Getting null pointer exception in adding frame content

Question

I got null pointer exception during content adding in JFrame in Swing.

    public static void createAndShowGUI() {
    //Create and set up the window.
    frame = new JFrame("Data Entry Application");
    //Set up the content pane.
    // frame = new JFrame();
    addComponentsToPane(frame.getContentPane());  // null pointer exception in this line
     }

 public static void addComponentsToPane(Container pane) {
    if (RIGHT_TO_LEFT) {
        pane.setComponentOrientation(ComponentOrientation.RIGHT_TO_LEFT);
    }

    Border blackline, raisedetched = null, loweredetched,
            raisedbevel = null, loweredbevel, empty, orangeline, redline, greenline, blueline;
    blackline = BorderFactory.createLineBorder(Color.black);
    orangeline = BorderFactory.createLineBorder(Color.ORANGE);
    redline = BorderFactory.createLineBorder(Color.RED);
    greenline = BorderFactory.createLineBorder(Color.GREEN);
    blueline = BorderFactory.createLineBorder(Color.blue);

    JButton button;
    pane.setLayout(new GridBagLayout());
    GridBagConstraints c = new GridBagConstraints();
    if (shouldFill) {
        //natural height, maximum width
        c.fill = GridBagConstraints.HORIZONTAL;
    }

    /* Header Section start*/
    /* Username and designation starts */
    JPanel p_username = new JPanel();
    p_username.setMinimumSize(new Dimension(140, 30));
    l_username = new JLabel(Login.login_username);
    l_designation = new JLabel("Data Entry User");

    JPanel t9 = new JPanel(new GridLayout(0, 1));
    t9.add(l_username);
    t9.add(l_designation);
    t9.setPreferredSize(new Dimension(140, 30));
    p_username.add(t9);
   c.fill = GridBagConstraints.NORTH;
    c.gridx = 0;
    c.gridy = 0;
    c.ipady = 25;
    c.insets = new Insets(0, 10, 0, 0);
    pane.add(p_username, c);
    /* Username and designation end */
  }

Suggest some idea.

Null pointer means that you are trying to use something that is null. WE can't know what that is without seeing the addComponentsToPane method. — DonyorM, Nov 03 '14 at 07:17
1) See [What is a stack trace, and how can I use it to debug my application errors?](http://stackoverflow.com/q/3988788/418556) & [What is a Null Pointer Exception, and how do I fix it?](http://stackoverflow.com/q/218384/418556) 2) Always copy/paste error and exception output! 3) For better help sooner, post an [MCVE](http://stackoverflow.com/help/mcve) (Minimal Complete Verifiable Example). — Andrew Thompson, Nov 03 '14 at 07:20

hfontanez · Answer 1 · 2014-11-03T08:17:34.927

I mocked your addComponentsToPane() method to show you what the problem is:

private static void addComponentsToPane(Container container)
{
    System.out.println("Is container null? " + container == null);
    JPanel panel = null;
    container.add(panel);
}

Calling this method results in the following output:

false
Exception in thread "main" java.lang.NullPointerException
    at java.awt.Container.addImpl(Container.java:1091)
    at java.awt.Container.add(Container.java:415)
    at FrameDemo.addComponentsToPane(FrameDemo.java:33)
    at FrameDemo.createAndShowGUI(FrameDemo.java:25)
    at FrameDemo.main(FrameDemo.java:14)

If you read the Javadoc, the getContentPane() method does not return null as you can see from the resulting output. My second line declares a JPanel but does not instantiates the object, which I then try to add to the contents pane. This is causing the NullPointerException in my case.

My conclusion: You are adding a component to the container that has not been properly instantiated. In fact, if you read the Javadoc for the Container.add(comp) method, it states that this method throws a NullPointerException if comp is null. Check all of the components you are trying to add to it and you can figure out the rest.

Getting null pointer exception in adding frame content

1 Answers1