Java JFrame .setSize(x, y) not working?

1. Create a custom component, extending from JPanel, override its getPreferredSize method to return the size of the window you would like.
2. Either add this to your frame or set it as the frame’s content pane.
3. Call pack on the frame

Updated with example

On my PC, the Frame size = java.awt.Dimension[width=216,height=238]

import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.FontMetrics;
import java.awt.Graphics;
import java.awt.Graphics2D;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class TestFrameSize01 {

    public static void main(String[] args) {
        new TestFrameSize01();
    }

    public TestFrameSize01() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                }

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setLayout(new BorderLayout());
                frame.add(new TestPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);

                System.out.println("Frame size = " + frame.getSize());
            }
        });
    }

    public class TestPane extends JPanel {

        public TestPane() {
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(200, 200);
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics2D g2d = (Graphics2D) g.create();
            String text = getWidth() + "x" + getHeight();
            FontMetrics fm = g2d.getFontMetrics();
            int x = (getWidth() - fm.stringWidth(text)) / 2;
            int y = ((getHeight() - fm.getHeight()) / 2) + fm.getAscent();
            g2d.drawString(text, x, y);
            g2d.dispose();
        }
    }    
}