Item 12:Perfer Variable Initializers to Assignment Statements

编译器总是在运行Constructor前，先初始化成员变量（不包括静态变量）。当有初始化语句时，你不需要为每个构造函数添加初始化语句。Equally important,the initializers are added to the complier-generated default constructor.The C# complier creates a default constructor for you types whenever you don't explicitly define any constructors.

注意：有三种情况不适合使用initializer
1.当对象或变量被初始化为null或0时

MyValueType _myclass; //initicalized to 0
MyValueType _myclass = new MyValueType(); //also 0
The default system initialization sets everything to 0(null) for you before any of your code executes.
如果你添加了额外的初始化语句（如第二种）C#编译器必需添加额外的语句去把变量重新初始化为0

2.You should use the initializer syntax only for variables that receive the same initialization in all constructor.


public class MyClass
public class MyClass
private ArrayList _col;

MyClass()
_col = new ArrayList();
}

MyClass(int size)
_col = new ArrayList();
_col = new ArrayList(size);
}
}
[b]3.如果一个成员变量初始化时很容易出错，就尽量不要使用initialization。 [/b]