not declare a static final serialVersionUID field
package doItMyself;

import javax.swing.*;

public class ClockView extends JFrame{
private JLabel tLabel = new JLabel();

ClockView(){
this.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
this.setSize(95, 45);
this.getContentPane().add(tLabel);
this.refreshTimeDisplay();
}

protected String getDigitsAsString(int i){
String str=Integer.toString(i);
if (i <10) str= "0 "+str;
return str;
}

public void refreshTimeDisplay(){
TimeStamp t= new TimeStamp();
t.fillTimes();
String display=getDigitsAsString(t.hrs)+ ": "+getDigitsAsString(t.mins)+ ": "+getDigitsAsString(t.secs);
tLabel.setText( " "+display);
tLabel.repaint();
}
}
这段程序，报出一个警告错误：The serializable class ClockView does not declare a static final serialVersionUID field of type long

[解决办法]
用工具自带的quick fix
直接在警告上面点右键就行了