JAVA: How to sort list on the base of the field

Question

I have the following list and I want to sort this whole list on the basis of the date how can I do this?

List<DevicePing> devicePing=Arrays.asList(
                new DevicePing(1L,2017-11-21 10:10:10.0),
                new DevicePing(2L,2017-11-21 10:00:00.0),
                new DevicePing(3L,2017-11-21 10:15:10.0),
                new DevicePing(4L,2017-11-21 09:30:10.0),
                new DevicePing(5L,2017-11-21 09:45:10.0),
                new DevicePing(6L,2017-11-21 09:50:10.0),
                new DevicePing(7L,2017-11-21 09:55:10.0);

When I am using the following code it gives me an nullPointerException at o1.getDateTime()

Collections.sort(myList, new Comparator<MyObject>() {
  public int compare(MyObject o1, MyObject o2) {
      return o1.getDateTime().compareTo(o2.getDateTime());
  }
});

EDITED

Now I am using the following code but it print the same data instaed of sorted data

public void calculateTimesheet(RiderLocation riderLocation,List<DevicePing> devicePing,List<RiderAvailability> riderAvailability)
    {
        devicePing.sort(Comparator.comparing(DevicePing::getDate));
        for(DevicePing dp:devicePing)
        {
            System.out.println("dp: " + dp);
        }
    }

DevicePing.java

@Entity
public class DevicePing {

    public DevicePing(Long id ,Date createdAt) {
        this.id = id;
        this.createdAt = createdAt;
    }

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @ManyToOne
    private User rider;

    @Column( nullable = false,columnDefinition = "TIMESTAMP DEFAULT CURRENT_TIMESTAMP")
    @Temporal(TemporalType.TIMESTAMP)
    private Date date;

    //getter nad setter
    }

Use a Comparator - https://stackoverflow.com/questions/2839137/how-to-use-comparator-in-java-to-sort — MikeJ, Nov 21 '17 at 11:42
Also you're not showing the complete code. Please read upon [mcve] — jontro, Nov 21 '17 at 11:42
As an aside, in particular since you can use Java 8, I suggest you skip the long outdated `Date` class and instead use a class from `java.time`, the modern Java date and time API, for example `Instant` or `LocalDateTime` (the choice depending on your more exact requirements). — Ole V.V., Nov 21 '17 at 12:24
For your `NullPointerException`, could your list contain a `null`? — Ole V.V., Nov 21 '17 at 12:26

score 3 · Accepted Answer · answered Nov 21 '17 at 11:42

3

Try sorting it using:

devicePing.sort(Comparator.comparing(DevicePing::getDateTime));

answered Nov 21 '17 at 11:42

syncdk

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`public void calculateTimesheet(RiderLocation riderLocation,List devicePing,List riderAvailability) { devicePing.sort(Comparator.comparing(DevicePing::getDate)); for(DevicePing dp:devicePing) { System.out.println("dp: " + dp); } }` I am tried your example but it prints the same data not sorted data – SFAH Nov 21 '17 at 11:47
`DevicePing::getDateTime`, All your dates are on the same day. Use the Date and time – syncdk Nov 21 '17 at 11:51
Actually it is a time stamp please check my edited question – SFAH Nov 21 '17 at 11:54
What is the Java type? `LocalDateTime`? `Date`? – syncdk Nov 21 '17 at 11:55
And I want to sort my list on the basis of the timestamp – SFAH Nov 21 '17 at 11:56
Java type is Date – SFAH Nov 21 '17 at 11:56
It works fine now.. Sorry it was my mistake , Thankyou so much God bless you – SFAH Nov 21 '17 at 11:59
No problem, glad I could help :) – syncdk Nov 21 '17 at 12:00

JAVA: How to sort list on the base of the field

1 Answers1