With Netbeans I've succeded center a jpanel with fixed size, within an other jpanel. Now I can't repeat it - only copy it.

How did I do? (or should I do to center x and y a jpanel with fixed size in another jpanel).

The result differs in code:

Working - search for .addContainerGap( and see next not working:

        javax.swing.GroupLayout center3Layout = new javax.swing.GroupLayout(center3);
        center3.setLayout(center3Layout);
        center3Layout.setHorizontalGroup(
            center3Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGap(0, 1064, Short.MAX_VALUE)
            .addGroup(center3Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                .addGroup(center3Layout.createSequentialGroup()
                    .addContainerGap(30, Short.MAX_VALUE)
                    .addComponent(mainPanel3, javax.swing.GroupLayout.PREFERRED_SIZE, 
javax.swing.GroupLayout.DEFAULT_SIZE, 
javax.swing.GroupLayout.PREFERRED_SIZE)
                    .addContainerGap(30, Short.MAX_VALUE)))
        );
        center3Layout.setVerticalGroup(
            center3Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGap(0, 650, Short.MAX_VALUE)
            .addGroup(center3Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                .addGroup(center3Layout.createSequentialGroup()
                    .addContainerGap(23, Short.MAX_VALUE)
                    .addComponent(mainPanel3, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                    .addContainerGap(23, Short.MAX_VALUE)))
        );

Not working - search for .addGap compared with above working.

    javax.swing.GroupLayout center2Layout = new javax.swing.GroupLayout(center2);
    center2.setLayout(center2Layout);
    center2Layout.setHorizontalGroup(
        center2Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGap(0, 1073, Short.MAX_VALUE)
        .addGroup(center2Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(center2Layout.createSequentialGroup()
                .addGap(0, 34, Short.MAX_VALUE)
                .addComponent(mainPanel2, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addGap(0, 35, Short.MAX_VALUE)))
    );
    center2Layout.setVerticalGroup(
        center2Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGap(0, 654, Short.MAX_VALUE)
        .addGroup(center2Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(center2Layout.createSequentialGroup()
                .addGap(0, 25, Short.MAX_VALUE)
                .addComponent(mainPanel2, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addGap(0, 25, Short.MAX_VALUE)))
    );

I've looked side by side in properties etc - please help! :)