java - alphabetical order (list)

Question

Possible Duplicate:
Sort List Alphabetically

how do i store my inputs in alphabetical order, i am inputting names into an arraylist:

    persons.add(person);

How to do that?

Just use Sort method of Collection where you pass the persons list. — , Dec 23 '10 at 13:13
Why don't you guys do your homework TOGETHER: http://stackoverflow.com/questions/1946668/sorting-using-comparator-descending-order-user-defined-classes. It's called a social activity :) — Lukas Eder, Dec 23 '10 at 13:20

score 9 · Answer 1 · answered Dec 23 '10 at 13:21

implements Comparator< T > interface

class A implements Comparator < Person > {

    @Override
    public int compare(Person o1, Person o2) {
        if(o1.getName() != null && o2.getName() != null){
            return o1.getName().compareTo(o2.getName());
        }

        return 0;
    }

}

then use Collections.sort(/* list here */, /* comparator here*/)

score 5 · Accepted Answer · edited Mar 24 '12 at 20:04

5

Try this:

 java.util.Collections.sort(people);

edited Mar 24 '12 at 20:04

Juan Manuel Serrat

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3

answered Dec 23 '10 at 13:09

Gerhard Presser

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Gondim · Answer 3 · 2010-12-23T14:30:26.283

5

Collection<Person> listPeople = new ArrayList<Person>();

The class Person.java will implements Comparable

public class Person implements Comparable<Person>{

public int compareTo(Person person) {
  if(this.name != null && person.name != null){
   return this.name.compareToIgnoreCase(person.name);
  }
  return 0;
 }

}

Once you have this, in the class you're adding people, when you're done adding, type:

Collections.sort(listPeople);

edited Dec 23 '10 at 14:30

answered Dec 23 '10 at 13:14

Gondim

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java.util.ArrayList() doesn't offer a sort() method! what programming language are you talking about? – Gerhard Presser Dec 23 '10 at 14:12
My bad, its Collections.sort(listPeople); – Gondim Dec 23 '10 at 14:30
Weird. I only get this error if I compile from the command line -- in Eclipse `ArrayList` totally has a `.sort` method. Maybe it's a version issue? – BrainSlugs83 May 11 '15 at 03:07
In Java 7, ArrayList does not have sort method. In Java 8, it has. – Dayong Jun 11 '15 at 15:26

score 0 · Answer 4 · answered Dec 23 '10 at 13:08

0

use TreeSet instead of ArrayList

answered Dec 23 '10 at 13:08

Vladimir Ivanov

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No, the thing is that i have to use ArrayList because i have to learn it. – Jake Dec 23 '10 at 13:09
3

That's not really a very good answer. TreeSet is a set, not a list. If he follows blindly this answer, he could go into problems (notably, no more duplicate elements) without knowing why. – Valentin Rocher Dec 23 '10 at 13:19
The question was how to store the elements in alphabetical order, no restrictions on the collection in the question. The fact that he is using array list doesn't mean anything. – Vladimir Ivanov Dec 23 '10 at 13:22

java - alphabetical order (list)

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