Bug 168314 Snippet 252 a bit confusing
Snippet 252 (the one posted on the N&N for M4) sets a line width of 1/2. Since these are both integers, it does the division first and then the cast. This sets the line style to 0.0. I assume (since the N&N says something about fractional line width) you meant 1/2f.
examples/org.eclipse.swt.snippets/src/org/eclipse/swt/snippets/Snippet252.java
public static void main(String[] args) {
		final Display display = new Display();
		final Shell shell = new Shell(display);
		
		shell.addListener(SWT.Paint, new Listener() {
			public void handleEvent(Event event) {
				GC gc = event.gc;
				
				gc.setLineAttributes(new LineAttributes(10, SWT.CAP_FLAT, SWT.JOIN_MITER, SWT.LINE_SOLID, null, 0, 10));
				gc.drawPolyline(new int[]{50, 100, 50, 20, 60, 30, 50, 45});
				
				gc.setLineAttributes(new LineAttributes(1/2f, SWT.CAP_FLAT, SWT.JOIN_MITER, SWT.LINE_DOT, null, 0, 10));
				gc.drawPolyline(new int[]{100, 100, 100, 20, 110, 30, 100, 45});
			}
		});
		
		shell.setSize(170, 170);
		shell.open();
		while (!shell.isDisposed()) {
			if (!display.readAndDispatch()) display.sleep();
		}
		display.dispose();
	}
}