如何实现Iterable接口？ [英] How can I implement the Iterable interface?

问题描述

鉴于以下代码，我如何迭代ProfileCollection类型的对象？

Given the following code, how can I iterate over an object of type ProfileCollection?

public class ProfileCollection implements Iterable {    
    private ArrayList<Profile> m_Profiles;

    public Iterator<Profile> iterator() {        
        Iterator<Profile> iprof = m_Profiles.iterator();
        return iprof; 
    }

    ...

    public Profile GetActiveProfile() {
        return (Profile)m_Profiles.get(m_ActiveProfile);
    }
}

public static void main(String[] args) {
     m_PC = new ProfileCollection("profiles.xml");

     // properly outputs a profile:
     System.out.println(m_PC.GetActiveProfile()); 

     // not actually outputting any profiles:
     for(Iterator i = m_PC.iterator();i.hasNext();) {
        System.out.println(i.next());
     }

     // how I actually want this to work, but won't even compile:
     for(Profile prof: m_PC) {
        System.out.println(prof);
     }
}

推荐答案

Iterable是一个通用的接口。您可能遇到的问题（您实际上没有说过您遇到的问题，如果有的话）是，如果您使用通用接口/类而未指定类型参数，则可以删除不相关的泛型类型的类型在课堂上。这方面的一个例子是对泛型类的非泛型引用会导致非泛型返回类型。

Iterable is a generic interface. A problem you might be having (you haven't actually said what problem you're having, if any) is that if you use a generic interface/class without specifying the type argument(s) you can erase the types of unrelated generic types within the class. An example of this is in Non-generic reference to generic class results in non-generic return types.

所以我至少会将其更改为：

So I would at least change it to:

public class ProfileCollection implements Iterable<Profile> { 
    private ArrayList<Profile> m_Profiles;

    public Iterator<Profile> iterator() {        
        Iterator<Profile> iprof = m_Profiles.iterator();
        return iprof; 
    }

    ...

    public Profile GetActiveProfile() {
        return (Profile)m_Profiles.get(m_ActiveProfile);
    }
}

这应该有效：

for (Profile profile : m_PC) {
    // do stuff
}

如果没有Iterable上的type参数，迭代器可能会被简化为Object类型，所以只有这样才能工作：

Without the type argument on Iterable, the iterator may be reduced to being type Object so only this will work:

for (Object profile : m_PC) {
    // do stuff
}

这是一个非常模糊的Java泛型角落案例。

This is a pretty obscure corner case of Java generics.

如果没有，请提供更多关于什么的信息继续。

If not, please provide some more info about what's going on.

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