Here is my problem, I have a LinkedList of objects, which have a String name and an int score value.
Now, I need to sort this list in descending order based on the score value.
How do I do that? I tried with Collections.sort(List), but that doesn't work with objects.
How do I tell Java to use the score as the value to comparison?
The Collections.sort method accepts a comparator as its second argument.
You can pass in a comparator that defines the ordering that you want.
For example given a Person class:
class Person {
private final String name;
private final int score;
Person(String name, int score) {
this.name = name;
this.score = score;
}
@Override
public String toString() {
return "Person{" +
"name='" + name + '\'' +
", score=" + score +
'}';
}
}
You can use Collections.sort with a custom comparator to sort Persons by descending order of score like this:
List<Person> list = new LinkedList<>(Arrays.asList(new Person("Jack", 3), new Person("Mike", 9)));
System.out.println("before: " + list);
Collections.sort(list, new Comparator<Person>() {
@Override
public int compare(Person o1, Person o2) {
return o2.score - o1.score;
}
});
System.out.println("after: " + list);
This will output:
before: [Person{name='Jack', score=3}, Person{name='Mike', score=9}] after: [Person{name='Mike', score=9}, Person{name='Jack', score=3}]
Along with other answers, here is a neat Java 8 solution:
Collections.sort(list, Comparator.comparingInt(obj -> obj.score).reversed());
The reversed() is for descending order, and this compares by obj.score.
As noted by Iaune, obj -> obj.score can be replaced by ObjType::getScore if you are using Encapsulation correctly.
Collections.sort(List) works for Objects as long as Objects are comparable to one another either through java.lang.Comparable or java.util.Comparator.Since your Objects need custom sorting,you need to implement a comparator
Collections.sort(list,new Comparator(){
@Override
public int compare(MyObject obj1,MyObject obj2){
return obj2.score - obj1.score;
}
});
LinkedHashMap? LinkedList doesn't have K, V pairs.List,MapandSet. What you described is aMap, which contains a Key (String name) and a corresponding Value (int score).LinkedList<TeamDescription>whereTeamDescriptionis a class withStringandint