import javax.swing.*;
import java.awt.*;
public class MyClass {
public static void main(String args[]) {
JFrame myFrame = new JFrame();
myFrame.setSize(new Dimension(500, 500));
myFrame.setMinimumSize(new Dimension(300, 300));
myFrame.setMaximumSize(new Dimension(800, 800));
myFrame.setVisible(true);
myFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}
}