将通用列表转换为数组 [英] Convert a generic list to an array

问题描述

 类Helper {
 public static< T> T [] toArray（List< T> list）{
 T [] array =（T []）new Object [list.size（）]; 
 for（int i = 0; i< list.size（）; i ++）{
 array [i] = list.get（i）; 
} 
返回数组; 
 
 
 $ / code> 

测试：



  public static void main（String [] args）{
 List< String> list = new ArrayList< String>（）; 
 list.add（abc）; 
 String [] array = toArray（list）; 
 System.out.println（array）; 
} 
  

但引发错误：



 线程main中的异常java.lang.ClassCastException：[Ljava.lang.Object;不能转换为[Ljava.lang.String; 
 at test.Helper.main（Helper.java:30）
  

如何解决这个问题？


$ b

更新



我想要这个方法，因为有时候，我的代码中的类型太长了：
$ b $ $ p $ newEntries.toArray（new IClasspathEntry [0] ）


我希望打电话：



  toArray（newEntries）
  





---

FINALLY

似乎不可能创建这样一种方法，非常感谢大家！

解决方案

您可以直接致电 list.toArray（T [] array） 并且不必担心关于自己实现它，但正如aioobe所说，由于类型擦除，您不能创建一个泛型类型的数组。如果您需要返回该类型，则需要自己创建一个类型化实例并将其传入。

I have searched for this, but unfortunately, I don't get the correct answer.

class Helper {
    public static <T> T[] toArray(List<T> list) {
        T[] array = (T[]) new Object[list.size()];
        for (int i = 0; i < list.size(); i++) {
            array[i] = list.get(i);
        }
        return array;
    }
}

Test it:

public static void main(String[] args) {
    List<String> list = new ArrayList<String>();
    list.add("abc");
    String[] array = toArray(list);
    System.out.println(array);
}

But there is an error thrown:

Exception in thread "main" java.lang.ClassCastException: [Ljava.lang.Object; cannot be cast to [Ljava.lang.String;
at test.Helper.main(Helper.java:30)

How to solve this?

---

UPDATE

I want this method, because sometimes, the type in my code is too long:

newEntries.toArray(new IClasspathEntry[0])

I'd hope to call:

toArray(newEntries)

---

FINALLY

It seems impossible to create such a method, thank you all very much!

解决方案

You can just call list.toArray(T[] array) and not have to worry about implementing it yourself, but as aioobe said, you can't create an array of a generic type due to type erasure. If you need that type back, you need to create a typed instance yourself and pass it in.

这篇关于将通用列表转换为数组的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！