The validate() and doLayout() methods

Question

In the first mini-program I made, what is the purpose of the validate() method? I read that it is to force the container into using the new layout manager for the components added. My first question is just: why don't I have to call the validate() method to ensure that the new layout manager is being used?
import javax.swing.*;
import java.awt.*;
public class ShowLayout extends JFrame
    public ShowLayout()
        setTitle("MyFrame");
        setSize(200,200);
        setVisible(true);
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setLayout(new FlowLayout());
        add(new JButton("Accept"));
        add(new JButton("Cancel"));
        setLayout(new GridLayout());
        //validate(); // why is this needed? It seems to work without it
    public static void main(String[] args)
        ShowLayout showLayout = new ShowLayout();
}According to my understanding of what I've read about the doLayout() method, it is used to force the container to re-layout the components given the new properties of the layout manager.
Also, what is the purpose of the doLayout() method? Similarly, my second question is: why don't I have to call the doLayout() method to ensure that the new properties have taken effect?
import javax.swing.*;
import java.awt.*;
public class ShowLayout extends JFrame
    public ShowLayout()
        setTitle("MyFrame");
        setSize(200,200);
        setVisible(true);
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setLayout(new FlowLayout());
        add(new JButton("Accept"));
        add(new JButton("Cancel"));
        setSize(100,100);
        //doLayout(); // why is this needed? It seems to work without it      
    public static void main(String[] args)
        ShowLayout showLayout = new ShowLayout();
}Are both of these methods called implicitly? Is the explicit calling of these methods only mandatory with an older JVM?
Sorry if my questions seem stupid but any input would be greatly appreciated!

Answer 1

You appear to have some funcamental misconceptions regarding the action of revalidate() and doLayout(). Have you read the API for those methods?
I recommend you to the Swing tutorials linked form the topic listing page for this forum. By going through the tutorials you can learn things systematically.
The usual programming idiom is to add all components to the GUI hierarchy before its top level window is setVisible(true), not after. Also, all Swing components should be constructed and modified on the EDT and only on the EDT. Not on the main thread.
db