JFrame whose content changes as we click on the different buttons?

[Norah Jones]

I am using Java's Swing here to make a UI application. I have a created a 
JFrame, with some buttons. When I click on this button, I want a new JFrame 
with some different content at this place. However, I do not want a new JFrame 
to load here.
    One approach, I know is of setting the visbility of the second JFrame to be 
True in the actionPerformed(ActionEvent obj) method of the button in the first 
JFrame. But it again loads a new JFrame and I don't want that.
    
    public class FirstUI extends JFrame {
        JButton but1;
        public FirstUI(){
            but1= new JButton("Click here");
            add(but1);
        
        XYZ obj= new XYZ():
        but1.addActionListener(obj);
        }
        
        public class XYZ implements ActionListener{
            public void actionPerformed(ActionEvent obj1){
        
                 // WHAT TO DO HERE  
            } 
        }
    }
    
I only want a single JFrame whose content changes as we click on different 
buttons. How can I achieve that ?