c# - what does this mean? (about class and instance) -

using system;  class program {     static void main()     {         haha haha1;     } }  class haha {     int a;     int b;      public haha(int a, int b)     {         this.a = a;         this.b = b;     } } 

i know if want make instance, should write code such as:

haha haha1 = new haha(1,2); 

but when write just

haha haha1; 

there's no compile error.

what haha haha1; mean? isn't wrong code?

it not wrong code. variable declaration.

haha haha1; 

simply declares variable named haha1 has type haha. variable not assigned value.

when instantiate object new keyword:

haha1 = new haha(); 

the variable refers object created