[Edit]

Java - sort ArrayList based on Object field

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Created by:

TheDalot

390

In this article, we would like to show you how to sort ArrayList in a custom sorting order based on Object field in Java.

Quick solution:

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users.sort(new Comparator<User>() {
    public int compare(User u1, User u2) {
        if (u1.getAge() == u2.getAge())
            return 0;
        return u1.getAge() < u2.getAge() ? -1 : 1;
    }
});

Practical example

Edit

In this example, we create a custom Comparator that will help us to sort users ArrayList by users age.

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import java.util.*;
​
public class Example {
​
    public static void main(String[] args) {
        User user1 = new User(1, "Tom", 24);
        User user2 = new User(2, "Kate", 22);
        User user3 = new User(3, "Ann", 25);
​
        List<User> users = new ArrayList<>();
​
        users.add(user1);
        users.add(user2);
        users.add(user3);
​
        System.out.println("Before: " + users);
​
        users.sort(new Comparator<User>() {
            public int compare(User u1, User u2) {
                if (u1.getAge() == u2.getAge())
                    return 0;
                return u1.getAge() < u2.getAge() ? -1 : 1;
            }
        });
​
        System.out.println("After:  " + users);
    }
}

Output:

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Before: [User{ id=1, name='Tom', age=24 }, User{ id=2, name='Kate', age=22 }, User{ id=3, name='Ann', age=25 }]
After:  [User{ id=2, name='Kate', age=22 }, User{ id=1, name='Tom', age=24 }, User{ id=3, name='Ann', age=25 }]

Note:

We are able to print users in the Example class, because we have overridden toString() method in the User class.

User class:

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public class User {
    private final int id;
    private final String name;
    private final int age;
​
    public User(int id, String name, int age) {
        this.id = id;
        this.name = name;
        this.age = age;
    }
​
    public int getId() {
        return id;
    }
​
    public String getName() {
        return name;
    }
​
    public int getAge() {
        return age;
    }
​
    @Override
    public String toString() {
        return "User{ " +
                "id=" + id +
                ", name='" + name + '\'' +
                ", age=" + age +
                " }";
    }
}