java获取屏幕宽度

package com.test;
import javax.swing.*;
import java.awt.Toolkit;
import java.awt.Dimension;
public class Test extends JFrame {
 public Test(String name){
  super(name);
  this.setSize(300,200);
  Dimension dem=Toolkit.getDefaultToolkit().getScreenSize();
  int sHeight=dem.height;
  int sWidth=dem.width;
  System.out.println(sHeight+"====="+sWidth);
  int fHeight=this.getHeight();
  int fWidth=this.getWidth();
  this.setLocation((sWidth-fWidth)/2, (sHeight-fHeight)/2);
  System.out.println(sHeight);
  this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

 }
 public static void main(String[] args) {
	 Test frame=new Test("myFrame");
  frame.setVisible(true);
 }
}