Random Generator

[Learning Java]

Ok little bit of confusion with a Stanford University CS106a lesson on using the random generator.

Mehran Sahami uses the following code to create a private instance variable of type RamdomGenerator -- hope I said that right.

private RandomGenerator rgen = RandomGenerator.getInstance();

Anyway, for me that simply doesn't work whereas the following does:

private RandomGenerator rgen = new RandomGenerator();

Are both codes doing the same thing? Is there any reason why the other code wouldn't work for me? I mean the only difference I could think of is that I'm using a Mac whereas he was on a PC, but that shouldn't make a different right? The impression I got is that programming in Java on a Mac and programming in Java on a PC are exactly the same since they both get translated by the JVM anyway or am I mistaken?

Thanks!

[m00nchile]

Were there any errors, or did the code compile but not function as intended? From what I googled, the RandomGenerator class is part of the acm package, that isn't standard Java.

[Learning Java]

You're right it isn't standard Java. But even the ACM documentation uses that code so I'm wondering why it doesn't work for me. I get the following error:

"The method getInstance() is undifined for the type RandomGenerator"

Is it possible that there are different versions of the ACM library or something and I have one that is out of date? What's even more confusing is that the book "The Art and Science of Java" doesn't use that code either, instead it uses the "= new RandomGenerator()" code as I do :confused:

[Norm]

I just decompiled my version of the above class and found:

    public static RandomGenerator getInstance()

The class file from the acm.jar is dated 8/25/06

[JosAH]

I thought that Stanford course uses Eclipe; when you type "RandomGenerator.", Eclipse shows a list of fields and methods present in the RandomGenerator class. I don't think any confusion will be left ...

kind regards,

Jos

[Learning Java]

Ok not to worry then.

It's just that the video lecture taught one way but the book taught another way... the way the book taught works fine for me so I guess it's all good. Just wanted to know why they were different and whether it would be a problem; but I guess it shouldn't.

Thanks

[Norm]

One consideration is that the static method creates one object and returns that on future calls vs creating a new one every time you need one. Don't know how the seed is set. Does a new object always return the same series of numbers? where using the existing one would not.

[Learning Java]

I ran the following:

import acm.program.*;
import acm.util.*;

public class Test extends ConsoleProgram {

	public void run() {
		
	random.setSeed(2);	

	println (+random.nextInt());
	println (+random.nextInt());
	println (+random.nextInt());	

	}
	
	private RandomGenerator random = new RandomGenerator();

}

And yes I do get the same sequence of numbers:

-1154715079
1260042744
-423279216

each time the program is run.

[Norm]

Use a pseudo random seed by using the system's current time. That'll give you a different sequence.

[Learning Java]

Thanks mate