disposing onto a bufferstrats but .show wont show graphics

Question

So I've just learnt about BS and dispose from what I've been told the dispose is basically disposing the graphical objects that I've written so far onto the BS, and then with the bs.show It should be displaying the colour blue on my background however it's not.

Best regards

My code as it stands is;

         BufferStrategy bs = getBufferStrategy();
        if(bs==null){
            createBufferStrategy(3);
            return;
        }

        Graphics g = bs.getDrawGraphics(); 
        g.setColor(Color.BLUE);
        g.fillRect(0,0,getWidth(), getHeight()); 
        g.dispose(); 
        bs.show(); 
        }