Convert ArrayList<String> to String[] array [duplicate]

Solution 1:

Use like this.

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);

Solution 2:

Try this

String[] arr = list.toArray(new String[list.size()]);

Solution 3:

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]);

For more details, refer to the javadocs for the two overloads of List.toArray.

The latter version uses the zero-length array to determine the type of the result array. (Surprisingly, it is faster to do this than to preallocate ... at least, for recent Java releases. See https://stackoverflow.com/a/4042464/139985 for details.)

From a technical perspective, the reason for this API behavior / 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 to hold the list elements, it is used. Otherwise a new array of the same type and a larger size is 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.}

Solution 4:

An alternative in Java 8:

String[] strings = list.stream().toArray(String[]::new);