How to sort LocalDateTime and get Max and min?

Question

Can anyone share the logic to sort the LocalDateTime and get max and min record from list of domain object.

Domain Object-

private int employeeNumber;
private LocalDateTime updatedDate;

First Record

1.1,2016-07-09 00:00:00+0000
2.2,2017-10-06 23:25:37+0000

Max Output: 2,2017-10-06 23:25:37+0000

Min Output: 1,2016-07-09 00:00:00+0000

Solution 1

Assume that your Domain Object name as "Employee" and have List<Employee> as the list of Domain Objects. Then, you may use Java 8 sort function by passing a Comparator as follows. Subsequently, you shall extract Min and Max as you wish.

employeeList.sort((Employee e1, Employee e2) -> e1.getUpdatedDate().compareTo(e2.getUpdatedDate()));

Find the below code sample for your reference.

import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;
import java.util.Arrays;
import java.util.List;

public class Main {
    static DateTimeFormatter format = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ssxx");

    static Employee emp1 = new Employee(1, LocalDateTime.parse("2017-10-06 23:25:37+0000", format));
    static Employee emp2 = new Employee(2, LocalDateTime.parse("2016-07-09 00:00:00+0000", format));
    static Employee emp3 = new Employee(3, LocalDateTime.parse("2017-10-06 23:25:38+0000", format));
    static Employee emp4 = new Employee(4, LocalDateTime.parse("2016-07-09 00:00:00+0000", format));

    static List<Employee> employeeList = Arrays.asList(new Employee[] { emp1, emp2, emp3, emp4 });

    public static void main(String[] args) {
        employeeList.sort((Employee e1, Employee e2) -> e1.getUpdatedDate().compareTo(e2.getUpdatedDate()));

        System.out.println("Max:" + employeeList.get(employeeList.size() - 1));
        System.out.println("Min:" + employeeList.get(0));

        System.out.println("==== Complete list ===");
        employeeList.forEach(e -> System.out.println(e));

    }
}

class Employee {
    private int employeeNumber;
    private LocalDateTime updatedDate;

    public Employee() {
    }

    public Employee(int employeeNumber, LocalDateTime updatedDate) {
        this.employeeNumber = employeeNumber;
        this.updatedDate = updatedDate;
    }

    public int getEmployeeNumber() {
        return employeeNumber;
    }

    public void setEmployeeNumber(int employeeNumber) {
        this.employeeNumber = employeeNumber;
    }

    public LocalDateTime getUpdatedDate() {
        return updatedDate;
    }

    public void setUpdatedDate(LocalDateTime updatedDate) {
        this.updatedDate = updatedDate;
    }

    public String toString() {
        return String.format("Employee Number: %s, Updated Date: %s", this.employeeNumber, this.updatedDate);
    }
}

Solution 2

Your simplified dataset

DateTimeFormatter fmt = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ssxx");
dates.add(LocalDateTime.parse("2016-07-09 00:00:00+0000", fmt));
dates.add(LocalDateTime.parse("2017-10-06 23:25:37+0000", fmt));

Converting the hashset to streams and producing min and max out of it

System.out.println("Min: " + dates.stream().min(LocalDateTime::compareTo));
System.out.println("Max: " + dates.stream().max(LocalDateTime::compareTo));

Output:

Min: 2016-07-09T00:00
Max: 2017-10-06T23:25:37

You can easily adapt this core logic to your scenario now.

Comments

[Parag Kadam]

How can I use the above code if in place of dates there are employees which has a property lastSeen which is java.sql.Timestamp and I want to get an employee with the highest lastSeen?