Java Swing 绝对格局管理方法，null布局

import java.awt.Container;import java.awt.Dimension;import java.awt.Rectangle;import java.awt.Toolkit;import javax.swing.JButton;import javax.swing.JCheckBox;import javax.swing.JComboBox;import javax.swing.JFrame;import javax.swing.JPasswordField;import javax.swing.JTextField;public class Log extends JFrame {	public static void main(String[] args) {		Log log = new Log();	}	private JButton btLog;	private JTextField tfUser;	private JPasswordField tfPwd;	private JCheckBox pwdKeep;	private JComboBox adminType;	public Log() {		super("固定资产管理系统");		super.setSize(380, 292);		super.setVisible(true);		super.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);		centered(this);		btLog = new JButton("登     录");		btLog.setBounds(new Rectangle(93, 220, 180, 30));//参数分别是坐标x，y，宽，高		this.setLayout(null);//设置布局管理器为空		this.add(btLog);		tfUser = new JTextField();		tfUser.setBounds(new Rectangle(73, 115, 220, 25));		this.add(tfUser);		tfPwd = new JPasswordField();		tfPwd.setBounds(new Rectangle(73, 150, 220, 25));		this.add(tfPwd);		pwdKeep = new JCheckBox("记住密码");		pwdKeep.setBounds(new Rectangle(68, 185, 110, 25));		this.add(pwdKeep);		adminType = new JComboBox(new String[] { "普通职员", "管理员", "高级管理员" });		adminType.setBounds(new Rectangle(183, 185, 100, 25));		this.add(adminType);	}//布局居中方法	public void centered(Container container) {		Toolkit toolkit = Toolkit.getDefaultToolkit();		Dimension screenSize = toolkit.getScreenSize();		int w = container.getWidth();		int h = container.getHeight();		container.setBounds((screenSize.width - w) / 2,				(screenSize.height - h) / 2, w, h);	}}