Date.format(Date) vs. Date.format(Object)

Question

I found java.text.DateFormat has 2 methods to format date. One is taking Date parameter, the other taking Object parameter. I checked DateFormat source code and it seems that they call different internal methods.

My question is which method (way) I should use to format Date? WAY 1 vs WAY 2

Here is my code:

 Object dateObject; // This is an instance of java.util.Date

 DateFormat df = this.createDateFormat();

 String formatted1 = df.format ( (Date) dateObject );  // WAY 1

 String formatted2 = df.format ( dateObject );  // WAY 2 -- Calling different internal method.

NOTE that, For WAY 1, I cast dateObject to java.util.Date

Anyone has any ideas? Thanks.

Answer 1

It doesn't matter. The format(Object) is part of the base Format interface; DateFormat also provides a format(Date) for clarity.

Ultimately, the format(Object) version calls DateFormat.format(Object, StringBuffer, FieldPosition) which, from the source, will attempt the following, in order:

• If object is a Date, cast to Date and perform same conversion as format(Date).
• If object is a Number, construct a new Date(((Number)object).longValue()) then format that.
• Otherwise, throw an IllegalArgumentException.

That first point makes format(Object) identical to format(Date) when the object is a Date.

In your case, since date is an Object, I would simply use format(Object) because it is less verbose, and format(Object) will do the cast for you.

Answer 2

Your WAY1 method is from DateFormat class, WAY2 method is from Format class (ancestor of DateFormat). I think both ways calls format method from DateFormat so both ways are equivalent.