sort List of bean object in java alphabetically in ascending order

Question

Below is the bean class:

public class bean  {
    private String Name;

    public String getName() {
        return Name;
    }

    public void setName(String name) {
        Name = name;
    }



    @Override
    public String toString() {
        return "bean [Name=" + Name + "]";
    }
}

Below is my java class where i am trying to sort the list of beans in ascending order(i mean alphabetical order):

 public class Test{
    public static void main(String[] args) {
        bean b1 = new bean();
        bean b2 = new bean();
        bean b3 = new bean();
        List<bean> beanList = new ArrayList<bean>();
        b1.setName("b");
        b2.setName("a");
        b3.setName("Z");
        beanList.add(b1);
        beanList.add(b2);
        beanList.add(b3);

    }
}

i am unable to achieve the sorting of the bean value in alphabetical order like a,b,z. can anyone please suggest

was trying to find the various ways where i can achieve. at the end the functionality was to achieve the alphabetical ordering, in which i was failing — Sangeetha cg, Apr 04 '16 at 16:52
Look your implementation of compareTo(): it always returns 0. So all the objects are considered equal by your comaprison method. And please, respect the Java naming conventions: classes start with an uppercase letter, so bean -> Bean. Variables start with a lowercase letter, so Name -> name. — JB Nizet, Apr 04 '16 at 16:57
yeah sure will follow. public int compareTo(bean b1, bean b2) { return b1.getName().compareTo(b2.getName()); } i have added this code still it does not work — Sangeetha cg, Apr 04 '16 at 17:00
This is not the method that implement Comparable. You should remove it: it's useless. Read the javadoc of Comparable. Does it have a method with two arguments? — JB Nizet, Apr 04 '16 at 17:12

score 3 · Accepted Answer · edited Jun 20 '20 at 09:12

3

You are sorting 2 times and that is more that what you need

1st Test doesnt need to implement comparable...

public class Test  {
    public static void main(String[] args) { 
        Bean b1 = new Bean();
        Bean b2 = new Bean();
        Bean b3 = new Bean();
        List<Bean> beanList = new ArrayList<Bean>();
        b1.setName("b");
        b2.setName("a");
        b3.setName("Z");
        beanList.add(b1);
        beanList.add(b2);
        beanList.add(b3);
        
        Collections.sort(beanList);
        System.out.println("finally " + beanList);
    }
}

and the bean class should compare the strings since that is the sort criteria

public class Bean implements Comparable<Bean> {
    private String Name;

    public String getName() {
        return Name;
    }

    public void setName(String name) {
        Name = name;
    }

    @Override
    public String toString() {
        return "bean [Name=" + Name + "]";
    }

    @Override
    public int compareTo(Bean o) {
        return o.getName().compareTo(this.getName());
    }
}

edit:

you can for sure add more than one field to the bean class, example: lastname or you can use an anonymous comparator and sort with yoor own criteria

Example with last name:

public class Bean implements Comparable<Bean> {
    private String name;
    private String lastName;

    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    public String getName() {
        return name;
    }

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

    @Override
    public String toString() {
        return "Bean [name=" + name + ", lastName=" + lastName + "]";
    }
 
    @Override
    public int compareTo(Bean o) {
        return this.getName().compareTo(o.getName());
    }
}

