package tsinghuaip;import javax.swing.UIManager;import java.awt.*;public class IPAssignApp {    boolean packFrame = false;    //Construct the application    public IPAssignApp() {        IPAssignFrm frame = new IPAssignFrm();        //Validate frames that have preset sizes        //Pack frames that have useful preferred size info, e.g. from their layout        if (packFrame) {            frame.pack();        }        else {            frame.validate();        }        //Center the window        Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();        Dimension frameSize = frame.getSize();        if (frameSize.height > screenSize.height) {            frameSize.height = screenSize.height;        }        if (frameSize.width > screenSize.width) {            frameSize.width = screenSize.width;        }        frame.setLocation((screenSize.width - frameSize.width) / 2, (screenSize.height - frameSize.height) / 2);        frame.setVisible(true);        frame.setResizable(false);    }    //Main method    public static void main(String[] args) {        try {            UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());        }        catch(Exception e) {            e.printStackTrace();        }        new IPAssignApp();    }}