How to use a Java8 lambda to sort a stream in reverse order?

Question

I\'m using java lambda to sort a list.

how can I sort it in a reverse way?

I saw this post, but I want to use java 8 lambda.

Here is my code (I used

Answer 1

If you want to sort by Object's date type property then

public class Visit implements Serializable, Comparable<Visit>{
private static final long serialVersionUID = 4976278839883192037L;

private Date dos;

public Date getDos() {
    return dos;
}

public void setDos(Date dos) {
    this.dos = dos;
}

@Override
public int compareTo(Visit visit) {
    return this.getDos().compareTo(visit.getDos());
}

}

List<Visit> visits = getResults();//Method making the list
Collections.sort(visits, Collections.reverseOrder());//Reverser order

Answer 2

You can use a method reference:

import static java.util.Comparator.*;
import static java.util.stream.Collectors.*;

Arrays.asList(files).stream()
    .filter(file -> isNameLikeBaseLine(file, baseLineFile.getName()))
    .sorted(comparing(File::lastModified).reversed())
    .skip(numOfNewestToLeave)
    .forEach(item -> item.delete());

In alternative of method reference you can use a lambda expression, so the argument of comparing become:

.sorted(comparing(file -> file.lastModified()).reversed());

Answer 3

In simple, using Comparator and Collection you can sort like below in reversal order using JAVA 8

import java.util.Comparator;;
import java.util.stream.Collectors;

Arrays.asList(files).stream()
    .sorted(Comparator.comparing(File::getLastModified).reversed())
    .collect(Collectors.toList());

Answer 4

Use

Comparator<File> comparator = Comparator.comparing(File::lastModified); 
Collections.sort(list, comparator.reversed());

Then

.forEach(item -> item.delete());

Answer 5

You can define your Comparator with your own logic like this;

private static final Comparator<UserResource> sortByLastLogin = (c1, c2) -> {
    if (Objects.isNull(c1.getLastLoggedin())) {
        return -1;
    } else if (Objects.isNull(c2.getLastLoggedin())) {
        return 1;
    }
    return c1.getLastLoggedin().compareTo(c2.getLastLoggedin());
};   

And use it inside foreach as:

list.stream()
     .sorted(sortCredentialsByLastLogin.reversed())
     .collect(Collectors.toList());

Answer 6

For reverse sorting just change the order of x1, x2 for calling the x1.compareTo(x2) method the result will be reverse to one another

Default order

List<String> sortedByName = citiesName.stream().sorted((s1,s2)->s1.compareTo(s2)).collect(Collectors.toList());
System.out.println("Sorted by Name : "+ sortedByName);

Reverse Order

List<String> reverseSortedByName = citiesName.stream().sorted((s1,s2)->s2.compareTo(s1)).collect(Collectors.toList());
System.out.println("Reverse Sorted by Name : "+ reverseSortedByName );