我应该将 ArrayLists 声明/初始化为 <Cat> 的 Lists、ArrayLists 或 ArrayLists 吗? [英] Should I declare/Initialize ArrayLists as Lists, ArrayLists, or ArrayLists of <Cat>

问题描述

声明一个集合有什么区别

What is the difference in declaring a collection as such

public class CatHerder{
    private List cats;
    public CatHerder(){
        this.cats = new ArrayList<Cat>();
    }
}
//or
public class CatHerder{
    private ArrayList cats;
    public CatHerder(){
        this.cats = new ArrayList();
    }
}
//or
public class CatHerder{
    private ArrayList<Cat> cats;
    public CatHerder(){
        this.cats = new ArrayList<Cat>();
    }
}

推荐答案

你应该把它声明为List，并初始化为ArrayList>.

You should declare it as a List<Cat>, and initialize it as an ArrayList<Cat>.

List 是一个接口，ArrayList 是一个实现类.几乎总是最好针对接口而不是实现进行编码.这样，如果您以后需要更改实现，就不会破坏针对接口编码的消费者.

List is an interface, and ArrayList is an implementing class. It's almost always preferable to code against the interface and not the implementation. This way, if you need to change the implementation later, it won't break consumers who code against the interface.

根据您实际使用列表的方式，您甚至可以使用不太具体的 java.util.Collection(List 扩展的接口).

Depending on how you actually use the list, you might even be able to use the less-specific java.util.Collection (an interface which List extends).

至于List(您可以将其读作猫列表")与List:那是Java 的generics，确保编译时类型安全.简而言之，它让编译器确保 List 只包含 Cat 对象.

As for List<Cat> (you can read that as "list of cat") vs List: that's Java's generics, which ensure compile-time type safely. In short, it lets the compiler make sure that the List only contains Cat objects.

public class CatHerder{
    private final List<Cat> cats;
    public CatHerder(){
        this.cats = new ArrayList<Cat>();
    }
}

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