C#基础 继承和实例化
2021-06-21 01:06
标签：write 结果 click closed console soscw read public 构造函数 有代码如下，问输出的是多少： 结果：x=1;y=0; 刚开始有点不理解，觉得输出是x=1;y=-1;然后反编译看了下IL代码，然而。。还是没看出来，IL代码如下： 最后打断点，找到了原因 原因分析： B b = new B(); 执行顺序： 1、int x = 1;int y;给x赋值1，给y赋值默认为0（int类型） 2、public B()，然后关键点来了 3、public A()，执行A里面的PrintFields();但是A里面的这个方法是个虚方法，会调用B里面重写的方法 4、public override void PrintFields()这个是B里面的然后Console.WriteLine("x={0},y={1}", x, y);结果当然就是x=1;y=0; 5、然后才回到了B的public B()，接着给y赋值y = -1;这个时候y才变了，如果这个时候打印y的值才是-1，这个时候B的实例化就完成了 关键点：实例化类的时候，会先执行继承的父类的构造函数，如果父类构造函数含有虚方法又会回调子类的重写方法，之后才回到初始类的构造函数 C#基础 继承和实例化 标签：write 结果 click closed console soscw read public 构造函数 原文地址：https://www.cnblogs.com/zhyue93/p/ctor.htmlclass Program
{
static void Main(string[] args)
{
B b = new B();
Console.ReadKey();
}
class A
{
public A()
{
PrintFields();
}
public virtual void PrintFields() { }
}
class B : A
{
int x = 1;
int y;
public B()
{
y = -1;
}
public override void PrintFields()
{
Console.WriteLine("x={0},y={1}", x, y);
}
}
}
.class private auto ansi beforefieldinit Program
extends [mscorlib]System.Object
{
.method public hidebysig specialname rtspecialname instance void .ctor() cil managed
{
.maxstack 8
L_0000: ldarg.0
L_0001: call instance void [mscorlib]System.Object::.ctor()
L_0006: nop
L_0007: ret
}
.method private hidebysig static void Main(string[] args) cil managed
{
.entrypoint
.maxstack 1
.locals init (
[0] class ConsoleApplication1.Program/B b)
L_0000: nop
L_0001: newobj instance void ConsoleApplication1.Program/B::.ctor()
L_0006: stloc.0
L_0007: call valuetype [mscorlib]System.ConsoleKeyInfo [mscorlib]System.Console::ReadKey()
L_000c: pop
L_000d: ret
}
.class auto ansi nested private beforefieldinit A
extends [mscorlib]System.Object
{
.method public hidebysig specialname rtspecialname instance void .ctor() cil managed
{
.maxstack 8
L_0000: ldarg.0
L_0001: call instance void [mscorlib]System.Object::.ctor()
L_0006: nop
L_0007: nop
L_0008: ldarg.0
L_0009: callvirt instance void ConsoleApplication1.Program/A::PrintFields()
L_000e: nop
L_000f: ret
}
.method public hidebysig newslot virtual instance void PrintFields() cil managed
{
.maxstack 8
L_0000: nop
L_0001: ret
}
}
.class auto ansi nested private beforefieldinit B
extends ConsoleApplication1.Program/A
{
.method public hidebysig specialname rtspecialname instance void .ctor() cil managed
{
.maxstack 8
L_0000: ldarg.0
L_0001: ldc.i4.1
L_0002: stfld int32 ConsoleApplication1.Program/B::x
L_0007: ldarg.0
L_0008: call instance void ConsoleApplication1.Program/A::.ctor()
L_000d: nop
L_000e: nop
L_000f: ldarg.0
L_0010: ldc.i4.m1
L_0011: stfld int32 ConsoleApplication1.Program/B::y
L_0016: ret
}
.method public hidebysig virtual instance void PrintFields() cil managed
{
.maxstack 8
L_0000: nop
L_0001: ldstr "x={0},y={1}"
L_0006: ldarg.0
L_0007: ldfld int32 ConsoleApplication1.Program/B::x
L_000c: box int32
L_0011: ldarg.0
L_0012: ldfld int32 ConsoleApplication1.Program/B::y
L_0017: box int32
L_001c: call void [mscorlib]System.Console::WriteLine(string, object, object)
L_0021: nop
L_0022: ret
}
.field private int32 x
.field private int32 y
}
}
