线性表

class List<E> {
    private final int capacity;
    private int size;
    private boolean isInit = false;
    private Object[] elementData;
    /**
     * 后移元素
     * */
    private void moveToNextElement(int start, int end) {
        for (int i = 0; i < end - start; i++) {
            this.elementData[end - i] = this.elementData[end - i - 1];
        }
    }

    /**
     * 前移元素
     * */
    private void moveToHeadElement(int start, int end) {
        for (int i = 0; i < end - start; i++) {
            this.elementData[start + i] = this.elementData[start + i + 1];
        }
    }

    private boolean isIllegal(int index) {
        return index < 0 || index > size;
    }

    public List(int initialCapacity) {
        this.capacity = initialCapacity;
        this.size = 0;
    }

    /**
     * 线性表是否已满
     */
    private boolean isFull() {
        return this.size == capacity - 1;
    }

    /**
     * 线性表是否为空
     */
    public boolean isEmpty() {
        return this.size == 0;
    }


    /**
     * 获取最大容量
     */
    public int getCapacity() {
        return capacity;
    }

    /**
     * 获取当前长度
     */
    public int getSize() {
        return this.size;
    }

    /**
     * 插入元素
     */
    public boolean insertData(int index, E element) {
        if (isIllegal(index) || isFull()) {
            return false;
        }
        if (!isInit) {
            this.elementData = new Object[capacity];
            isInit = true;
        }
        moveToNextElement(index + 1, this.size);
        this.elementData[index] = element;
        this.size++;
        return true;
    }

    /**
     * 追加元素
     */
    public boolean appendElement(E element) {
        if (isFull()) {
            return false;
        }
        if (!isInit) {
            this.elementData = new Object[capacity];
            isInit = true;
        }
        this.elementData[this.size] = element;
        this.size++;
        return true;
    }

    /**
     * 清空顺序表
     */
    public void clear() {
        this.size = 0;
    }

    /**
     * 删除指定索引元素
     */
    public E removeElement(int index) {
        if (isEmpty() || isIllegal(index)) {
            return null;
        }
        E ele = get(index);
        moveToHeadElement(index, this.size);
        size--;
        return ele;
    }

    /**
     * 获取某个索引上的元素
     */
    @SuppressWarnings("unchecked")
    public E get(int index) {
        if (isIllegal(index)) {
            return null;
        }
        return (E) this.elementData[index];
    }

    @Override
    public String toString() {
        Object[] list = new Object[size];
        System.arraycopy(this.elementData, 0, list, 0, size);
        return Arrays.toString(list);
    }
}