java 随意控制控件的位置

package chat1;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class chat1{
    public chat1(){
        JFrame jf = new JFrame();
        jf.setLayout(null);
        jf.setSize(280,560);
        jf.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        JButton logn = new JButton("logn");
        JButton out = new JButton("out");
        logn.setBounds(170,480,80,30);    //  参数分别为坐标，控件的规格
        out.setBounds(15,480,80,30);
        jf.add(logn);
        jf.add(out);
        jf.setVisible(true);
    }

    public static void main(String[] args){ 

        chat1 frame = new chat1();

    }

}