DotNet 原始碼學習——QUEUE-有解無憂

1、Queue宣告創建物件，(Queue為泛型物件，)

public class Queue<T> :IEnumerable<T>,System.Collections.ICollection,IReadOnlyCollection<T>

本質為Array物件存盤資料，

Queue<string> qy = new Queue<string>();
private T[] _array
public Queue()
{
    _array = Array.Empty<T>();
}
Queue<int> qy1 = new Queue<int>(12);
public Queue(int capacity)
{
    if (capacity < 0)
        throw new ArgumentOutOfRangeException(nameof(capacity), capacity, SR.ArgumentOutOfRange_NeedNonNegNum);
    _array = new T[capacity];
}

Queue<int> qy2 = new Queue<int>(new List<int>());

public Queue(IEnumerable<T> collection)
{
    if (collection == null)
        throw new ArgumentNullException(nameof(collection));

    _array = EnumerableHelpers.ToArray(collection, out _size);
    if (_size != _array.Length) _tail = _size;
}

2、佇列的空間是實際存盤值的兩倍，如果小于兩倍則每次增場4的長度，

1 if (_size == _array.Length)
2 {
3      int newcapacity = (int)((long)_array.Length * (long)GrowFactor / 100);
4      if (newcapacity < _array.Length + MinimumGrow)
5      {
6          newcapacity = _array.Length + MinimumGrow;
7      }
8      SetCapacity(newcapacity);
9 }

3、Queue為先進先出，

進佇列在陣列末尾賦值

        public void Enqueue(T item)
        {
            if (_size == _array.Length)
            {
                int newcapacity = (int)((long)_array.Length * (long)GrowFactor / 100);
                if (newcapacity < _array.Length + MinimumGrow)
                {
                    newcapacity = _array.Length + MinimumGrow;
                }
                SetCapacity(newcapacity);
            }

            _array[_tail] = item;
            MoveNext(ref _tail);
            _size++;
            _version++;
        }

出佇列則從頭部取值

        public T Dequeue()
        {
            int head = _head;
            T[] array = _array;

            if (_size == 0)
            {
                ThrowForEmptyQueue();
            }

            T removed = array[head];
            if (RuntimeHelpers.IsReferenceOrContainsReferences<T>())
            {
                array[head] = default!;
            }
            MoveNext(ref _head);
            _size--;
            _version++;
            return removed;
        }

4、TryDequeue 與 Dequeue()區別在于 TryDequeue 判斷size為0時，回傳false 并out 泛型的默認值

        public bool TryDequeue([MaybeNullWhen(false)] out T result)
        {
            int head = _head;
            T[] array = _array;

            if (_size == 0)
            {
                result = default!;
                return false;
            }

            result = array[head];
            if (RuntimeHelpers.IsReferenceOrContainsReferences<T>())
            {
                array[head] = default!;
            }
            MoveNext(ref _head);
            _size--;
            _version++;
            return true;
        }

注：MaybeNullWhenAttribute(Boolean) 回傳值條件，如果方法回傳此值，則關聯的引數可能為 null

5、Peek 僅僅時查看一下下一個要回傳的值，不從陣列移除

            if (_size == 0)
            {
                result = default!;
                return false;
            }

            result = _array[_head];
            return true;

隨是拙見，但為原創，轉載注明出處，敬謝

Queue 常用的方法大約就這些，先寫道這里，碎覺，

以下為公眾號，一起學起來~

轉載請註明出處，本文鏈接：https://www.uj5u.com/net/64913.html

標籤：.NET Core

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