I have an arrayList of different types of players based on sports. I need to sort the list of players in the arrayList by last name to start. If 2 players have the same last name it needs to then sort those 2 players by the first name. example: Format Lastname firstname
Williams Robert
Phillips Warren
Doe John
Phillips Mark
Output should be
Doe John
Phillips Mark
Phillips Warren
Williams Robert
What I have now only sorts by either the first or last. I have it by last atm in my code.
public static void sortPlayers(ArrayList playerList) {
for (int i = 0; i < playerList.size(); i++) {
for (int j = 0; j < playerList.size(); j++) {
Collections.sort(playerList, new Comparator() {
public int compare(Object o1, Object o2) {
PlayerStats p1 = (PlayerStats) o1;
PlayerStats p2 = (PlayerStats) o2;
开发者_StackOverflow中文版 return p1.getPlayerLastName().compareToIgnoreCase(p2.getPlayerLastName());
}
});
}
}
}
Change the comparator to:
public int compare(Object o1, Object o2) {
PlayerStats p1 = (PlayerStats) o1;
PlayerStats p2 = (PlayerStats) o2;
int res = p1.getPlayerLastName().compareToIgnoreCase(p2.getPlayerLastName());
if (res != 0)
return res;
return p1.getPlayerFirstName().compareToIgnoreCase(p2.getPlayerFirstName())
}
Petar's answer is correct, just two remarks:
- Use
List
instead ofArrayList
as method argument, as the interface is more general, and the method will work even if you change to anotherList
type (likeLinkedList
... ) later - Use generics to make your code more type safe.
An improved version:
//the place where you define the List
List<PlayerStats> playerList = new ArrayList<PlayerStats>();
public static void sortPlayers(List<PlayerStats> playerList) {
Collections.sort(playerList, new Comparator<PlayerStats>() {
public int compare(PlayerStats p1, PlayerStats p2) {
int res = p1.getPlayerLastName().compareToIgnoreCase(p2.getPlayerLastName());
if (res != 0)
return res;
return p1.getPlayerFirstName().compareToIgnoreCase(p2.getPlayerFirstName())
}
});
}
Using java8 there is easy way to do this:
public List<PlayerStats> getSortedPlayerList(List<PlayerStats> playerList) {
return playerList.stream().sorted(Comparator.comparing(PlayerStats::getPlayerLastName).thenComparing(PlayerStats::getPlayerFirstName)).collect(Collectors.toList());
}
//requires java@8
//class Person { String fName; String lName; int id}
List<Person> list = new ArrayList<>();
Person p1 = new Person();
p1.setfName("a");
p1.setlName("x");
list.add(p1 );
Person p4 = new Person();
p4.setfName("b");
p4.setlName("z");
list.add(p4);
Person p3 = new Person();
p3.setfName("a");
p3.setlName("z");
list.add(p3);
Person p2 = new Person();
p2.setfName("a");
p2.setlName("y");
list.add(p2);
//sort by a single field
Collections.sort(list, (o1,o2) -> o1.getfName().compareTo(o2.getfName()));
//sort by multiple cascading comparator.
Collections.sort(list, Comparator.comparing(Person::getfName).thenComparing(Person::getlName));
list.forEach( System.out::println);
//output
//Person [fName=a, lName=x, id=null]
//Person [fName=a, lName=y, id=null]
//Person [fName=a, lName=z, id=null]
//Person [fName=b, lName=z, id=null]
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