Why getting screen size from Toolkit yields different results depending if there´s a JFrame or not

Question

Code without frame

Code with frame

The images show the 2 different codes so I want to know why the result of the screen size in both codes varies depending on whether a JFrame was created before the call or not.

As the image shows when there's not JFrame it returns a different result than the one it returns when there's not a JFrame created yet at the moment of the call so any explanation on this phenomena would be appreciated.

Answer 1

I didn't have any issues. You might want to elaborate on your system properties

Without frame...

import java.awt.Toolkit;

public class Test {

    static double screenWidth = Toolkit.getDefaultToolkit().getScreenSize().getWidth();
    static double screenHeight = Toolkit.getDefaultToolkit().getScreenSize().getHeight();

    static double screenWidth2;
    static double screenHeight2;

    public static void main(String[] args) {
        new Test();

        System.out.println("screenWidth = " + screenWidth + " ~ " + screenWidth2);
        System.out.println("screenHeight = " + screenHeight + " ~ " + screenHeight2);
    }

    public Test() {
        screenWidth2 = Toolkit.getDefaultToolkit().getScreenSize().getWidth();
        screenHeight2 = Toolkit.getDefaultToolkit().getScreenSize().getHeight();
    }
}

Outputs...

screenWidth = 1792.0 ~ 1792.0
screenHeight = 1120.0 ~ 1120.0

With Frame

import java.awt.Toolkit;
import javax.swing.JFrame;

public class Test2 extends JFrame {

    static double screenWidth = Toolkit.getDefaultToolkit().getScreenSize().getWidth();
    static double screenHeight = Toolkit.getDefaultToolkit().getScreenSize().getHeight();

    static double screenWidth2;
    static double screenHeight2;

    public static void main(String[] args) {
        new Test2();

        System.out.println("screenWidth = " + screenWidth + " ~ " + screenWidth2);
        System.out.println("screenHeight = " + screenHeight + " ~ " + screenHeight2);
    }

    public Test2() {
        screenWidth2 = Toolkit.getDefaultToolkit().getScreenSize().getWidth();
        screenHeight2 = Toolkit.getDefaultToolkit().getScreenSize().getHeight();
    }
}

Outputs

screenWidth = 1792.0 ~ 1792.0
screenHeight = 1120.0 ~ 1120.0

System Properties

• OS: macOS Catalina, 10.15.4
• Java: 11.0.1