for loop

[zulqernain]

i am reading core java 2 vol 1 by horstmann & cornell .in this book ,in the chapter of event handling .he has written method

public void paintComponent(Graphics g)
{
	super.paintComponent(g);
	Graphics2D g2=(Graphics2D) g;
	
	for(Line2D l: lines)
	{
		g2.draw(l);
	}
		
}

private ArrayList<Line2D> lines;

i have not understood what does this 'for' loop mean.it is giving me error too.
how to fix it

also in the declaration
private ArrayList<Line2D> lines;

<Line2D> gives me error