Loading screen - JFrame setvisible from other class

Question

I want a temporary loading screen in the transition from one frame to another. In the mainframe I create the loading screen which creates the other screen (employmentframe). It only creates it, it does not show it yet.

In the employment frame I have put some loadingframe.setloadingbar() methods which call the setloadingbar method in loadingframe. This works perfect until it reaches 100. At getvalue() == 100 it should set the employmentframe visible, but instead it gives me a nullpointerexception. Which is weird because the employment-screen IS created.

The code is below -

Employmentframe:

   public EmploymentFrame(int eid, JFrame thisframe) {         
        initComponents();
        //loadCaseFileList();
        e_id = eid;
        loadCourseList();
        EmploymentFrame.thisframe = thisframe;
        LoadingFrame.setLoadingBar(1);
    }
    public static void setEmploymentFrameVisible()
    {
       thisframe.setVisible(true);
    }

The loadingframe:

private static JFrame Employmentframe;
private static int oldvalue;
private int e_id;
public LoadingFrame(int type, int eid) {
    initComponents();
    this.e_id = eid;
    if(type == 1)
    {
        Employmentframe = new EmploymentFrame(eid, Employmentframe); 
    }
}

   public static void setLoadingBar(int load)
   {
       oldvalue = LoadingBar.getValue();
       System.out.println(""+oldvalue);
       int newvalue = oldvalue+load;
       System.out.println("nv"+newvalue);
       LoadingBar.setValue(newvalue);
       if(LoadingBar.getValue() == 100)
       {
           EmploymentFrame.setEmploymentFrameVisible();
       }
   }

Thanks.

Answer 1

The stacktrace indicates that this line is throwing the NPE

thisframe.setVisible(true);

so thisframe is null.

When you create Employmentframe here

Employmentframe = new EmploymentFrame(eid, Employmentframe); 

you are passing in null as an argument to the constructor as the JFrame has not yet been initialized. In fact, the EmploymentFrame does not need to be passed an instance of itself.

---

There are a number of other issues:

• Static methods are seen as a poor design choice in any OO language
• Multiple JFrames are considered difficult to manage. Preferred alternatives are 1.) CardLayout on a single JFrame or 2.) In cases where multiple windows are required a single JFrame with a modal JDialog can be used. Also discussed here.
• Code conventions in Java indicate that variables should begin with a lowercase letter.