Java动态数组的实现过程

public class MyList {
    private int[] arr;        // 底层数组
    private int capacity = 10; // 数组容量
    private int size = 0;     // 当前元素个数
    private int extendRatio = 2; // 扩容倍数
}

public int size() {
    return size;
}

public int capacity() {
    return capacity;
}

public int get(int index) {
    if (index < 0 || index >= size) {
        throw new IndexOutOfBoundsException();
    }
    return arr[index];
}

public void set(int index, int num) {
    if (index < 0 || index >= size) {
        throw new IndexOutOfBoundsException();
    }
    arr[index] = num;
}

public void add(int item) {
    if (size == capacity) {
        extendCapacity();
    }
    arr[size] = item;
    size++;
}

public void insert(int index, int item) {
    if (index < 0 || index >= size) {
        throw new IndexOutOfBoundsException();
    }
    if (size == capacity) {
        extendCapacity();
    }
    // 将index后的元素都向后移动一位
    for (int i = size - 1; i >= index; i--) {
        arr[i + 1] = arr[i];
    }
    arr[index] = item;
    size++;
}

public int remove(int index) {
    if (index < 0 || index >= size) {
        throw new IndexOutOfBoundsException();
    }
    int num = arr[index];
    // 将index后的元素都向前移动一位
    for (int i = index; i < size - 1; i++) {
        arr[i] = arr[i + 1];
    }
    size--;
    return num;
}

private void extendCapacity() {
	// 新建一个长度为原数组 extendRatio 倍的新数组，并将原数组复制到新数组
    arr = Arrays.copyOf(arr, extendRatio);
    // 更新列表容量
    capacity = arr.length;
}