Java基础Day-Sixteen

应用Collection实现集合排序

package com.imooc.collection.List;
​
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
​
public class ListSorter {
​class SampleComparator implements Comparator<Integer>{//70 90 30 50//结果>0，则交换位置//结果=0或小于0，则位置不变@Overridepublic int compare(Integer o1, Integer o2) {return o2-o1;//o1-o2：升序；o2-o1：降序}}
​public List<Integer> sort(List<Integer> list){Collections.sort(list,new SampleComparator());//升序排列System.out.println(list);return list;}
​public static void main(String[] args) {List<Integer> list=new ArrayList<>();list.add(70);list.add(90);list.add(30);list.add(50);System.out.println(list);ListSorter listSorter=new ListSorter();List<Integer> list1=listSorter.sort(list);System.out.println(list1);}
}

• 自定义类型如何集合排序

  package com.imooc.collection;
  ​
  public class Goods {private String sn;private String title;
  ​public Goods(String sn,String title){this.title=title;this.sn=sn;}
  ​@Overridepublic String toString(){return "Goods{"+"sn='"+sn+'\''+",title='"+title+'\''+'}';}
  ​public String getSn(){return sn;}
  ​public String getTitle(){return title;}
  }
  ​

  package com.imooc.collection;
  ​
  import java.util.ArrayList;
  import java.util.Collections;
  import java.util.Comparator;
  import java.util.List;
  ​
  public class CustomObjectSortSample {private class CustomComparator implements Comparator<Goods>{
  ​@Overridepublic int compare(Goods o1, Goods o2) {
  //            return o1.getSn().compareTo(o2.getSn());return o1.getTitle().compareTo(o2.getTitle());}}
  ​public List<Goods> sort(List<Goods> list){CustomComparator comp=new CustomComparator();Collections.sort(list,comp);return list;}
  ​public static void main(String[] args) {List<Goods> goodsList=new ArrayList<>();goodsList.add(new Goods("18827382190","商品A"));goodsList.add(new Goods("83219078978","商品B"));goodsList.add(new Goods("83241781237","商品C"));goodsList.add(new Goods("18579831426","商品D"));System.out.println("排序前");System.out.println(goodsList);System.out.println("排序后");List<Goods> list=new CustomObjectSortSample().sort(goodsList);System.out.println(list);}
  }
  ​