[英]Java Questions Regarding declaring a list of Comparable objects
It is a pretty simple one. 这是一个非常简单的。 I want to declare a list of objects, but I want make sure all objects implemented the Comparable interface.
我想声明一个对象列表,但是我想确保所有对象都实现了Comparable接口。 What should I do?
我该怎么办? I try to write
我尝试写
List<Comparable> heap = new ArrayList<Comparable>();
But compiler gives me a warning. 但是编译器给了我一个警告。 What is the proper way to write it?
编写它的正确方法是什么?
Thanks 谢谢
Follow up: I thought I had finished the question before I post it but apparently I didn't. 跟进:我以为我在发布问题之前已经完成了问题,但显然没有。 So let me finish it up.
所以让我结束它。
My purpose is to have a list of objects that: 1. Implements the Comparable interface 2. Are all with the same type 我的目的是提供一个对象列表:1.实现Comparable接口2.都具有相同的类型
Can I make it 我能做到吗
List<Comparable<?>> heap = new ArrayList<Comparable<?>>()
No, I can't. 不,我不能。 The reason is because I need to retrieve the elements from the list and compare them.
原因是因为我需要从列表中检索元素并进行比较。 like:
喜欢:
if( heap.get(0).compareTo(heap.get(1)) > 0)
If I use wildcard List>, the complier will give me an error. 如果我使用通配符List>,则编译器将给我一个错误。 Saying heap.get(0) cannot match heap.get(1) So I need to know the correct way to declare it.
说heap.get(0)不能匹配heap.get(1),所以我需要知道正确的声明方式。
I find somebody asking me what the warning is.... that surprises me.....well, the warning is: Comparable is a raw type. 我发现有人问我警告是什么...。这让我感到惊讶.....嗯,警告是:可比是原始类型。 References to generic type Comparable should be parameterized
泛型类型Comparable的引用应参数化
It's because you're using the raw type Comparable
. 这是因为您使用的是原始类型
Comparable
。 You can try giving Comparable
a wildcard type parameter: 您可以尝试为
Comparable
提供通配符类型参数:
List<Comparable<?>> heap = new ArrayList<Comparable<?>>();
If you want the objects to all be of the same type, you can do something along the lines of 如果您希望所有对象属于同一类型,则可以按照以下步骤进行操作:
public static <T extends Comparable<? super T>> List<T> getList() {
...
}
and return your list from getList()
. 并从
getList()
返回您的列表。
由于所有对象都是同一类型(例如fe FooType
),因此只需使用List<FooType>
。
Perhaps you could write a method that only takes a type that extends Comparable and returns a List of that type: 也许您可以编写一个只接受扩展Comparable类型并返回该类型List的方法:
public <T extends Comparable> List<T> getComparableList(T t) {
List<T> heap = new ArrayList<T>();
return heap;
}
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