我该如何更改我的数组列表？

Question

i search more about my problem, but know i thought about it and i need to alter the arraylist. I saw about this fuctions Collections.swap(list,x,y), and this is cool, but only if i like to change one element for other. So i need a method that change the first places and put my users online with this condition:

if(userpresence.getmode()==null&&userpresence.isAvailable()){
listItem.add(new contacts(name,user,icon))
}
if(userpresence.getmode()==null&&!userpresence.isAvailable()){
    listItem.add(new contacts(name,user,icon))
}

in this part i show the list sort aphabetically:

    Collections.sort(listItem);

//I think the method about I tell you is in this part 

    ObservableList<Contacts> ob=FXCollections.observableArrayList(listItem);
    listview.setitems(ob);

and the idea is something like this:

user online
user online
user online
user online
user offline
user offline
user offline
user offline
user offline

but in this case only i show in this way:

user offline
user offline
user offline
user offline
user offline
user online
user offline
user offline
user offline
user online
user offline
user offline
user offline
user online
user offline
user offline
user offline
user online
user offline
user offline
user offline
user online
user offline
user offline
user offline
user offline
user online
user offline
user offline

because I try to do the comparasing and the effect about this not shown. this is my method comparator:

public static Comparator<Contacts> contactsComparator=new Comparator<Contacts>(){
    @Override
    public int compare(Contacts c1, Contacts c2) {
        String ContactName1=c1.getName().toUpperCase();
        String ContactName2=c2.getName().toUpperCase();


        return ContactName1.compareTo(ContactName2);
    }
};

and in the collections.sort i put this (arraylist,contacts.contactsComparator)

Answer 1

Collections.sort(list) only works if your objects implement the interface java.lang.Comparable . Otherwise you need to implement and pass a java.util.Comparator to the sort method as well. Either is needed to define the sort order for your objects.