Java Date Formatting DateFormat

Question

Can we use new DateFormat(); to create an object of DateFormat ?

DateFormat format = DateFormat.getDateInstance();

is used but can we use the following?

DateFormat df = new DateFormat(); 
df.getDateInstance();

Answer 1

使用SimpleDateFormat

DateFormat dateFormat = new SimpleDateFormat("yyyy.MM.dd HH:mm.ss");

Answer 2

DateFormat is an abstract class, like all abstract classes you cannot instantiate them. You can only instantiate a subclass of an abstract class provided the subclass is not abstract also. To know more about abstract classes, look at abstract classes tutorial by oracle

Answer 3

DateFormat is an abstract class with protected constructor.You can use SimpleDateFormat like this. This statement won't even compile.

  DateFormat d=new DateFormat();

Answer 4

The constructor is defined as

protected DateFormat()

which means you cannot call it like that. Neither can you do something like:

DateFormat df = DateFormat;

It does not provide any aliasing mechanism to avoid typing it. So you will have to always to do:

DateFormat df = DateFormat.getDateInstance();

Or you can use a subclass as @Verhagen has pointed out.

It is also an abstract class, but one way you could do it is use an anonymous constructor:

    java.text.DateFormat df = new java.text.DateFormat(){
        @Override
        public Date parse(String source, ParsePosition pos) {
            // TODO Auto-generated method stub
            return null;
        }
        @Override
        public StringBuffer format(Date date, StringBuffer toAppendTo,
                FieldPosition fieldPosition) {
            // TODO Auto-generated method stub
            return null;
        }
    };

but in this case you have to define what those methods do.

Answer 5

You can use SimpleDateFormat which is an implementation and not an abstract class as stated in @Verhagen answer, but be bareful with it, most of the times you got to use it in a ThreadLocal to avoid those problems.

It has some pretty bad side effects when used in a multi threaded environment.

With Java 8 the recomended is to use the new Date API

final DateTimeFormatter formatter =  
      DateTimeFormatter.ofPattern(dateTimeFormatPattern);  
   final String nowString = formatter.format(now8);