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How to Create the Most Basic Java Window

On Microsoft Windows, a lot of Java programming involves creating command line applications. But I like to get to opening a graphic window as quickly as possible. This is no problem because it's actually very easy to create a basic JFrame window.

The methods required to create a windows are in the javax.swing library. The swing library includes classes to make buttons, check boxes, list boxes, menus, varius types of panes, tabs, tables, text areas, and many more graphical user interface components.

In the example code shown below, after I import the javax.swing library, I create the applications class named JFrameDemo which contains the main function, the starting point for every java application.

import javax.swing.*;

public class JFrameDemo
{

   public static void main(String s[])
   {
      JFrame frame = new JFrame("JFrame Demo");
      frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
      frame.setSize(300,300);
      frame.setLocationRelativeTo(null);
      frame.setVisible(true);
   }
}

In the main function I create a new JFrame object named frame. Next I call the setDefaultCloseOperation method, which takes a constant that defines what happens when you click the frames close button:

DO_NOTHING_ON_CLOSEIgnore the click
HIDE_ON_CLOSEHide the frame, but keep the application running
DISPOSE_ON_CLOSEDispose of the frame, but keep the application running
EXIT_ON_CLOSEExit the application

Next I call the setSize method, passing it the width and height (in pixels) of the window. The resulting size will include the title bar, menu, border, ect.

Next I call the setLocationRelativeTo method, which sets the location of the window relative to a specified component. If the specified component is not currently visible, or the value passed is null, the window is centered on the screen.

Next I call the setVisible method. setVisible(true) makes the window visible. setVisible(false) makes the windows invisible.

Jframe Demo

On the Microsoft Windows operating system, Java applications are often run from DOS batch files, but when the batch file closes, so does the Java application. You can prevent this by using the DOS pause command, which will keep the command window open until the user hits a key. But in the case of a graphical window, you may want to get rid of the command window while leaving the java application window open. You can accomplish this by, instad of calling java to execute the application, use the DOS start command to call javaw to execute the application.

start javaw JFrameDemo2

The javaw command requires no associated command window to remain running, and the DOS start command closes the command window immediately after it has executed the batch file's last command.

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