Question

I am using SWING and writting with a simple Group layout

I wrote this code for the layout:

    JPanel unterPanel = new JPanel();
    GroupLayout layout = new GroupLayout(unterPanel);
    unterPanel.setLayout(layout);
    layout.setAutoCreateGaps(true);
    layout.setAutoCreateContainerGaps(true);

    layout.setHorizontalGroup(
            layout.createSequentialGroup()
            .addGroup(layout.createParallelGroup(GroupLayout.Alignment.LEADING)
                    .addComponent(header)
                    .addComponent(tableG)
                    .addGroup(layout.createSequentialGroup()
                            .addComponent(b3)
                            .addComponent(b4)
                            .addComponent(b5)
                            .addComponent(b6)
                            ))
            );
    layout.setVerticalGroup(
            layout.createSequentialGroup()
            .addGroup(layout.createParallelGroup(GroupLayout.Alignment.BASELINE)
                    .addComponent(b3)
                    .addComponent(b4)
                    .addComponent(b5)
                    .addComponent(b6)
                    )   
                    .addGroup(layout.createParallelGroup(GroupLayout.Alignment.BASELINE)
                            .addComponent(header)
                            .addComponent(tableG))
            );

    layout.linkSize(SwingConstants.HORIZONTAL, b3, b4, b5, b6);

    return unterPanel;

But when I compile the code I get:

Exception in thread "AWT-EventQueue-0" java.lang.IllegalArgumentException: Component must be non-null
    at javax.swing.GroupLayout$ComponentSpring.<init>(GroupLayout.java:2878)
    at javax.swing.GroupLayout$ComponentSpring.<init>(GroupLayout.java:2858)
    at javax.swing.GroupLayout$Group.addComponent(GroupLayout.java:1490)
    at javax.swing.GroupLayout$ParallelGroup.addComponent(GroupLayout.java:2414)
    at javax.swing.GroupLayout$ParallelGroup.addComponent(GroupLayout.java:2384)
    at javax.swing.GroupLayout$Group.addComponent(GroupLayout.java:1471)
    at javax.swing.GroupLayout$ParallelGroup.addComponent(GroupLayout.java:2406)
    at gui.guimain.Produktmaingui(guimain.java:97)
    at gui.guimain.showStart(guimain.java:306)
    at gui.guimain$1.run(guimain.java:410)
    at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:209)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:597)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:269)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:184)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:174)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:169)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:161)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)

Why?

I appreaciate your answer!!!

Answer 1

One of the components you are adding is null, in other words, one of these variables:

• header
• tableG
• b3
• b4
• b5
• b6

and the culprit is on line 97 of your class, as detailed in the stack trace.