s.age)
return 1;
if(this.age==s.age)
return this.name.compareTo(s.name);
return -1;
}
public String getName()
{
return name;
}
public int getAge()
{
return age;
}
}
/*
定义比较器 当两种方法都存在时，以比较器为主。
定义一个类，实现Comparator接口，覆盖compare方法
*/
class mycomparator implements Comparator
{
public int compare(Object o1,Object o2)
{
student s1 = (student)o1;
student s2 = (student)o2;
int num = s1.getName().compareTo(s2.getName());
if(num ==0)
{
if(s1.getAge()>s2.getAge())
return 1;
if(s1.getAge()==s2.getAge())
return 0;
return -1;
}
return num;
}
}</span>
