JFrame very small

I'm following a tutorial and made a JFrame, but it's very tiny. Iv'e searched for this problem on this site, but nothing has helped. Does anybody know the problem? I did it exactly like the tutorial, and it worked for him! I'll post a picture of it also.

Here is the code:

    package net.trails.std;
import java.applet.Applet;
import java.awt.Dimension;
import java.awt.Image;

import javax.swing.JFrame;

public class Core extends Applet implements Runnable {

    private static final long serialVersionUID = 1L;
    private static JFrame frame;

    public static double dY = 0, dX = 0;
    public static final int res = 1;
    public static int dir = 0;

    public static boolean moving = false;
    public static boolean run = false;

    private Image screen;

    public static Dimension screenSize = new Dimension(700, 560);
    public static Dimension pixel = new Dimension(screenSize.width, screenSize.height);
    public static Dimension size;

    public static String name = "Trails";

    public Core(){



    }

    public static void main(String[] args) {

        Core core = new Core();
        frame = new JFrame();
        frame.add(core);
        size = new Dimension(frame.getWidth(), frame.getHeight());
        frame.setSize(700, 560);
        frame.setTitle(name);
        frame.setResizable(false);
        frame.setLocationRelativeTo(null);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.pack();
        frame.setVisible(true);
        core.start();

    }


    public void run() {



    }

}