java - 如何在 Java 中使用数组进行类型泛型？

Question

在 java 中，我想创建一个函数，它接受任何类型内容的列表，然后返回相同类型的数组。我到此为止

public static <T>[] listToArray(List<T> items) {
    <T>[] names = new <T>[items.size()];
    for(int i=0; i<items.size(); i+=1) {
        names[i] = items.get(i);
    }
    return names;
}

但这有很多语法错误...

有人知道怎么做吗？

谢谢

Answer 1

来自 Bloch 的 Effective Java，第 25 项:

...arrays and generics have very different type rules. Arrays are covariant and reified; generics are invariant and erased. As a consequence, arrays provide runtime type safety but not compile-time type safety and vice versa for generics. 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.

解释:

数组是协变的意味着如果 Dog 类扩展 Animal 类，那么您可以:

Animal[] animals = new Animal[5];
animals[0] = new Dog();

这同样不适用于泛型，因为泛型是不变的:

List<Animal> animals = new LinkedList<Animal>();
animals.add(new Dog()); // compilation error!!!

数组被具体化意味着关于数组类型的所有信息在运行时和编译时都是可用的。同样，泛型被删除，这意味着类型信息仅在编译时存在。