CODEWITHSUNDEEP
javadatecomparator
akram
akram

Reputation: 517

Compare Object by dates ( implements Comparator)

I have a java People object :

public class People {

        String lastname;
        String firstname;
        String gender;
        String datebirth;
        String fcolor;

        public People(String lastname, String firstname, String gender,String datebirth, String fcolor) {
                this.lastname = lastname;
                this.firstname = firstname; 
                this.gender = gender;
                this.datebirth = datebirth;
                this.fcolor = fcolor;
        }
        public String getLastname() {
                return lastname;
        }
        public String getFirstname() {
                return firstname;
        }
        public String getGender() {
                return gender;
        }
        public String getFcolor() {
                return fcolor;
        }
        public String getDatebirth() {
                return datebirth;
        }        
}

I want to create a Comparator to compare by datebirth (datebirth is sometimes in this format "2/13/1943", sometimes in this format "2-13-1943", can you help me on how to implement it.

I started this , but got confused :

import java.util.Date;
import java.text.SimpleDateFormat;
import java.util.Comparator;
import java.text.DateFormat;

public class CompareDateBirth implements Comparator<People>{

        public int compare(People p, People q) {

                 DateFormat df = new SimpleDateFormat("dd-MM-yyyy");
                 Date Pdate = null;
                 Date Qdate= null;
                    try {
                    Pdate = df.parse(p.getDatebirth());
                    Qdate = df.parse(q.getDatebirth());
                    } catch (Exception e) {
                    e.printStackTrace();
                    }    
                      return Pdate.compareTo(Qdate) > 0 ? 1 : 0;
        }
}

Upvotes: 4

Views: 43207

Answers (4)

Fede Garcia
Fede Garcia

Reputation: 787

You can use lambdas and out-of-the-box comparators since java 8, like this:

java.util.Comparator.comparing(Person::getBirthDate)

Upvotes: 1

duffymo
duffymo

Reputation: 308743

If you'd store birth date using its proper type - a java.util.Date object instead of a String - you wouldn't have this problem. Formatting is a display issue.

A class named "People"?

Here's how I might do it (all classes below in separate .java files in a package named model):

package model;

public enum Gender { MALE, FEMALE }

public class Person {
    private String firstName;
    private String lastName;
    private Gender gender;
    private Date birthDate;  // I'd make sure to set hh:mm:ss all to midnight

    // constructors, getters, equals, hashCode, and toString are left for you
}

public class BirthDateComparator implements Comparator<Person> {
    public int compare(Person p, Person q) {
        if (p.getBirthDate().before(q.getBirthDate()) {
            return -1;
        } else if (p.getBirthDate().after(q.getBirthDate()) {
            return 1;
        } else {
            return 0;
        }        
    }
}

Upvotes: 13

CA_Eagle
CA_Eagle

Reputation: 21

Public class BirthDateComparator implements java.util.Comparator<Person> {
   public int compare(Person p1, Person p2) {
        return p1.getBirthDate().compareTo(p2.getBirthDate());
   }
}

Upvotes: 1

Ajibola
Ajibola

Reputation: 1238

I suggest saving the date in your java code as a long that has the UNIX time of that date, it is more dependable across platforms. Also you could manually split the date using a delimiter, so if there is a '-' then that is your delimiter, else if there exists '/' then you split using that instead.

That way you can extract the day, month and year and construct the date object.

Upvotes: 1

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