To set a image in a button I did this:
JButton yourButton = new JButton("text button");
try {
yourButton.setIcon(new ImageIcon(ImageIO.read(getClass().getResourceAsStream("/images/icon-for-your-button.png"))));
} catch (IOException e3) {
// TODO Auto-generated catch block
e3.printStackTrace();
}
You must have the images inside your project like this:
In your case, the answer I think is to do this:
new ImageIcon(ImageIO.read(getClass().getResourceAsStream("/images/icon-for-your-button.png")))