Date date = new Date();

        DateFormat dateformat = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");

        String StringDate = String.valueOf(dateformat.format(date));

String stringDate= "2018-02-01 11:11:11";

        DateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");

        try{

            Date date = dateFormat.parse(stringDate);

            System.out.println(date);

        }

        catch(ParseException e)

        {

            e.printStackTrace();

        }

        int intNum = 12345;

        String stringNum = String.valueOf(intNum);

        double doubleNum1 = Double.parseDouble(stringNum);//Double.parseDouble返回的是基本数据类型double

        DecimalFormat df = new DecimalFormat("#.00");

        String dfString = df.format(doubleNum1);

        System.out.println(dfString);//在jdk1.5之后的可以自由相加。

        double doubleNum = 1.545;

        DecimalFormat df = new DecimalFormat("0");

        int intNum = Integer.parseInt(df.format(doubleNum));//这是四舍五入，非四舍五入直接强转。