Consider the following class declaration:

public class Thing

$\{$

private int x;

private int y;

private static int z $=0$;

public Thing$()$

$\{$

x$=$z;

y$=$z;

$\}$

static void putThing$($int a$)$

$\{$

z$=$a;

$\}$

$\}$

Assume a program containing the class declaration defines three Thing objects with the

following statements:

Thing one $=$ new Thing$()$;

Thing two $=$ new Thing$()$;

Thing three $=$ new Thing$()$;

How many separate instances of the variable $x$ exist?