如何使用泛型实现比较器? [英] How do I implement a Comparator using Generics?

问题描述

Arraylist 只是一个小问题.我想按名称对 ArrayList< Client> 进行排序.

Just a minor problem with Arraylist. I want to sort a ArrayList<Client> by name.

Class Client{ String name; int phonenumber ..}

此代码可以完成工作，但是我收到了编译器警告:使用未经检查或不安全的操作".有什么问题吗?

This code does the work, but i'm having a compiler warning: "uses unchecked or unsafe operations". Whats the problem?

 public void sortByName(){
    Collections.sort(ListofClients, new NameComparator());
 }

我的比较器如下:

public class NameComparator implements Comparator{
  public int compare(Object client1, Object client) {
   String name1 = ((Client) client1).getName();
   String name2 = ((Client) client2).getName();

   return name1.toUpperCase()).compareTo(name2.toUpperCase(); 
  }
}

如果我使用" implements Comparator< Client> "，则会出现错误:"NameComparator不是抽象的，并且不会覆盖java.util.Comparator中的抽象方法compare(Client，Client).我的比较器错了吗?对这个新手问题很抱歉，这是Java的新手

If i use "implements Comparator<Client> " i get a error: "NameComparator is not a abstract and does not override abstract method compare(Client, Client) in java.util.Comparator. Is my comparator wrong? sorry for this noob question, new to java

推荐答案

实现比较器< Client> 后，您需要进行以下更改:

After you implement Comparator<Client> you need to change:

public int compare(Object client1, Object client) 
{
  ...
}

对此

public int compare(Client client1, Client client)
{
    // Now you don't have to cast your objects!
}

这都是因为比较器的定义

this is all because the definition of comparator

public interface Comparator<T>
{
    public compare(T o1, T o2);
}

注意方法名称中通用参数T的显示方式.

Notice how the generic parameter T shows up in the method name.

在这种情况下，像Eclipse/Netbeans/IntelliJ这样的IDE会有所帮助.

An IDE like Eclipse / Netbeans / IntelliJ will help out in this situation.

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