Question on java.util.Random

[Bob Beerbower]

I'm trying to use the Random class for generating random numbers. If I use the following import statement

import java.util.Random;  

the code complies. However if I use,

import java.util.*;  

I get an error message

can not find symbol method nextInt()

This is the code I'm running;

import java.util.Random;
import javax.swing.*;
 

        public class Test {
 
                private static Random rn = new Random();
 
                private Test()
                {
                }
 
                public static int rand(int lo, int hi)
                {
                        int n = hi - lo + 1;
                        int i = rn.nextInt() % n;
                        if (i < 0)
                                i = -i;
                        return lo + i;
                }
                
        public static void main(String[] args) {

JOptionPane.showMessageDialog(null,
"Random = " + rand(1,10)
+  "\n Random  = " + rand(1,10)
+  "\n Random  = " + rand(1,10)
+  "\n Random  = " + rand(1,10)
+  "\n Random  = " + rand(1,10)
+  "\n Random  = " + rand(1,10)
+  "\n\n Random  = " + rand(1,100)
+  "\n Random  = " + rand(1,100)
+  "\n Random  = " + rand(1,100)
+  "\n Random  = " + rand(1,100)
+  "\n\n Random  = " + rand(98,100));
        }

}  

My understanding is that util.Random is a subset of util.*. If so why won't my code using util.* compile. The sample I copied off the web used util.*, but I couldn't get that to compile either.

[Jim Yingst]

My guess is that you've got another class called Random lying around in the current directory. (Or in some other directory which is on your classpath.) When you explicitly name java.util.Random it finds that class first, but when you say java.util.* it finds the other class first. This is one reason why it's often recommended to prefer specific imports to wildcards. Also it's advisable to avoid using class names which duplicate standaard library class names, such as Random.

Incidentally that "rand" method is needlessly complex, and has some subtle bugs which are probably not suitable for discussion in the beginner forum. (See Effective Java p. 145-6 for an explanation.) There's an overload of the nextInt() method, nextInt(int), which can be used here to make a rand() method which is both simpler and more effective.

[Bob Beerbower]

Thanks. I thought I got rid of that other Random class, I'll check again. I'll look at the rand mathod as well.
[ January 01, 2006: Message edited by: Bob Beerbower ]