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 = newHashSet <>();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);}} retu newSet;}}class MyComparator implements Comparator<String>{ @Overridepublic int compare(String o1, String o2) { retu o2.compareTo(o1);//降序排列} }