小技巧：set的排序

这里有个例子是关系set的排序

import java.util.Arrays;
import java.util.Comparator;
import java.util.HashSet;
import java.util.Set;
import java.util.TreeSet;

import com.itextpdf.text.log.SysoCounter;


public class test7 {

    public static void main( String[] args ) {
        Set<String> set = new   HashSet <>();
        set.add("201801");
        set.add("201803");
        set.add("201802");
        set.add("201805");
        set.add("201808");
        set.add("201807");
       // setSort(set);
       
      System.out.println("顺序"+setSort(set,"des"));    
      System.out.println("倒序"+setSort(set,"desc"));    
 
    }

    //set排序 set对象，排序des或空顺序，desc倒序
    public static Set<String>  setSort(Set<String>  set,String orderby){
        Set<String> newSet=new HashSet<>();
        if(orderby.equals("")||orderby.equals("des")){//顺序
             newSet = new TreeSet<String>();
            for(String str:set){
                newSet.add(str);
            }
        }

        if(orderby.equals("")||orderby.equals("desc")){//倒叙
             newSet = new TreeSet<String>(new MyComparator());
            for(String str:set){
                newSet.add(str);
            }
        }
             
        return newSet;
        
    }
    
    
    

}



class MyComparator implements Comparator<String>{
     
@Override
public int compare(String o1, String o2) {
 
return o2.compareTo(o1);//降序排列
}
 
}