What's the difference between import java.util

问题:

I just want to output current and I wrote

import java.util.*;

at beginning, and

System.out.println(new Date());

in the main part.

But what I got was something like this:

Date@124bbbf

When I change the import to import java.util.Date; the code works perfectly, why?

====================================

The problem was, OK, my source file was "Date.java", that's the cause.

Well, it is all my fault, I confused everybody around ;P

And thanks to everyone below. It's really NICE OF YOU ;)

回答1:

You probably have some other "Date" class imported somewhere (or you have a Date class in you package, which does not need to be imported). With "import java.util.*" you are using the "other" Date. In this case it's best to explicitly specify java.util.Date in the code.

Or better, try to avoid naming your classes "Date".

回答2:

The toString() implementation of java.util.Date does not depend on the way the class is imported. It always returns a nice formatted date.

The toString() you see comes from another class.

Specific import have precedence over wildcard imports.

in this case

import other.Date
import java.util.*

new Date();

refers to other.Date and not java.util.Date.

The odd thing is that

import other.*
import java.util.*

Should give you a compiler error stating that the reference to Date is ambiguous because both other.Date and java.util.Date matches.

回答3:

import java.util.*;

imports everything within java.util including the Date class.

import java.util.Date;

just imports the Date class.

Doing either of these could not make any difference.

回答4:

Your program should work exactly the same with either import java.util.*; or import java.util.Date;. There has to be something else you did in between.

回答5:

but what I got is something like this: Date@124bbbf  
while I change the import to: import java.util.Date;  
the code works perfectly, why? 

What do you mean by "works perfectly"? The output of printing a Date object is the same no matter whether you imported java.util.* or java.util.Date. The output that you get when printing objects is the representation of the object by the toString() method of the corresponding class.