Playername

String name = "User";

public void started()
{
    for (int i=0; i<3; i++)
    {
        String nm = Greenfoot.ask("Enter name (no more than 10 characcters long)");
        if (nm == null || "".equals(nm) || nm.length() > 10) continue;
        name = nm;
    }
}

String name;
Actor namePlate;

public Player(String nm)
{
    name = nm;
}
protected void addedToWorld(World world)
{
    namePlate = new NamePlate();
    namePlate.setPosition();
}

public void act()
{
    // put at end and before any 'return;' statements
    namePlate.setPosition();
}

// still in Player class
private class NamePlate extends Actor
{
    public NamePlate()
    {
        GreenfootImage img = new GreenfootImage(name, 17, Color.BLACK, Color.CYAN);
        setImage(img);
    }
    
    public void setPosition()
    {
        if (Player.this.getWorld() == null)
        {
            if (getWorld() != null) getWorld().removeObject(this);
            return;
        }
        if (getWorld() == null) Player.this.getWorld().addObject(this, 0, 0);
        setLocation(Player.this.getX(), Player.this.getY()-Player.this.getImage().getHeight()/2-10);
    }
}