初始化列表< T>给定数量的空值而没有循环? [英] Initializing List<T> with given number of nulls without loop?

问题描述

是否可以将List<T>初始化为包含给定数量的null，其中T是列表是其成员的类的类型参数?我当然可以通过循环来做到这一点，但想知道是否可以不这样做.

Can a List<T> be initialized to contain a given number of nulls, where T is a type parameter of the class of which the list is a member? I sure can do it with a loop, but like to know whether it is possible without.

List<T> myList = new ArrayList<T>(numEls);

创建一个给定容量但大小为0的列表，因此对于所有x，myList.get(x)均失败，例如. myList.set(numEls-1,null).

creates a list of the given capacity, but size 0, so myList.get(x) fails for all x, and so does, e.g. myList.set(numEls-1,null).

myList = Arrays.asList(new T[numEls]);

不编译，并且

 myList = (List<T>) Arrays.asList(new Object[numEls]);

在Eclipse中进行编译(带有未选中的强制转换警告)，但不能在javac中进行编译.

compiles in Eclipse (with an Unchecked cast warning), but not with javac.

更新:谢谢您的回答！但是，我找到了另一个很短的解决方案，接近于我上一次尝试的解决方案，该解决方案可以在eclipse中使用我们的自动构建系统进行编译:对数组进行广播，而不对列表进行广播！

Update: Thank you for the answers! However, I found another, quite short, solution close to my last attempt above, which compiles both in eclipse and with our automated build system: Cast the array, not the list!

myList = Arrays.asList((T[]) new Object[numEls]);

推荐答案

如果您想要ArrayList，则可以使用反射来作弊

if you want an ArrayList you can use reflection to cheat

ArrayList<T> myList = new ArrayList<T>(numEls);
Field f = ArrayList.class.getField("size");//cache this
f.setAccessible(true);
f.setInt(myList, numEls);

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