为什么Collections.binarySearch（）不能与这个类似？ [英] Why isn't Collections.binarySearch() working with this comparable?

问题描述

我有这个 Player 类实现 Comparable 接口。然后我有一个 ArrayList Player s。我试图在玩家的列表中使用 binarySearch（）找到一个 Player ，但Java给我一个无法找到符号：method binarySearch（java.util.ArrayList< Player>，Player）。 / p>

这是Player类：

  class Player implements Comparable {
 
 private String username; 
 private String password; 
统计数据
 
 //构造函数，使用提供的用户名创建一个新的播放器
 Player（String name）{
 username = name; 
 password =; 
 stats = new Statistics（）; 
} 
 
 //以字符串返回用户名的访问器方法
 String getName（）{
 return username; 
} 
 
 String getPassword（）{
 return password; 
} 
 
 void setPassword（String newPass）{
 password = newPass; 
} 
 
 //改变用户名的方法
 void setName（String newName）{
 username = newName; 
} 
 
 public int compareTo（Object o）{
 return username.compareTo（（Player）o）.username）;奇怪的是，当我尝试Collections.sort（）时，会发生这样的情况：
} 
} 
  

$ b <

解决方案

使用泛型不一致。注意编译器警告。

而不是：

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

使用

  class Player implements可比较的< Player> {
 [...] 
 public int compareTo（Player o）{
  

泛型规则足够困难，没有罕见类型的并发症。所以，通常语言规范放弃，如果你混合它们。

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.

解决方案

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.

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