How do I sort an ArrayList of strings by alphabetical order?

Question

I'm trying to create a program that can sort the contents of an ArrayList alphabetically. Right now I have three classes in my program...

Dog

public class Dog {
    private String name;

    public Dog(){

    }

    public void setName(String name){
        this.name = name;
    }

    public String getName(){
        return this.name;
    }
}

DogList (which contains the ArrayList of type Dog)

import java.util.ArrayList;

public class DogList {

    private ArrayList<Dog> dogList;

    public DogList(){
        DogList = new ArrayList<>();
    }

    public void setSize(int DogSize){
        for(int x = 0; x <= DogSize; x++){
            DogList.add(new Dog());
        }
    }

    public ArrayList<Dog> getList(){
        return dogList;
    }
}

and the last class, DogSorter, which is trying to access DogList ArrayList and then trying to sort the contents of that ArrayList in alphabetical order.

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;


public class DogSorter {
    private DogList list = new DogList();

    public void sortDogs{
        Collections.sort(list);
    }

    for(i = 0; i < list.length(); i++) {
        System.out.println(list.getList().get(i).getName();
    }
}

I apologize for the long post. My question is simply: How do I sort the contents of the ArrayList accurately? I keep getting an error saying that I'm trying to compare the wrong types with my "Collections.sort" line. If anyone can help out, please let me know. Thank you.

edit: To be clear, I'm trying to sort them alphabetically by the string stored in getName() for each object

Btw: why do you post code which is obviously not the code you're working with? Please avoid that. — Tom, Dec 06 '15 at 10:07

Nayanjyoti Deka · Answer 1 · 2018-09-23T19:19:32.023

8

Use

Collections.sort(dogList, new Comparator<Dog>(){
    public int compare(Dog d1, Dog d2){
         return d1.getName().compareTo(d2.getName());
    }    
});

This will compare each dogs based on comparator. Comparator simply compares the names of dogs.

Update: For idiomatic java 8 style

Collections.sort(dogList, (d1,d2) -> d1.getName().compareTo(d2.getName()));

edited Sep 23 '18 at 19:19

answered Dec 06 '15 at 10:00

Nayanjyoti Deka

419
3
15

score 7 · Accepted Answer · answered Dec 06 '15 at 09:58

kindly follow this way, don't make code too much stuff, here i see you have mess up you code and it makes difficult to understand easily.

kindly follow this easiest way to sort Dog Object's list in sorting order(Ascending/Descending) way.

import java.util.ArrayList;
import java.util.Collections;


class Dog implements Comparable<Dog>{
    String name;

    Dog(String name){
        this.name = name;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Override
    public int compareTo(Dog o) {
        return this.name.compareTo(o.getName()); // dog name sort in ascending order 
        //return o.getName().compareTo(this.name); use this line for dog name sort in descending order 
    }

    @Override
    public String toString() {
        return this.name;
    }
}


public class DogSort {

    public static void main(String[] args) {
        ArrayList<Dog> listDog = new ArrayList<Dog>();
        listDog.add(new Dog("doggy"));
        listDog.add(new Dog("aaa"));
        listDog.add(new Dog("bbb"));
        System.out.println(listDog);
        Collections.sort(listDog);
        System.out.println(listDog);

    }

}

score 4 · Answer 3 · answered Dec 06 '15 at 10:01

4

You can sort it with:

  Collections.sort(list);

answered Dec 06 '15 at 10:01

Abdelhak

8,299
4
22
36

2

Not helpful for OP, because he already does that ... – Tom Dec 06 '15 at 10:02

score 2 · Answer 4 · answered Dec 06 '15 at 09:51

2

You'll need to implement the Comparator interface.

answered Dec 06 '15 at 09:51

ifly6

5,003
2
24
47

guillaume girod-vitouchkina · Answer 5 · 2015-12-06T09:57:10.200

2

You use the same name DogList, for your class and the variable. Change it.

For example:

private ArrayList<Dog> innerList;

in your DogList class, declare a sort method

public sort() { 
Collections.sort(innerList);
}

and your Dog class must be comparable

public class Dog implements Comparable {

public int compareTo(Object _other)
{
// DO the comparaison
return 1;
}

}

edited Dec 06 '15 at 09:57

answered Dec 06 '15 at 09:51

guillaume girod-vitouchkina

3,061
1
10
26

You're using a raw types, because...? – Tom Dec 06 '15 at 10:03

score 2 · Answer 6 · edited May 23 '17 at 12:34

2

You can use Comparator to solve this ..

I hope this will solve your issue - How to sort an ArrayList in Java

edited May 23 '17 at 12:34

Community

1
1

answered Dec 06 '15 at 09:53

Ali

427
1
4
14

And how should your advice work? Neither is `list` an array nor does it contain one. – Tom Dec 06 '15 at 10:10

score 1 · Answer 7 · answered Dec 06 '15 at 10:13

1

Either implement the Comparable interface in your Dog class or write a custom Comparator which would sort Dog on their name.

answered Dec 06 '15 at 10:13

Amit

383
3
15

How do I sort an ArrayList of strings by alphabetical order?

7 Answers7