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.

Answer 1

函数式编程是您的朋友：

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

Answer 2

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)

Answer 3

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());

Answer 4

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()));