int x = 0;
int y = 0;
int direction = 0;
void setup()
{

frameRate(240);
size(500,500);  
}

void draw()
{
background(100,100,100);
rect(x,y,25,25);

if (x == 475)
{
x  = 0;
}

if (x == - 25)
{
x = 475;
}

if (direction == 0)
{
x++;
}

if (direction == 1)
{
x--;
}

if (y == 475)
{
y  = 0;
}

if (y == - 25)
{
y = 475;
}

if (direction == 2)
{
y--;
}

if (direction == 3)
{
y++;
}

}

void keyPressed()
{
if (keyCode == RIGHT) 
{
direction = 0;
}

if (keyCode == LEFT) 
{
direction = 1;

}

if (keyCode == UP) 
{
direction = 2;

}

if (keyCode == DOWN)
{
direction = 3;
}

}