java - 如何在 Java 中删除 Array Generic 对象 Sack

Question

因此，我正在创建一个名为“Sack”的通用数据结构。在此，我将元素添加到麻袋中，抓取随机元素，查看它是否为空，或转储其内容等。此外，我还创建它来扩展以容纳所需数量的元素。

删除辅助方法应该删除底层数据结构中的项目指定索引。它应该通过将其替换为底层数组中的“最后一个”元素来实现。它还应该确保任何未使用的元素都无效。

目前，我正在研究删除方法，但我的删除方法遇到了麻烦。当我运行测试时，我收到错误，说它没有正确的修饰符。因此我的代码是

public class Sack<E>
{
public static final int DEFAULT_CAPACITY = 10;
private E [] elementData;
private int size;

@SuppressWarnings("unchecked")
public Sack()
{
    elementData = (E[]) new Object[DEFAULT_CAPACITY];
}
@SuppressWarnings("unchecked")
public Sack(int capacity)
{
    if(capacity < 0)
    {
        throw new IllegalArgumentException("capacity " + capacity);
    }
    this.elementData = (E[]) new Object[capacity];
}

public boolean isEmpty()
{
    if(size == 0)
    {
        return true;
    }
    else
    {
        return false;
    }
}
public void add(E item)
{
    int index = size++;
    if(size >= elementData.length-1)
    {
        elementData = Arrays.copyOf(elementData, size);
    }
    elementData[index] = item;
}
  public E [] dump()
{
   E [] E2 = Arrays.copyOf(elementData, size);
   for(int i = 0; i < size; i++)
   {
      elementData[i] = null;

   }
   size = 0;
    return E2;
}

我在此处删除时收到错误

 public void remove(int index)
{
    for (int i = index; i < size; i++)
    {
        elementData[i] = elementData[i + 1];
    }
    size--;
}
}

它期望接收的值是 2，但它接收的值是 1。请下拉确保这一点的任何方法。

这是我的测试。我无法修改我的测试，只能修改我的代码。我在第一行收到错误。我会评论一下，让你看看。

@Test
public void testRemove()
{
    assertEquals(2, remove.getModifiers(), "remove does not have the correct modifiers"); // I receive an error here. 
    try
    {
        Random rand = new Random();
        Integer[] setElementData = new Integer[10];
        ArrayList<Integer> expectedElements = new ArrayList<Integer>();
        int randElement;
        for(int i=0; i<10; ++i)
        {
            randElement = rand.nextInt(50) + 1;
            setElementData[i] = randElement;
            expectedElements.add(randElement);
        }
        elementData.set(s, setElementData);
        size.set(s, 10);

        int randIndex;
        int numEe;
        while(!expectedElements.isEmpty()) {
            numEe = expectedElements.size()-1;
            randIndex = rand.nextInt(expectedElements.size());
            expectedElements.set(randIndex, expectedElements.get(numEe));
            expectedElements.remove(numEe);
            remove.invoke(s, randIndex);
            assertEquals(expectedElements.size(), size.get(s), "remove is not working correctly (check size usage)"); //Error now takes place here. 
            for(int i=0; i<expectedElements.size(); ++i) {
                assertEquals(expectedElements.get(i), ((Object[])elementData.get(s))[i], "remove is not working correctly (sack array element order incorrect)");
            }
            assertNull(((Object[])elementData.get(s))[expectedElements.size()], "remove is not working correctly (sack array element not nullified correctly)");
        }
        assertEquals(0, size.get(s), "remove is not working correctly (check size usage)");

    } catch (Exception e) {
        fail("remove is not working correctly");
    }
}

Answer 1

这将保持顺序:

public void remove(final int index) {

    if (index >= size || 0 > index) {

        // TODO better to throw 'new ArrayIndexOutOfBoundsException(index)'
        // when remove illegal index
        return;
    }

    if (index < size - 1) { // move whole array

        System.arraycopy(
                elementData, index + 1, // copy from
                elementData, index, // copy to
                size - index - 1); // copy length
    }

    elementData[--size] = null;
}