I defined List<Integer> stack = new ArrayList<Integer>();
我定义了List
When I'm trying to convert it to an array in the following way:
当我试图通过以下方式将其转换为数组时：
Integer[] array= stack.toArray();
I get this exception:
我得到这个例外：
Exception in thread "main" java.lang.Error: Unresolved compilation problem:
Type mismatch: cannot convert from Object[] to Integer[].
Why? It is exactly the same type- Integer to Integer. It's not like in this generic case when the classes are father-and-son relation
为什么？它与Integer完全相同 - Integer。当这些类是父子关系时，它不像这种通用情况
I tried to do casting:
我试着做铸造：
Integer[] array= (Integer[]) stack.toArray();
But here I get this error:
但在这里我得到这个错误：
Exception in thread "main" java.lang.ClassCastException: [Ljava.lang.Object; cannot be cast to [Ljava.lang.Integer;
What is the problem?
问题是什么？
3 个解决方案
#1
11
Because of type erasure, the ArrayList does not know its generic type at runtime, so it can only give you the most general Object[]. You need to use the other toArray method which allows you to specify the type of the array that you want.
由于类型擦除，ArrayList在运行时不知道它的泛型类型，因此它只能为您提供最通用的Object []。您需要使用另一个toArray方法，该方法允许您指定所需的数组类型。
Integer[] array= stack.toArray(new Integer[stack.size()]);
#2
2
The way to do it is this:
这样做的方法是这样的：
Integer[] array = stack.toArray(new Integer[stack.size()]);
For the record, the reason that your code doesn't compile is not just type erasure. The problem is that List<T>.toArray() returns an Object[] and it has done this before generics were introduced.
对于记录，您的代码不编译的原因不仅仅是类型擦除。问题是List
#3
1
Do this instead:
改为：
Integer[] array = stack.toArray(new Integer[stack.size()]);
We need to pass the "seed" array as an argument to the toArray method.
我们需要将“seed”数组作为参数传递给toArray方法。
#1
11
Because of type erasure, the ArrayList does not know its generic type at runtime, so it can only give you the most general Object[]. You need to use the other toArray method which allows you to specify the type of the array that you want.
由于类型擦除，ArrayList在运行时不知道它的泛型类型，因此它只能为您提供最通用的Object []。您需要使用另一个toArray方法，该方法允许您指定所需的数组类型。
Integer[] array= stack.toArray(new Integer[stack.size()]);
#2
2
The way to do it is this:
这样做的方法是这样的：
Integer[] array = stack.toArray(new Integer[stack.size()]);
For the record, the reason that your code doesn't compile is not just type erasure. The problem is that List<T>.toArray() returns an Object[] and it has done this before generics were introduced.
对于记录，您的代码不编译的原因不仅仅是类型擦除。问题是List
#3
1
Do this instead:
改为：
Integer[] array = stack.toArray(new Integer[stack.size()]);
We need to pass the "seed" array as an argument to the toArray method.
我们需要将“seed”数组作为参数传递给toArray方法。