java - 如何在 Java 中创建类型变量数组？

Question

在 Java 中可以声明类型变量数组，但我无法创建数组。不可能吗？

class ClassName<T> {
    {
        T[] localVar; // OK
        localVar = new T[3]; // Error: Cannot create a generic array of T
    }
}

Answer 1

Java 中没有通用类型的数组。你可以去 ArrayList

解释:

java中的数组是协变类型。

Java arrays have the property that there types are covariant , which means that an array of supertype references is a supertype of an array of subtype references.That is, Object[] is a supertype of String[] for example. As a result of covariance all the type rules apply that are customary for sub- and supertypes: a subtype array can be assigned to a supertype array variable, subtype arrays can be passed as arguments to methods that expect supertype arrays, and so on and so forth.Here is an example:

Object[] objArr = new String[10];// fine

In contrast, generic collections are not covariant. An instantiation of a parameterized type for a supertype is not considered a supertype of an instantiation of the same parameterized type for a subtype.That is, a LinkedList<Object> is not a super type of LinkedList<String> and consequently a LinkedList<String> cannot be used where a LinkedList<Object> is expected; there is no assignment compatibility between those two instantiations of the same parameterized type, etc.Here is an example that illustrates the difference:

LinkedList<Object> objLst = new LinkedList<String>(); // compile-time error

来源:http://www.angelikalanger.com/Articles/Papers/JavaGenerics/ArraysInJavaGenerics.htm