import javax.swing.JFrame;
import java.awt.Color;
import java.awt.Insets;

public class GameTestMain {
JFrame frame1;

GameTestMain(){
frame1 = new JFrame("ゲームテスト");
frame1.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame1.setBackground(Color.WHITE);
frame1.setResizable(false);

frame1.setVisible(true);
Insets insets = frame1.getInsets();
frame1.setSize(600 + insets.left + insets.right,
400 + insets.top + insets.bottom);
frame1.setLocationRelativeTo(null);
}

public static void main(String[] args) {
GameTestMain gtm = new GameTestMain();
}