Why isn't Collections.binarySearch() working with this comparable?

Question

I have this Player class which implements the Comparable interface. Then I have an ArrayList of Players. I'm trying to use binarySearch() on the list of Players to find one Player, but Java is giving me a "cannot find symbol: method binarySearch(java.util.ArrayList< Player>,Player)".

This the Player class:

class Player implements Comparable {

    private String username;
    private String password;
    Statistics stats;

    //Constructor, creates a new Player with a supplied username
    Player(String name) {
        username = name;
        password = "";
        stats = new Statistics();
    }

    //Accessor method to return the username as a String
    String getName() {
        return username;
    }

    String getPassword() {
        return password;
    }

    void setPassword(String newPass) {
        password = newPass;
    }

    //Method to change the username
    void setName(String newName) {
        username = newName;
    }

    public int compareTo(Object o) {
        return username.compareTo(((Player)o).username);
    }
}

Weird thing, when I try Collections.sort() on this same list, it works.

Answer 1

Use are using generics inconsistently. Take heed of the compiler warnings. Always supply generic arguments (or never supply them).

Instead of:

class Player implements Comparable {
    [...]
    public int compareTo(Object o) {

Use

class Player implements Comparable<Player> {
    [...]
    public int compareTo(Player o) {

The rules of generics are difficult enough without the complication of rare types. So, typically the language spec gives up if you mix them up.