Question

所以，通常ArrayList.toArray()会返回Object[]的类型....但是假设它是一个对象Arraylist的{{1}}，如何让Custom返回toArray()而非Custom[]的类型？

Answer 1

像这样：

List<String> list = new ArrayList<String>();

String[] a = list.toArray(new String[0]);

在Java6之前，建议写：

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

因为内部实现无论如何都会重新分配一个大小合适的数组，所以你最好先做好。从Java6开始，首选空数组，请参阅.toArray(new MyClass[0]) or .toArray(new MyClass[myList.size()])?

如果您的列表输入不正确，则需要在调用toArray之前进行强制转换。像这样：

    List l = new ArrayList<String>();

    String[] a = ((List<String>)l).toArray(new String[l.size()]);

Answer 2

它实际上不需要返回Object[]，例如： -

    List<Custom> list = new ArrayList<Custom>();
    list.add(new Custom(1));
    list.add(new Custom(2));

    Custom[] customs = new Custom[list.size()];
    list.toArray(customs);

    for (Custom custom : customs) {
        System.out.println(custom);
    }

这是我的Custom课程： -

public class Custom {
    private int i;

    public Custom(int i) {
        this.i = i;
    }

    @Override
    public String toString() {
        return String.valueOf(i);
    }
}

Answer 3

arrayList.toArray(new Custom[0]);

http://download.oracle.com/javase/7/docs/api/java/util/ArrayList.html#toArray%28java.lang.Object[]%29

Answer 4

将List转换为特定类型的Array（例如Long）的较短版本：

Long[] myArray = myList.toArray(Long[]::new);

Answer 5

我得到了答案......这似乎工作得很好

public int[] test ( int[]b )
{
    ArrayList<Integer> l = new ArrayList<Integer>();
    Object[] returnArrayObject = l.toArray();
    int returnArray[] = new int[returnArrayObject.length];
    for (int i = 0; i < returnArrayObject.length; i++){
         returnArray[i] = (Integer)  returnArrayObject[i];
    }

    return returnArray;
}

Answer 6

@SuppressWarnings("unchecked")
    public static <E> E[] arrayListToArray(ArrayList<E> list)
    {
        int s;
        if(list == null || (s = list.size())<1)
            return null;
        E[] temp;
        E typeHelper = list.get(0);

        try
        {
            Object o = Array.newInstance(typeHelper.getClass(), s);
            temp = (E[]) o;

            for (int i = 0; i < list.size(); i++)
                Array.set(temp, i, list.get(i));
        }
        catch (Exception e)
        {return null;}

        return temp;
    }

样品：

String[] s = arrayListToArray(stringList);
Long[]   l = arrayListToArray(longList);

make arrayList.toArray（）返回更具体的类型

6 个答案: