How to sort elements in an ArrayList of Strings?

Question

 PhoneBookCollection phoneBook = new PhoneBookCollection();

I have an ArrayList of PhoneBook objects. (The getCollection method returns the list)

ArrayList<PhoneBook> list = phoneBook.getCollection();

I then iterate through my ArrayList and get the PhoneBook at the i'th index and get its corresponding Telephone.

for(int i = 0; i < list.size(); i++ ){

String phone = phoneBook.getPhoneBook(i).getTelephone();

}

What I want to be able to do now is sort the getTelephone objects in ascending order. I know that ArrayLists don't have a sort method so i'm having a bit of trouble doing this.

1) For better help sooner, post an SSCCE. 2) Please don't forget to add a '?' to questions! Some people do a search in the page for '?' and if none exists in the 'question' go directly to the next (actual) question in line. — Andrew Thompson
– Andrew Thompson, Commented Dec 15, 2013 at 18:24
Assuming your PhoneBooks aren't comparing by Telephone Number, you could write a PhoneBookComparator and use Collections.sort(). — Elliott Frisch
– Elliott Frisch, Commented Dec 15, 2013 at 18:32

Christian Tapia · Accepted Answer · 2013-12-15 18:32:45Z

2

You can create a class that implements Comparator:

public class CustomComparator implements Comparator<PhoneBook> { // Replace PhoneBook with the appropriate
    @Override
    public int compare(PhoneBook t1, PhoneBook t2) {
        return t1.getNumber().compareTo(t2.getNumber()); // Here compare the telephone numbers
    }
}

Then do this:

Collections.sort(list, new CustomComparator());

answered Dec 15, 2013 at 18:32

Christian Tapia

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5 Comments

Ryman Holmes Over a year ago

I understand the part where you are comparing the 2 Telephone numbers but where would I do do Collections.sort(list, new CustomComparator());?

Christian Tapia Over a year ago

It depends in when and where you want to sort your ArrayList.

Ryman Holmes Over a year ago

I only want to sort the Phone Numbers not the whole ArrayList as a PhoneBook object stores other attributes such as name, address etc...

Christian Tapia Over a year ago

So you want another ArrayList with just the telephones sorted?

Ryman Holmes Over a year ago

Looks like another collection is the only way to sort the telephones only... but I'm going to have to loop again and that increases time complexity

pulasthi7 · Accepted Answer · 2013-12-15 18:30:43Z

0

You can use the java.util.Collections class to sort the lists. Use Collections.sort().

answered Dec 15, 2013 at 18:30

pulasthi7

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Udi Cohen · Accepted Answer · 2013-12-15 18:31:07Z

0

You can use the java.util.Collections for that.

answered Dec 15, 2013 at 18:31

Udi Cohen

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catch32 · Accepted Answer · 2013-12-15 18:32:54Z

0

The best will be use standart way with java.util.Collections

String class has method compareTo() and will be sorted automtically:

Collections.sort(nameOfList)

answered Dec 15, 2013 at 18:32

catch32

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