How can I sort an ArrayList of objects?

Question

I have and ArrayList with two strings and an Integer, but I just need to sort it by the string Name and the string LastName, I tried with the method Collections.sort like this

 Collections.sort(MyArrayList, (Contact v1, Contact v2) -> v1.getName().compareTo(v2.getname()));

But this sorts my ArrayList just by the names, and doesn't include the last name, how can I add to the sort the last names?

• Lyubomyr Shaydariv: Possible duplicate: stackoverflow.com/questions/1421322/… . Your comparator must respect the last name too.

Answer 1

Use Comparator.comparing(Contact::getName).thenComparing(Contact::getLastName) for your Comparator:

Collections.sort(MyArrayList, Comparator.comparing(Contact::getName).thenComparing(Contact::getLastName));

Answer 2

Well you just need to change your comparison function to include other fields like this

 Collections.sort(contacts, (Contact c1, Contact c2) -> {
 int firstNameComparisonResult = c1.getFirstName().compareTo(c2.getFirstName());
 if (firstNameComparisonResult != 0) {
 return firstNameComparisonResult;
 } else {
 return c1.getLastName().compareTo(c2.getLastName());
 }
 });

Warning: this assumes there are no nulls.

Full code I used if you want to take a look:

class Contact{
 final String firstName;
 final String lastName;
 final int age;
 public String getFirstName() {
 return firstName;
 }
 public String getLastName() {
 return lastName;
 }
 public int getAge() {
 return age;
 }
 public Contact(String firstName, String lastName, int age) {
 this.firstName = firstName;
 this.lastName = lastName;
 this.age = age;
 }
 @Override
 public String toString() {
 return "Contact{" +
 "firstName='" + firstName + '\'' +
 ", lastName='" + lastName + '\'' +
 ", age=" + age +
 '}';
 }
}
@Test
public void sortTest(){
 List<Contact> contacts = new ArrayList<>();
 contacts.add(new Contact("A","B",37));
 contacts.add(new Contact("A","C",34));
 contacts.add(new Contact("B","A",35));
 Collections.sort(contacts, (Contact c1, Contact c2) -> {
 int firstNameComparisonResult = c1.getFirstName().compareTo(c2.getFirstName());
 if (firstNameComparisonResult != 0) {
 return firstNameComparisonResult;
 } else {
 return c1.getLastName().compareTo(c2.getLastName());
 }
 });
 System.out.println(contacts);
 //[Contact{firstName='A', lastName='B', age=37}, Contact{firstName='A', lastName='C', age=34}, Contact{firstName='B', lastName='A', age=35}]
}

Answer 3

Well ... transform your closure into a full anonymous class, and use that power to increase your sort complexity ...

Something like

 Collections.sort(MyArrayList, new Comparator<Contact>() {
 public int compare(Contact v1, Contact v2) {
 int returned = v1.getvName().compareTo(v2.getname())
 if(returned==0) {
 // alas, Math.signum returns a float value in this cas
 returned = (int) Math.signum(v1.getYourInt(), v2.getYourInt())
 }
 return returned;
 }
 });

WARNING This code has not been compiled in any way.