（69）TreeSet练习：按照长度为主关键字，自然顺序为次关键字排序

import java.util.*;

public class StringCompare implements Comparator{

public int compare(Object o1,Object o2) {

String str1=(String)o1;
String str2=(String)o2;
int num=str1.length()-str2.length();//主关键字
if(num==0) {
return str1.compareTo(str2);//次关键字
}
return num;
}
}

public class StringDemo {

public static void main(String[] args) {
// TODO Auto-generated method stub
TreeSet ts=new TreeSet(new StringCompare());

ts.add("lisi00");
ts.add("lisi001");
ts.add("lisi02");
ts.add("lisi0");
ts.add("lisi04");

Iterator it=ts.iterator();
while(it.hasNext()) {
Object obj=it.next();
String str=(String)obj;
System.out.println(str);

}
}

}