在下面这个程序中System.out.println(frame.WIDTH); System.out.println(frame.HEIGHT);两句系统为什么会输出1和2.这个不明白?

import javax.swing.*;

import java.awt.*;

public class CenterFrame {

public static void main(String args[]){

JFrame frame =new JFrame("Test centerFrame");

frame.setSize(400,300);

frame.setVisible(true);

frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

//Get the dimension of the screen

Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();

int screenWidth = screenSize.width;

int screenHeight = screenSize.height;

//Get the dimension of the frame

Dimension frameSize = frame.getSize();

int x = (screenWidth - frameSize.width)/2;

int y = (screenHeight-frameSize.height)/2;

System.out.println(frame.WIDTH);

System.out.println(frame.HEIGHT);

frame.setLocation(x, y);

}

}

能对上面的红色字体说得再详细一点吗?是系统的一个常量,把这个说得再明白一点,可以吗?