explain this ...please

[aman hindustani]

hello to all...please explain this..why y,z is printing zero..


public class justSimple
{
public static void main(String[] args)
{
System.out.println("Hello World!");
int x =0;
int y =0;
int z = 0;
y = y++;
z = y;
System.out.println("the value of x is "+x);
System.out.println("the value of y is "+y); // 0
System.out.println("the value of z is "+z); // 0
}
}