I am using java on debian 5

java version "1.6.0_20"
Java(TM) SE Runtime Environment (build 1.6.0_20-b02)
Java HotSpot(TM) Client VM (build 16.3-b01, mixed mode, sharing)

Why is there a difference between the following

Case 1:

import java.util.*;

Case 2:

import java.util.*;
import java.util.Arrays;
import java.util.List;

Why doesnt the first case cover the second case?

The code only compiles when I import Arrays and List explicitly.

Code:

import java.util.*;
import java.util.Arrays;
import java.util.List;
public class Test { public static void main (String[] args) { List<Integer> i = new ArrayList(Arrays.asList(1,2,3,4,5,6,7,8,9,10)); List<Integer> j = new ArrayList(); ListIterator<Integer> n = i.listIterator(i.size()); while(n.hasPrevious()) { j.add(n.previous()); } println(j); } static void println(Object o) { System.out.println(o); } static void print(Object o) { System.out.print(o); }
}

The error I get when I comment out the 2nd and 3rd import statements are:

nattyp@debian:~/dev/java$ javac Test.java
Test.java:7: cannot find symbol
symbol : method asList(int,int,int,int,int,int,int,int,int,int)
location: class Arrays List<Integer> i = new ArrayList(Arrays.asList(1,2,3,4,5,6,7,8,9,10)); ^
Note: Test.java uses unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.
1 error
nattyp@debian:~/dev/java$

0

4 Answers

I have just compile it and it compiles fine without the implicit import, probably you're seeing a stale cache or something of your IDE.

Have you tried compiling from the command line?

I have the exact same version:

Probably you're thinking the warning is an error.

UPDATE

It looks like you have a Arrays.class file in the directory where you're trying to compile ( probably created before ). That's why the explicit import solves the problem. Try copying your source code to a clean new directory and try again. You'll see there is no error this time. Or, clean up your working directory and remove the Arrays.class

4

The difference between

import java.util.*;

and

import java.util.*;
import java.util.List;
import java.util.Arrays;

becomes apparent when the code refers to some other List or Arrays (for example, in the same package, or also imported generally). In the first case, the compiler will assume that the Arrays declared in the same package is the one to use, in the latter, since it is declared specifically, the more specific java.util.Arrays will be used.

Case 1 should have worked. I don't see anything wrong. There may be some other problems. I would suggest a clean build.

0

Take a look at this forum . Theres a discussion on how using wildcards can lead to conflicts if you add new classes to the packages and if there are two classes with the same name in different packages where only one of them will be imported.

Update

It gives that warning because your the line should actually be

List<Integer> i = new ArrayList<Integer>(Arrays.asList(0,1,2,3,4,5,6,7,8,9,10));
List<Integer> j = new ArrayList<Integer>();

You need to specify the type for array list or the compiler will give that warning because it cannot identify that you are using the list in a type safe way.

3

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