我想写一个方法list->array 想利用泛型，代码如下
public static <T> T[] list2Array(List<T> list){ T[] array = (T[])list.toArray(new T[list.size()]); return array;}也就是传过来的String就返回String数组 Integer就返回Integer数组。但是这个new T[list.size]这里有问题，请问怎么解决？谢谢。
解决方案
这个Effective Java第二版里有说到, Item25.
Because of these fundamental differences, arrays and generics do not
mix well. For example, it is illegal to create an array of a generic
type, a parameterized type, or a type parameter. None of these array
creation expressions are legal: new List[], new List [], new
E[]. All will result in generic array creation errors at compile time.Generally speaking, arrays and generics don’t mix well. If you find
yourself mixing them and getting compile-time errors or warnings, your
first impulse should be to replace the arrays with lists.
- 因为数组和泛型不对付, 所以在不做强制类型转换的情况下, 我们是没有办法得到一个泛型数组的实例的, 编译器会限制此类情况发生(new E[], list.toArray());
- 为什么数组和泛型不对付, Effective Java里有例子. 根本原因在于:
Arrays are covariant. This scary-sounding word means simply that if
Sub is a subtype of Super, then the array type Sub[] is a subtype of
Super[].
给出例子说明我的理解, 类似的代码, 在泛型集合下, 会在静态编译阶段报错; 而泛型数组在运行阶段给出ArrayStoreException:
private <T> void doSomethingToGenArr(T[] tArr){ Object[] oArr = tArr; oArr[0] = new String("aaa");}private <T> void doSomethingToGenList(List<T> list){ List<Object> l1 = list; /* compile error */ l1.set(0, new String("aaa"));}@Testpublic void test111(){ doSomethingToGenArr(new Integer[2]);}@Testpublic void test112(){ doSomethingToGenList(new ArrayList<Integer>());}