Question

这件事只是没有编译。我不知道自己做错了什么。编译器在 Collections.sort（用户）; 咆哮。在程序列表后看到下面的错误消息。如果你能提供任何有关这段代码真正错误的见解，将不胜感激。

这里是 java -version 命令的输出：

java version "1.8.0_25"
Java(TM) SE Runtime Environment (build 1.8.0_25-b18)
Java HotSpot(TM) 64-Bit Server VM (build 25.25-b02, mixed mode)

import java.util.ArrayList;
import java.util.List;
import java.util.Collections;

class MyApp {
    public static void main(String[] args) {

        List<User> users = new ArrayList<>();

        users.add(new User("John Doe"));
        users.add(new User("Bob Smith"));
        users.add(new User("Jane Doe"));
        users.add(new User("Bill Gates"));

        Collections.sort(users);

        for (User user : users)
            System.out.println(user.name);
   }
}

class User implements Comparable<User> {
    public String name;
    User(String name) { this.name = name; }
    @Override public int compareTo(User user) {
        return this.name.compareTo(user.name);
    }
}

这是我收到的丑陋的错误消息：

MyApp.java:15: error: no suitable method found for sort(List<User>)
            Collections.sort(users);
                   ^
    method Collections.<T#1>sort(List<T#1>) is not applicable
      (inference variable T#1 has incompatible bounds
        equality constraints: User
        upper bounds: Comparable<? super T#1>)
    method Collections.<T#2>sort(List<T#2>,Comparator<? super T#2>) is     not appli
cable
      (cannot infer type-variable(s) T#2
        (actual and formal argument lists differ in length))
  where T#1,T#2 are type-variables:
    T#1 extends Comparable<? super T#1> declared in method     <T#1>sort(List<T#1>)
T#2 extends Object declared in method <T#2>sort(List<T#2>,Comparator<?     super
 T#2>)
1 error

Answer 1

您的代码可以使用JDK 1.7.0.60,1.7.0.80,1.8.0.25和1.8.0.40进行编译。可能你有一些早期的1.8.0.x javac，它在泛型方面存在很多问题。尝试将其更新到最新版本。

Answer 2

如果您的编译器抱怨此问题，请尝试提供有关类型的提示：

 Collections.<User>sort(users);

找不到合适的排序方法（List <user>）

2 个答案: