数组与List之间相互转换的方法详解

List list = new ArrayList();

list.add("1");

list.add("2");

final int size = list.size();

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

public static void main(String[] args){
    int[] a1 = new int[]{1,2,3};
    String[] a2 = new String[]{"a","b","c"};

    System.out.println(Arrays.asList(a1));
    System.out.println(Arrays.asList(a2));
}

1
2 [[I@dc8569]
[a, b, c]

/**
 * @serial include
 */
 private static class ArrayList<E>extends AbstractList<E>implements RandomAccess, java.io.Serializable {
     private static final long serialVersionUID = -2764017481108945198L;
     private final E[] a;

     ArrayList(E[] array) {
         if (array == null)
         throw new NullPointerException();
         a = array;
     }

     public int size() {
        return a.length;
     }

     public Object[] toArray() {
        return a.clone();
     }

     public <T> T[] toArray(T[] a) {
         int size = size();
         if (a.length < size)
            return Arrays.copyOf(this.a, size, (Class<? extends T[]>) a.getClass());
         System.arraycopy(this.a,0, a, 0, size);
         if (a.length > size)
            a[size] = null;
         return a;
     }

     public E get(int index) {
        return a[index];
     }

     public E set(int index, E element) {
         E oldValue = a[index];
         a[index] = element;
         return oldValue;
     }

     public int indexOf(Object o) {
         if (o == null) {
             for (int i = 0; i < a.length; i++)
             if (a[i] == null)
             return i;
         }else {
             for (int i = 0; i < a.length; i++)
             if (o.equals(a[i]))
             return i;
         }
         return -1;
     }

     public boolean contains(Object o) {
        return indexOf(o) != -1;
     }
}

1
2
3 public static <T> List<T> asList(T... a) {
   return new ArrayList<T>(a);
}

public boolean add(E e) {
    add(size(), e);
    return true;
}

public void add(int index, E element) {
    throw new UnsupportedOperationException();
}

public E remove(int index) {
    throw new UnsupportedOperationException();
}