edited Jun 20 '20 at 09:12

Community

1
1

answered Apr 04 '16 at 17:08

ΦXocę 웃 Пepeúpa ツ

47,427
17
69
97

Thank you for valuable suggestion – Sangeetha cg Apr 04 '16 at 17:13
i just have one query , i have the name as well as the last name so overall i display fullname in jsp page that includes name+lastname. so sorting name only will not work right?so should i need to sort the lastname as well? public int compareTo(Bean o) { return o.getName().compareTo(this.getName()); } public int compareTo(Bean o) { return o.getlName().compareTo(this.getlName()); } – Sangeetha cg Apr 04 '16 at 17:29
i did not get you could you please explain with example in brief – Sangeetha cg Apr 04 '16 at 17:34
hey... I have a question, do you want to sort by last name or name? – ΦXocę 웃 Пepeúpa ツ Apr 04 '16 at 17:43
both say for eg: i get Name = zarine Lname = Satiago , Name=Rocky Lname=Mad. the list contains fullname(zarine Satiago,Rocky Mad ) after sorting i need to get it as fullname = Rocky Mad ,zarine Satiago – Sangeetha cg Apr 04 '16 at 17:49
seems like sorting name attribute only is sufficient will also sort the lname and fetch its corresponds value – Sangeetha cg Apr 04 '16 at 17:58
Answer updated, take a look, try it and let me know – ΦXocę 웃 Пepeúpa ツ Apr 04 '16 at 18:02
hey thanks , that means sorting name is sufficient i guess, it will pick up its corresponding lname as well right – Sangeetha cg Apr 04 '16 at 18:04

Sendhilkumar Alalasundaram · Answer 2 · 2016-04-04T17:33:35.823

2

The first implementation of sort which uses the inline definition of comparator is correct.

You would find that in the the sorted beans occur in the order of "Z","a" and "b".

Capital Z is being compared with small letters a and b. Hence, the sorted list is in above order

If you wish that the comparison should be case insensitive, you can use tolowercase on both strings before comparison.

Refer foll. code snippet:

Collections.sort(beanList, new Comparator<bean>() {
                public int compare(final bean object1, final bean object2) {
                    return object1.getName().toLowerCase().compareTo(object2.getName().toLowerCase());
                }
            });

You can also use compareToIgnoreCase() method as follows:

Collections.sort(beanList, new Comparator<bean>() {
                public int compare(final bean object1, final bean object2) {
                    return object1.getName().compareToIgnoreCase(object2.getName());
                }
            });

Alternatively, you can use the second method(Collections.sort()), where you do not mention explicitly the comparator, while invoking sort on the Collection. This would be possible as the bean class implements the comparable interface.

For implementing the comparable interface, compareTo method would have to implemented as follows:

@Override
public int compareTo(bean o) {
    return this.Name.compareToIgnoreCase(o.Name);
}

edited Apr 04 '16 at 17:33

answered Apr 04 '16 at 17:07

Sendhilkumar Alalasundaram

1,733
14
24

Thank you for your suggestion. you are right. – Sangeetha cg Apr 04 '16 at 17:12
what if i want to sort more than one parameter like lastname as well ? should i use another compareTo? also can you please tell me where can i use your collections.sort in Bean class or in Test class? – Sangeetha cg Apr 04 '16 at 17:43
In java8, Comparator that compares name and lastname can be implemented by doing: Comparator c = Comparator.compare(bean::getName).andThen(bean::getLastName); – Sendhilkumar Alalasundaram Apr 04 '16 at 17:52
A little note: if my answer worked for you, please mark it as right. – Sendhilkumar Alalasundaram Apr 04 '16 at 17:53
yeah sure, i am using java 7 is there anyother alterative? – Sangeetha cg Apr 04 '16 at 18:00
http://stackoverflow.com/questions/369512/how-to-compare-objects-by-multiple-fields The second answer is what you want. – Sendhilkumar Alalasundaram Apr 04 '16 at 18:02
Thank you very ,much , i wanted mark it as right , but my reputations are less i am unable to mark it as right sorry :( – Sangeetha cg Apr 04 '16 at 18:09
You don't need reputation to mark answer as right. And I can see you have enough reputation to upvote an answer, so marking right will not be a problem. – Sendhilkumar Alalasundaram Apr 05 '16 at 02:11
yes now i am able to upvote. thanks – Sangeetha cg Apr 05 '16 at 03:47

sort List of bean object in java alphabetically in ascending order

2 Answers2

edit:

Example with last name: