在java中使用currentTimeMillis方法 计时但是返回的时间老是一个1640395283397之类的数

long startMillis1=0,endMillis1,useTime1,tongji1=0 ,zhuanhua1;
    int changerzhi1=0;
    long startMillis=0,endMillis,useTime,tongji=0,zhuanhua;
    int changerzhi=0;
    if(e.getSource()==button1)
    {
         button3.setText(text1.getText()); 
    }
    else if(e.getSource()==button2)
    {
        button5.setText(text2.getText()); 
    }
    else if(e.getSource()==button3)
    {
        //开始计时
        startMillis1 = System.currentTimeMillis(); 
    }
    if(e.getSource()==button5)
    {
        //开始计时
        startMillis = System.currentTimeMillis();
     }
    if(e.getSource()==button4) {
         
         String zhi1=text3.getText();
         changerzhi1=Integer.valueOf(zhi1);
     if(changerzhi1>num1) 
         lable3.setText("大了");
     else if(changerzhi1<num1) 
         lable3.setText("小了");
     else 
         lable3.setText("good，good");
     endMillis1 = System.currentTimeMillis();
     useTime1 = (endMillis1-startMillis1)/1000;
     tongji1+=useTime1; 
     if(changerzhi1==num1)
     {
         lable5.setText("恭喜"+text1.getText()+"率先完成累计时间"+tongji1);
         System.out.println(tongji1+"asdas "+tongji);
         System.out.println(endMillis1);
     }
    }     
     if(e.getSource()==button6) {
         String zhi1=text4.getText();
         changerzhi=Integer.valueOf(zhi1);
     if(changerzhi>num2) 
         lable4.setText("大了");
     else if(changerzhi<num2) 
         lable4.setText("小了");
     else 
         lable4.setText("good，good");
     endMillis = System.currentTimeMillis();
     useTime = (endMillis - startMillis)/1000;
     
     tongji+=useTime;
     if(changerzhi==num2)
     {
         lable5.setText("恭喜"+text2.getText()+"率先完成累计时间"+tongji);
         System.out.println(tongji1+"asdas "+tongji);
         System.out.println(endMillis);
     }
}
     

我就是想实现点击button3开始统计时间 到我点击button4的时候完成操作在结束计时 然后在把每次计时的时间累加到最后 一起输出 但是输出来的时间总是
1640395283397之类的数 痛苦死了 求告知 万分感谢

你想要2021-12-25 10:00这样的时间？

currenttime是当前时间毫秒值