There are no options to create a fixed (non-resizeable) window in the GUI editor.
i.e. if I want to make a fixed window, after initComponents(); I have to type:
        this.getFrame().setResizable(false);
This could easily be a tick box in the Properties window.

Testcase:
Create a desktop application using the Basic Application style in the New Java Desktop Application Wizard. It gives a 
basic skeleton on which you can develop. 
If the project is called Test you will have a skeletion of TestApp.java TestAboutBox.java and TestView.java. 

TestView.java is the file which contains the UI, the Inspector pane shows a structure like this:

FormTestView
I
I--------[FrameView]
I
I-------mainPanel[JPabel]
I
I-------menuBar[JMenu bar]
I
I------statusPanel[JPanel]

Click on any of the components and notice that there are no properties in the Properties Window to make the 
setResizable property false.