How to control a panel nested in JtabbedPane ?

Question

I have a MainJtabbedPane which contains multiple JtabbedPanes each of the JtabbedPanes contain multiple pannels.

I need to be able to access the pannels from the MainJtabbedPane.

JTabbedPane[] components = (JTabbedPane[]) Main_Tabbed_Panel.getComponents();

for(int i=0; i<components.length;i++)
{
for(int j=0;j<components[i].getTabCount();j++)
{
.....
}
}

Giving an error java.awt.component cannot be cast to javax.swing.JtabbedPane

Answer 1

JTabbedPane[] components = (JTabbedPane[]) Main_Tabbed_Panel.getComponents();

The getComponents() method returns an array of Components. You can't just cast them to a JTabbedPane even if you know all the components will be an instance of JTabbedPane. You need to structure your code something like:

for(Component component: main_Tabbed_Panel.getComponents())
{
    if (component instanceof JTabbedPane)
    {
        JTabbedPane tabbePane = (JTabbedPane)component;

        // do something with the tabbed pane
    }
}

Also, follow Java naming conventions. Variable name should NOT start with an upper case character. (ie. "Main_Tabbed_Pane does not follow conventions).

Answer 2

Switch the (JTabbedPane[]) cast to (Component[]). If you hover over the getComponents() method, you'll see it returns Component[]

If you want to convert that Component[] to JTabbedPane[], you need to do it manually, as well as making sure to check for mistakes along the way (making sure its a JTabbedPane before adding it to a JTabbedPane[])

JTabbedPane[] panes = convertComponents(getComponents());

private JTabbedPane[] convertComponents(Component[] comps) {
    JTabbedPane[] panes = comps.length > 0? new JTabbedPane[comps.length] : null;
    if(panes != null)
        for(int i = 0; i < panes.length; i++) {
            if(comps[i] instanceof JTabbedPane)
            panes[i] = (JTabbedPane) comps[i];
        }
    return panes;
}

Although this isn't the most efficient, because for each item that isn't a JTabbedPane in getComponents(), there will be an empty spot in your JTabbedPane array, which you then have to clean up.

JTabbedPane[] panes = comps.length > 0? new JTabbedPane[comps.length] : null;

This first checks if the Component[] passed through the parameters has 1 or more spaces. If not, dont bother initializing with an instance.

if(panes != null)

Since theres a chance panes could initialize as null, we much check before trying to use it

for(int i = 0; i < panes.length-1; i++) {

Since Component[] comps and JTabbedPane[] panes have the same size, it doesn't matter which length you use, as long as we know how many times to loop.

if(comps[i] instanceof JTabbedPane)

This is what I meant where I said "if the component isn't a JTabbedPane, you will have a null space in your array". This will check if it's a JTabbedPane before putting it in our panes array. If not, it's ignored completely, and that space in panes is left as null

After the loop is complete, it will return the array we just made.