Convert ArrayList<String> to String[] array
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像这样使用。
List<String> stockList = new ArrayList<String>();
stockList.add("stock1");
stockList.add("stock2");
String[] stockArr = new String[stockList.size()];
stockArr = stockList.toArray(stockArr);
for(String s : stockArr)
System.out.println(s);
尝试这个
String[] arr = list.toArray(new String[list.size()]);
What is happening is that stock_list.toArray() is creating an Object[] rather than a String[] and hence the typecast is failing1.
The correct code would be:
String [] stockArr = stockList.toArray(new String[stockList.size()]);
or even
String [] stockArr = stockList.toArray(new String[0]);
(Surprisingly, the latter version is faster in recent Java releases: see https://stackoverflow.com/a/4042464/139985)
For more details, refer to the javadocs for the two overloads of List.toArray .
(From a technical perspective, the reason for this API behaviour / design is that an implementation of the List<T>.toArray() method has no information of what the <T> is at runtime. All it knows is that the raw element type is Object . By contrast, in the other case, the array parameter gives the base type of the array. (If the supplied array is big enough, it is used. Otherwise a new array of the same type and a larger size will be allocated and returned as the result.)
1 - In Java, an Object[] is not assignment compatible with a String[] . If it was, then you could do this:
Object[] objects = new Object[]{new Cat("fluffy")};
Dog[] dogs = (Dog[]) objects;
Dog d = dogs[0]; // Huh???
This is clearly nonsense, and that is why array types are not generally assignment compatible.
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