Textfield in panel in frame is initially set to NOT visible; later the program sets it to visible but it doesn't show

Question

The text in txDiv0 is supposed to show up when division by 0 is attempled. It is set to NOT visible initially. The code works correctly BUT THE TEXT ONLY SHOWS WHEN I click the frame border as if to make it larger. Making the frame literally one pixel taller makes the field show up.

Code produced by GUIbuilder:

    private javax.swing.JTextField txDiv0;
...
    txDiv0 = new javax.swing.JTextField();
...
    txDiv0.setText("Division by 0 is undefined");  
...
    javax.swing.GroupLayout jPanel6Layout = new javax.swing.GroupLayout(jPanel6);
    jPanel6.setLayout(jPanel6Layout);
    jPanel6Layout.setHorizontalGroup(
      jPanel6Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
      .addGroup(javax.swing.GroupLayout.Alignment.TRAILING, jPanel6Layout.createSequentialGroup()
        .addContainerGap(javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
        .addComponent(txDiv0, javax.swing.GroupLayout.PREFERRED_SIZE, 300, javax.swing.GroupLayout.PREFERRED_SIZE)
        .addContainerGap())
    );
    jPanel6Layout.setVerticalGroup(
      jPanel6Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
      .addGroup(javax.swing.GroupLayout.Alignment.TRAILING, jPanel6Layout.createSequentialGroup()
        .addGap(0, 11, Short.MAX_VALUE)
        .addComponent(txDiv0, javax.swing.GroupLayout.PREFERRED_SIZE, 20, javax.swing.GroupLayout.PREFERRED_SIZE))
    );
...    
    pack();

And here's how I try to make it show up:

    txDiv0.setVisible(true);
    System.out.println();

(The println is there to show me that the code DID execute.)

The textfield NEVER shows up unless I barely wiggle an edge of the frame.

Answer 1

You will want to call revalidate() and then repaint() on the container that holds your txDiv0 component after changing its visibility. The reason for this is:

• revalidate() tells the component to have its layout managers re-layout the components it contains. This laying out will cascade through all the layout managers of the components that the current container holds.
• repaint() suggests to the JVM that the container may have some dirty regions that need to be repainted after components have been removed, added, or shifted around.

As an aside, I strongly urge you to lay the GUI-builder to the side when learning a GUI library, and instead try to create and modify the GUI by hand as this will give you a greater understanding of the underpinnings of the GUI library and will force you to read and study tutorials more.