public class MyImageIcon extends JFrame {

private static final long serialVersionUID = 1L;

public MyImageIcon() {

Container container = getContentPane();// 创建一个标签

JLabel jl = new JLabel("这是一个JFrame窗体", JLabel.CENTER);

// 获取图片URL

URL url = MyImageIcon.class.getResource("imageButton.jpg");

Icon icon = new ImageIcon(url); // 实例化Icon

jl.setIcon(icon); // 为标签设置图片

// 设置文字居中

jl.setHorizontalAlignment(SwingConstants.CENTER);

jl.setOpaque(true);

container.add(jl);

setSize(250, 100);

setVisible(true);

setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);

}

public static void main(String[] args) {

new MyImageIcon();

}

}

出错的提示

Exception in thread "main" java.lang.NullPointerException

at javax.swing.ImageIcon.<init>(Unknown Source)

at MyImageIcon.<init>(MyImageIcon.java:21)

at MyImageIcon.main(MyImageIcon.java:34)

图片放在src下了.    

21行对应的是

Icon icon = new ImageIcon(url); 

34行    

new MyImageIcon();