Sorting a list with reference to a class without implementing in java

Question

So I get some names from user input and put them into a list that references class Person.

Class person has constructors with getters

public String getName(){
    return email;
}

But is also has setters with the exceptions so they can't insert a blank or improper name.

public void setFullName(String fullName) throws ValidationException{
    validateString(fullName);
    this.fullName = fullName;
}

But as it is based on user input, I have x amount of names. What I'm wanting to do is organize them alphabetically so that the first in the list won't necessarily be the first name I entered.

Here is the List and ArrayList that is in a constructor

private List<Person> peopleList;
public Contacts(){
    peopleList = new ArrayList<Person>();
}

I already know that I can't do

List<Person> subList = peopleList.subList(1, peopleList.size());
Collections.sort(subList);

Because I get "The method sort(List) in the type Collections is not applicable for the arguments (List)" from the Collections.sort

I can't implement a comparable or anything because it won't properly inherit an abstract method from class Person.

So how do I organize the list I have without implementation? If possible.

Please edit and summarize the main question and lead with with the main part of the question (e.g. put it in the beginning). The title isn't clear enough alone to show what you want to do. Then provide the minimum necessary code examples as background information and context. I had to read all of that stuff just to figure out whether or not I was in a position to answer the question. Your approach will turn off a lot of people who might be able to help you. — clearlight
– clearlight, Commented Mar 27, 2015 at 18:19

Jean-François Savard · Accepted Answer · 2015-03-27 18:21:20Z

1

Functional programming is your friend :

Collections.sort(peopleList, (Person p1, Person p2) -> p1.getFullName().compareTo(p2.getFullName()));

answered Mar 27, 2015 at 18:21

Jean-François Savard

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Comments

dkatzel · Accepted Answer · 2015-03-27 18:22:35Z

You don't have to modify the Person class to make it implement Comparable.

Instead you can write your own Comparator implementation which has the comparison method compare(a, b)

http://docs.oracle.com/javase/7/docs/api/java/util/Comparator.html

Collections.sort() has an overloaded version which takes the collection and comparator implementation to use.

public class NameCompartor implements Comparator<Person>{

@Override
public int compare(Person p1, Person p2) {
    // TODO Auto-generated method stub
    return p1.getFullName().compareTo(p2.getFullName());
}

}


Collections.sort(personList, new NNameCompartor());

Also, I'm not sure why you are taking a subList. Your sublist is skipping the first element (indexes are 0 based)

fonfonx · Accepted Answer · 2015-03-27 18:26:00Z

0

You can do something like that

class ComparatorPerson implements Comparator<Person>{
     public int compare(Person p1, Person p2){
            return p1.getFullName().compareTo(p2.getFullName());
     }
}

puis

 Collections.sort(subList, new ComparatorPerson());

answered Mar 27, 2015 at 18:26

fonfonx

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Comments

Stefaan Neyts · Accepted Answer · 2015-03-27 18:30:45Z

0

You should implement a custom comparator first

private Comparator<Person> alphabetical = new Comparator<Person>() {
    @Override
    public int compare(Person left, Person right) {
        return left.getName().compareTo(right.getName());
    }
}

Then you can use the Collections.sort() method with 2 arguments

Collections.sort(peopleList, alphabetical);

Or since Java 8 you can use a Lambda

Collections.sort(people list, (left, right) -> left.getName().compareTo(right.getName()));

answered Mar 27, 2015 at 18:30

Stefaan Neyts

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