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我知道靜態方法不能訪問實例字段的字段，它讓我困惑的是：爲什麼非靜態方法可以訪問靜態字段currentID？在下面的代碼中，currentID是靜態字段，getNextID是靜態函數。令人驚訝的是，它通過編譯沒有錯誤。爲什麼非靜態方法可以訪問靜態字段？
public class WorkItem
{
// Static field currentID stores the job ID of the last WorkItem that
// has been created.
private static int currentID;
//Properties.
protected int ID { get; set; }
protected string Title { get; set; }
protected string Description { get; set; }
protected TimeSpan jobLength { get; set; }
public WorkItem()
{
ID = 0;
Title = "Default title";
Description = "Default description.";
jobLength = new TimeSpan();
}
// Instance constructor that has three parameters.
public WorkItem(string title, string desc, TimeSpan joblen)
{
this.ID = GetNextID();
this.Title = title;
this.Description = desc;
this.jobLength = joblen;
}
// Static constructor to initialize the static member, currentID. This
// constructor is called one time, automatically, before any instance
// of WorkItem or ChangeRequest is created, or currentID is referenced.
static WorkItem()
{
currentID = 0;
}
protected int GetNextID()
{
// currentID is a static field. It is incremented each time a new
// instance of WorkItem is created.
return ++currentID;
}
}