在c#中,数组列表和List<>有什么区别?
是不是只有List<>有类型而ArrayList没有?
在c#中,数组列表和List<>有什么区别?
是不是只有List<>有类型而ArrayList没有?
当前回答
To me its all about knowing your data. If I am continuing to expand my code on the basis of efficiency, I would have to choose the List option as a way of deciphering of my data w/o the unnecessary step of always wondering about types, especially 'Custom Types'. If the machine understands the difference and can determine on it's on what type of data I'm actually dealing with then why should I get in the way and waste time going thru the gyrations of 'IF THEN ELSE' determinations? My philosophy is to let the machine work for me instead of me working on the machine? Knowing the unique differences of different object code commands goes a long way in making your code as efficient.
汤姆•约翰逊 (一项…一个出口)
其他回答
使用“List”可以防止强制转换错误。它对于避免运行时强制转换错误非常有用。
例子:
在这里(使用ArrayList),您可以编译这段代码,但稍后会看到一个执行错误。
// Create a new ArrayList
System.Collections.ArrayList mixedList = new System.Collections.ArrayList();
// Add some numbers to the list
mixedList.Add(7);
mixedList.Add(21);
// Add some strings to the list
mixedList.Add("Hello");
mixedList.Add("This is going to be a problem");
System.Collections.ArrayList intList = new System.Collections.ArrayList();
System.Collections.ArrayList strList = new System.Collections.ArrayList();
foreach (object obj in mixedList)
{
if (obj.GetType().Equals(typeof(int)))
{
intList.Add(obj);
}
else if (obj.GetType().Equals(typeof(string)))
{
strList.Add(obj);
}
else
{
// error.
}
}
如.NET Framework文档中所述
我们不建议你将数组列表类用于new 发展。相反,我们建议您使用通用的List<T> 类。ArrayList类被设计用来保存异构类 对象的集合。然而,它并不总是提供最好的 的性能。相反,我们建议如下: 对于异构对象集合,使用List<Object>(在c#中)或List(of Object)(在Visual Basic中)类型。 对于对象的同构集合,使用List<T>类。
请参见不应使用非泛型集合
ArrayList是不同类型数据的集合,而List<>是其自身依赖的相似类型数据的集合。
我认为,ArrayList和List<T>之间的区别是:
List<T>, where T is value-type is faster than ArrayList. This is because List<T> avoids boxing/unboxing (where T is value-type). Many sources say - usually ArrayList used just for backward compatibility. (is not a real difference, but i think it is important note). Reflection is easier with nongeneric ArrayList then List<T> ArrayList has IsSynchronized property. So, It is easy to create and use syncronised ArrayList. I didin't found IsSynchronized property for List<T>. Also Keep in mind this type of synchronization is relatively inefficient, msdn): var arraylist = new ArrayList(); var arrayListSyncronized = ArrayList.Synchronized(arraylist Console.WriteLine($"syncronized {arraylist.IsSynchronized}"); Console.WriteLine($"syncronized {arrayListSyncronized.IsSynchronized}"); var list = new List<object>(); var listSyncronized = ArrayList.Synchronized(list); Console.WriteLine($"syncronized {list.IsSynchronized}");//error, no such prop Console.WriteLine($"syncronized {list.IsSynchronized}");//error, no such prop ArrayList has ArrayList.SyncRoot property which can be used for syncronisation (msdn). List<T> hasn't SyncRoot property, so in the following construction you need to use some object if you use List<T>: ArrayList myCollection = new ArrayList(); lock(myCollection.SyncRoot) // ofcourse you can use another object for this goal { foreach (object item in myCollection) { // ... } }
简单的答案是,
数组列表是非泛型的
它是一个对象类型,因此您可以在其中存储任何数据类型。 可以在数组列表中存储任意值(值类型或引用类型),例如string、int、employee和object。(注意,) 装箱和开箱将会发生。 不类型安全。 它更老。
列表是通用的
它是类型的类型,因此您可以在运行时指定T。 根据声明,您只能存储类型为T的值(字符串或int或employee或object)。(注意或) 装箱和开箱不会发生。 类型安全。 它更新。
例子:
ArrayList arrayList = new ArrayList();
List<int> list = new List<int>();
arrayList.Add(1);
arrayList.Add("String");
arrayList.Add(new object());
list.Add(1);
list.Add("String"); // Compile-time Error
list.Add(new object()); // Compile-time Error
请阅读微软官方文档:https://blogs.msdn.microsoft.com/kcwalina/2005/09/23/system-collections-vs-system-collection-generic-and-system-collections-objectmodel/
注意:在理解它们的区别之前,您应该了解泛型:https://learn.microsoft.com/en-us/dotnet/csharp/programming-guide/generics/