C#引用变量使用说明

Question

我不是程序员,我想了解以下代码:

A a=new A();
B a=new B();

a=b;      
c=null;

b=c; 

如果变量只持有引用,那么'a'到底是否为空？

Answer 1

假设所有对象a,b,c都来自同一个类,a则不会null.它将b在赋值之前保存引用的值c.

让我们假设你有以下课程

class Test
{
    public int Value { get; set; }
}

然后尝试:

Test a = new Test();
a.Value = 10;
Test b = new Test();
b.Value = 20;
Console.WriteLine("Value of a before assignment: " + a.Value);
a = b;
Console.WriteLine("Value of a after assignment: " + a.Value);
Test c = null;
b = c;
Console.WriteLine("Value of a after doing (b = c) :" + a.Value);

输出将是:

Value of a before assignment: 10
Value of a after assignment: 20
Value of a after doing (b = c) :20

Answer 2

你需要在脑海中离婚两个概念; 的参考和对象.该引用本质上是托管堆上对象的地址.所以:

A a = new A(); // new object A created, reference a assigned that address
B b = new B(); // new object B created, reference b assigned that address
a = b; // we'll assume that is legal; the value of "b", i.e. the address of B
       // from the previous step, is assigned to a
c = null; // c is now a null reference
b = c; // b is now a null reference

这不会影响"a"或"A"."a"仍然保留我们创建的B的地址.

所以不,"a"最终不是空的.