JAVA sorts the list set Collections.sort of

Sort the objects in a collection in ascending or descending order according to the size of a certain index of the object. The code is as follows:

So let's do it in descending order

  So let's do it in descending order 
    Collections.sort(list, new Comparator<ResultTypeDesc>() {
      public int compare(ResultTypeDesc o1, ResultTypeDesc o2) {
        return o2.getRatio().compareTo(o1.getRatio());
      }
    });

I'm going to do it in ascending order

Collections.sort(list, new Comparator<ResultTypeDesc>() {
public int compare(ResultTypeDesc o1, ResultTypeDesc o2) {
return o1.getRatio().compareTo(o2.getRatio());
   }
});

After testing, it is found that only need to change the position of the two objects 1 can be ascending or descending.

If the indexes are the same, sort them according to multiple indexes, and create a comparator:

import java.util.*;

public class ComparatorResultType implements Comparator{

 public int compare(Object arg0, Object arg1) {
 ResultTypeDesc desc0=(ResultTypeDesc)arg0;
 ResultTypeDesc desc1=(ResultTypeDesc)arg1;

  // First compare the main index, if the main index is the same, then compare the secondary index 

 int flag=desc0.getXXX().compareTo(desc1.getXXX());
 if(flag==0){
  return desc0.getXXX2().compareTo(desc1.getXXX2());
 }else{
  return flag;
 } 
 }
}

// Code in the test class: 
ComparatorResultType comparator=new ComparatorResultType();
Collections.sort(list, comparator);

Inverse output of list set:

Collections.reverse(list);

ResultTypeDesc is the required entity class object, which can be used in combination with its own code.

It is possible for this method to declare a null pointer, solve it by itself in combination with the situation, and judge whether it is NULL.