Java：排序第一个元素具有链表的数组列表

Question

Consider this arraylist with linkedlist objects (are->1->3->7 , croco-> 4 ->1 , bat ->3->8).
Now I have to sort the arraylist in java in ascending order considering the first element of linkedlist contained in arraylist. There is a method Collections.sort() but it is useful when objects are strings. What to apply in this situation? The final list should look something like this (are->1->3->7 , bat ->3->8 , croco-> 4 ->1 )

Answer 1

Collections.sort(); has an overloaded method that takes a comparator as well. So you want something like this:

Collections.sort(lists, (o1, o2) ->
        o1.get(0).compareTo(o2.get(0))
);

Or if you can use Java 8, there is a default sort method in List interface:

lists.sort(Comparator.comparing(o -> o.get(0)));

Answer 2

Without much context, I might be wrong. However, from my judgement if you're using your own objects which contain an identifier (are, croco and bat), and a linkedlist(numbers), then you can use the following solution.

Your class needs to implement the Comparable Interface You need to override the compareTo() method Collections.sort() should sort your objects in ascending order.

public class Example implements Comparable {
    private String identifier;
    private List<Integer> list;

    // constructors
    // getters

    @Override
    public int compareTo(Object other){ 
    if(this.list.head() > other.list.head()) return 1; 
    if(this.list.head() < other.list.head()) return -1;
    else return 0;
    }
}