【導(dǎo)讀】不同的設(shè)計(jì)器有很大的沖突，這就才有了EffectiveC#。極大限度上的討論這個(gè)。環(huán)境的好處，須要把你對(duì)本地化環(huán)境的想法改變?yōu)?NetCLR。白.Net的垃圾回收器。在你明白這一章里所推薦的內(nèi)容時(shí)，有必要對(duì).Net的內(nèi)存。不像本地運(yùn)行環(huán)境，你不用負(fù)責(zé)對(duì)內(nèi)存。泄漏，不定指針，未初始化指針，或者一個(gè)其它內(nèi)存管理的服務(wù)問題。收器前不是一個(gè)神話：你一樣要自己清理。柄，數(shù)據(jù)鏈接，GDI+對(duì)象，COM對(duì)象，以及其它一些系統(tǒng)對(duì)象。這有一個(gè)好消息：因?yàn)镚C管理內(nèi)存，明確的設(shè)計(jì)風(fēng)格可以更容易的實(shí)現(xiàn)。循環(huán)引用，不管是簡單關(guān)系還是復(fù)雜的網(wǎng)頁對(duì)象，都非常容易?？蛇_(dá)的，而不是強(qiáng)迫每個(gè)對(duì)象都保持一些引用跟蹤，COM就是這樣的。DataSet是一個(gè)DataTable的集合，而每一個(gè)DataTable又是DataRow的集合，每一個(gè)DataRow又是DataItem的集合，DataColum定義了這些類型的關(guān)系。據(jù)表的順序訪問。對(duì)象的合適的釋放順序，這是GC的工作。在應(yīng)用程序結(jié)束了對(duì)DataSet的引用后，沒有。依懶于析構(gòu)函數(shù)同樣會(huì)導(dǎo)致性能上的損失。

　　

【正文】 ass( int size ) { _coll = new ArrayList( size )。 } } When you create a new MyClass, specifying the size of the collection, you create two array lists. One is immediately garbage. The variable initializer executes before every constructor. The constructor body creates the second array list. The piler creates this version of MyClass, which you would never code by hand. (For the proper way to handle this situation, see Item 14.) public class MyClass { // declare the collection, and initialize it. private ArrayList _coll。 15 MyClass( ) { _coll = new ArrayList( )。 } MyClass( int size ) { _coll = new ArrayList( )。 _coll = new ArrayList( size )。 } } The final reason to move initialization into the body of a constructor is to facilitate exception handling. You cannot wrap the initializers in a TRy block. Any exceptions that might be generated during the construction of your member variables get propagated outside of your object. You cannot attempt any recovery inside your class. You should move that initialization code into the body of your constructors so that you implement the proper recovery code to create your type and gracefully handle the exception (see Item 45). Variable initializers are the simplest way to ensure that the member variables in your type are initialized regardless of which constructor is called. The initializers are executed before each constructor you make for your type. Using this syntax means that you cannot fet to add the proper initialization when you add new constructors for a future release. Use initializers when all constructors create the member variable the same way。 it39。s simpler to read and easier to maintain. Item 13: Initialize Static Class Members with Static Constructors You know that you should initialize static member variables in a type before you create any instances of that type. C lets you use static initializers and a static constructor for this purpose. A static constructor is a special function that executes before any other methods, variables, or properties defined in that class are accessed. You use this function to initialize static variables, enforce the singleton pattern, or perform any other necessary work before a class is usable. You should not use your instance constructors, some special private function, or any other idiom to initialize static variables. As with instance initialization, you can use the initializer syntax as an alternative to the 16 static constructor. If you simply need to allocate a static member, use the initializer syntax. When you have more plicated logic to initialize static member variables, create a static constructor. Implementing the singleton pattern in C is the most frequent use of a static constructor. Make your instance constructor private, and add an initializer: public class MySingleton { private static readonly MySingleton _theOneAndOnly = new MySingleton( )。 public static MySingleton TheOnly { get { return _theOneAndOnly。 } } private MySingleton( ) { } // remainder elided } The singleton pattern can just as easily be written this way, in case you have more plicated logic to initialize the singleton: public class MySingleton { private static readonly MySingleton _theOneAndOnly。 static MySingleton( ) { _theOneAndOnly = new MySingleton( )。 } 17 public static MySingleton TheOnly { get { return _theOneAndOnly。 } } private MySingleton( ) { } // remainder elided } As with instance initializers, the static initializers are called before any static constructors are called. And, yes, your static initializers execute before the base class39。s static constructor. The CLR calls your static constructor automatically when your type is first loaded into an application space. You can define only one static constructor, and it must not take any arguments. Because static constructors are called by the CLR, you must be careful about exceptions generated in them. If you let an exception escape a static constructor, the CLR will terminate your program. Exceptions are the most mon reason to use the static constructor instead of static initializers. If you use static initializers, you cannot catch the exceptions yourself. With a static constructor, you can (see Item 45): static MySingleton( ) { try { _theOneAndOnly = new MySingleton( )。 } catch { // Attempt recovery here. } } Static initializers and static constructors provide the cleanest, clearest way to initialize 18 static members of your class. They are easy to read and easy to get correct. They were added to the language to specifically address the difficulties involved with initializing static members in other languages.