Question

我正在尝试创建一个以迭代方式计算数字序列的程序。我很难为我的长体定义动态长度数组。当使用下面的我得到“数组维度丢失”。我在这里错过明显的东西吗？

谢谢

long seq[] = new long[];

完整代码：

public long calculate(long n) {
        // If n is one of known values return that value
        if(n<=1){
            return 0;
        }
        if(n==2){
            return 1;
        }
        if (n==3){
            return 2;
        }

        // initate array to calculate
        long seq[] = new long[];
        int x = 0;
        seq[0] = 0;
        seq[1] = 0;
        seq[2] = 1;
        seq[3] = 2;

        // for loop until reached requested number
        for (int i = 4; i<=n; i++){
            seq[i] = seq[i-1]+seq[i-3];
        }
        for (int i =0; i<n; i++){
            x++;
        }
        return seq[x];
    }

Answer 1

您不能编码

long seq[] = new long[];

像这样！必须有一个初始容量。

请参阅ArrayList源：

/**
     * The array buffer into which the elements of the ArrayList are stored.
     * The capacity of the ArrayList is the length of this array buffer. Any
     * empty ArrayList with elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA
     * will be expanded to DEFAULT_CAPACITY when the first element is added.
     */
    transient Object[] elementData; // non-private to simplify nested class access
    
    /**
     * Constructs an empty list with the specified initial capacity.
     *
     * @param  initialCapacity  the initial capacity of the list
     * @throws IllegalArgumentException if the specified initial capacity
     *         is negative
     */
    public ArrayList(int initialCapacity) {
        if (initialCapacity > 0) {
            this.elementData = new Object[initialCapacity];
        } else if (initialCapacity == 0) {
            this.elementData = EMPTY_ELEMENTDATA;
        } else {
            throw new IllegalArgumentException("Illegal Capacity: "+
                                               initialCapacity);
        }
    }

    /**
     * Constructs an empty list with an initial capacity of ten.
     */
    public ArrayList() {
        this.elementData = DEFAULTCAPACITY_EMPTY_ELEMENTDATA;
    }

如果要动态插入：

/**
     * Inserts the specified element at the specified position in this
     * list. Shifts the element currently at that position (if any) and
     * any subsequent elements to the right (adds one to their indices).
     *
     * @param index index at which the specified element is to be inserted
     * @param element element to be inserted
     * @throws IndexOutOfBoundsException {@inheritDoc}
     */
    public void add(int index, E element) {
        rangeCheckForAdd(index);

        ensureCapacityInternal(size + 1);  // Increments modCount!!
        System.arraycopy(elementData, index, elementData, index + 1,
                         size - index);
        elementData[index] = element;
        size++;
    }

Answer 2

缺少维度是因为，当您编写[n]时，它是一个维度，而当您编写[n,m]时，则是二维，并且这样向前发展...

当您刚刚传递空的[]时。它对填充数组的方式一无所知，因此您需要像这样long[] powers = {..., 2863245995L, 11453115051L, ...};来填充它 long[] powers = {..., 2863245995L, 11453115051L, ...};

或设置尺寸，这也意味着您需要设置尺寸。因为，您需要使用数字或逗号分隔的数字列表，每个数字代表每个维度的大小。像：long[] heights = new long[4];

如果要强制将其设置为数组，但又要动态更改其大小... C＃List这样做，我个人认为，JAVA ArrayList应该是相同的：

Initialize:
  create a array of default minimum size which is power of 2, 
  Set a used element count with name such as Count/Length to the number of element that are initially loaded otherwise 0

Adding element: 
  if there is more space, add to free slot, 
  if not, create new array and double the size
    then copy all item to the new array.
  Add to the Count/Length of array

否则，LinkedList会完成这项工作，您应该已经知道它是如何工作的...

定义长数组动态长度

2 个答案: