some simple question?

[jperson]

i want to know what's

System.out (it's class out in package System ?)
---------
JOptionPane.showMessageDialog(null,"message"); (what's first argument null)
i want an example to use this method but first argument not null?
---------

[PhHein]

System (Java 2 Platform SE 5.0)
JOptionPane (Java 2 Platform SE 5.0)

[jperson]

thank u for help PhHein but
i can't understand showMessage Dialog()

i make this simple code

public class Main {

public static void main(String[] args) {
JFrame frame = new JFrame();
frame.setVisible(true);
frame.setSize(400, 500);
JOptionPane.showMessageDialog(null, "test");



}
}

i can't see any changes if my argument is null or frame
i want some help to understand this argument please ??

[PhHein]

Click the JFrame while the JOptionPane is visible, once with the null parameter and once with frame as the first parameter.

[jperson]

i see JOptionPane inside the JFrame when i use JOptionPane.showMessageDialog(frame, "test");

i think that's the difference