Question

I register to a cardPanel object 3 JPanel.

JPanel cardPanel = new JPanel(new CardLayout());

cardPanel.add(viewPerf, "Performances");
cardPanel.add(viewFaults, "Faults");
cardPanel.add(viewGraph, "Throughput Graph");

I would obtain exactly one JPanel.how can I do this operation?

Answer 1

To show a particular component in a CardLayout, use the CardLayout#show(String) method, passing the name you gave the component when you added it:

((CardLayout)cardPanel.getLayout()).show("Throughput Graph");

Alternatively, you can save the layout when you create it:

CardLayout cardPanelLayout = new CardLayout();
cardPanel.setLayout(cardPanelLayout);
...
cardPanelLayout.show("Throughput Graph");

Edit: To get a reference to the currently visible component, I believe you can do this:

Component visibleComp = null;
for (Component comp : cardPanel.getComponents()) {
  if (comp.isVisible()) {
    visibleComp = comp;
    break;
  }
}