e1001. overriding the default action of a jtextcomponent.txt

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The default action in a text component keymap receives all typed characters that are not handled in any inputmap or keymap. This example demonstrates how to wrap the default action of a text component with a custom default action. 
    JTextArea component = new JTextArea();
    Action defAction = findDefaultAction(component);
    
    // Install the overriding default action
    component.getKeymap().setDefaultAction(new MyDefaultAction(defAction));
    
    public class MyDefaultAction extends AbstractAction {
        Action defAction;
        public MyDefaultAction(Action a) {
            super("My Default Action");
            defAction = a;
        }
        public void actionPerformed(ActionEvent e) {
            // Perform customizations here
            // This example upper cases all typed characters
            if (e.getActionCommand() != null) {
                String command = e.getActionCommand();
                if (command != null) {
                    command = command.toUpperCase();
                }
                e = new ActionEvent(e.getSource(), e.getID(), command, e.getModifiers());
            }
    
            // Now call the installed default action
            if (defAction != null) {
                defAction.actionPerformed(e);
            }
        }
    }
    
    public Action findDefaultAction(JTextComponent c) {
        // Look for default action
        // Check local keymap
        Keymap kmap = c.getKeymap();
        if (kmap.getDefaultAction() != null) {
            return kmap.getDefaultAction();
        }
    
        // Check parent keymaps
        kmap = kmap.getResolveParent();
        while (kmap != null) {
            if (kmap.getDefaultAction() != null) {
                return kmap.getDefaultAction();
            }
            kmap = kmap.getResolveParent();
        }
        return null;
    }

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