What do these symbols mean?

What do these symbols mean?

 Stmt_init (); var_dump ($ stmt); $ mysqli-> close ();

The result is:
Object (mysqli_stmt) #2 (0 ){}

Where #2 means 0, and curly brackets

Reply to discussion (solution)

Object (mysqli_stmt) #2 (0 ){}
Indicates
Object (mysqli_stmt) this is a mysqli_stmt object
#2 is the second in the mysqli Object series ($ mysqli is the first)
(0) the number of members is 0 (only list attributes)
{} So it is an empty set

Is it an object series, can it be understood as an array? If it is an array, can print_r () be used to print it out? I just learned it, but sometimes it cannot be reflected. sorry.

Different data structures of objects and arrays
Output mode object $ m-> name array $ m ['name']