package liulei;import javax.swing.UIManager;import java.awt.*;public class yuangong {  boolean packFrame = false;  //Construct the application  public yuangong() {    Frame2 frame = new Frame2();    //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);  }  //Main method  public static void main(String[] args) {    try {      UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());    }    catch(Exception e) {      e.printStackTrace();    }    new yuangong();  }}