FAQ: Learn Java: Loops - While We're Here

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This community-built FAQ covers the “While We’re Here” exercise from the lesson “Learn Java: Loops”.

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[danniboi82]

Directions asks to reset dieRoll with a new random value between 1 and 6 , inside the loop
which I understand as

while(dieRoll != 5) {
     dieRoll = randomGenerator.nextInt(6) + 1;
}

What is the correct way to reset dieRoll inside the while loop??? I cannot get past this stage… Please help

[pranavshridhar]

Why not use

((int)Math.random() * 6) + 1;

of the Math library? That’s what I was taught in class and it works in my IDE just fine.

[fulalsayab]

you have to reset the random number between 1 and 6; yours is between 1 and 7.

[eefkeburg]

First you have to create a first instance, before you let it repeat, I guess. This works:

// Creating a random number generator
Random randomGenerator = new Random();

// Generate a number between 1 and 6
int dieRoll = randomGenerator.nextInt(6) + 1;

// Repeat while roll isn't 5
while (dieRoll != 5) {
  
  System.out.println(dieRoll);
		dieRoll = randomGenerator.nextInt(6) + 1;

[piyushbag]

Can someone please explain, why +1 is used with randomGenerator.nextInt(6)

[stetim94]

If you see code you don’t understand, the best thing to teach yourself is to break the problem down in small steps.

so in this case, what would randomGenerator.nextInt(6) generate? Looking at documentation/tutorial we see the following example (source):

so randomGenerator.nextInt(6) would generate 0 till (and including) 5. But we want 1 till (and including) 6.

Well, the +1 just explained itself

Teaching yourself to think this way as early as possible is a good skill to have

[object6503193471]

Yeah this makes total sense. The only way to get around the “+1” would be a random number generator that didn’t include “zero”. Like instead of using “int” we would need a data type that only includes the the positive integers (whole numbers) 1, 2, 3, etc. I want to use the term “natural numbers” here, it’s been a long time since I did any number theory so that might be incorrect. Hopefully the description is clear.

[object6503193471]

This is exactly how I wrote my code and it is working just fine.

[object6503193471]

// Repeat while roll isn't 5
    while (dieRoll != 5) {
      System.out.println(dieRoll);
      dieRoll = randomGenerator.nextInt(6) + 1;

Here is my solution to both questions of step 2/8. The first and third line are part of question one and the middle line is the answer to the second question. Eleven numbers/die rolls were printed to the console before the while loop terminated (evaluated to false).

[sidneybeatty]

Hello,

I wanted to know if someone could explain why we have to reset “dieRoll” inside the while loop if “dieRoll” has been initialized with a value of “randomGenerator.nextInt(6) + 1”? I understand the lesson said that the value of “dieRoll” would never change if its not reset inside the “while loop”, but why?

// Importing the Random library
import java.util.Random;

class LuckyFive {

public static void main(String args) {

// Creating a random number generator
Random randomGenerator = new Random();

// Generate a number between 1 and 6
int dieRoll = randomGenerator.nextInt(6) + 1;

// Repeat while roll isn't 5
while (dieRoll != 5) {
  
  System.out.println(dieRoll);
	  dieRoll = randomGenerator.nextInt(6) + 1;

}

[stetim94]

you need to keep rolling the die until we have rolled 5. This is achieved by using a loop.

[sidneybeatty]

Okay I understand that the “while” statement will run until we roll 5 hence the “!= 5”. I guess specifically I’m trying to understand the lesson’s statement:

" Do NOT run your code yet — you will get an infinite loop here because the value of dieRoll is never changed. "

(Correct me if I’m wrong please):
I think I now understand why the value of “dieRoll” would not change and why we would get an infinite loop if the code is ran without a reset of “dieRoll”.

//Here “dieRoll” is initialized and is equal to 6. Therefore, if you were to run the " while (dieRoll != 5) " without the reset of " dieRoll " inside the “while loop” it would be a infinite loop. Because "dieRoll remains at the value 6.

int dieRoll = randomGenerator.nextInt(6) + 1;

Is this correct?

[stetim94]

@sidkid52

I think I now understand why the value of “dieRoll” would not change and why we would get an infinite loop if the code is ran without a reset of “dieRoll”.

its not a reset, we update an existing variable.

The rest seems accurate.

[bonnio]

// Importing the Random library
import java.util.Random;

class LuckyFive {
  
  public static void main(String[] args) {
    
    // Creating a random number generator
    Random randomGenerator = new Random();
    
    // Generate a number between 1 and 6
    int dieRoll = randomGenerator.nextInt(6) + 1;

    // Repeat while roll isn't 5
    while (dieRoll != 5) {
      System.out.println(dieRoll);
      randomGenerator.nextInt(6);
    }
    
  }
  
}

Everytime I try to run this code, the website crashes, but if I leave System.out.println(dieRoll); out, it works just fine. Can someone tell me what I did wrong?

[stetim94]

@bonnio

Everytime I try to run this code, the website crashes

this very likely means you have an infinite loop.

You never update the dieRoll variable, so you might generate a new random number, but you don’t do anything with this newly generated number

[psmilliorn]

Here’s a hint on what’s going on. I downloaded the code and ran it. This was the output.

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I had to manually shut it off after this filled my console.

[hampusl]

Could someone explain to me why the order of the code is like it is:

// Importing the Random library
import java.util.Random;

class LuckyFive {

public static void main(String args) {

// Creating a random number generator
Random randomGenerator = new Random();

// Generate a number between 1 and 6
int dieRoll = randomGenerator.nextInt(6) + 1;

// Repeat while roll isn't 5
while (dieRoll != 5) {
  
  System.out.println(dieRoll);
		dieRoll = randomGenerator.nextInt(6) + 1;

}

}

}

and why do we have the “int dieRoll = randomGenerator.nextInt(6) + 1;” followed by the same line without “int” instead → dieRoll = randomGenerator.nextInt(6) + 1; lastly?

If that makes sense

[stetim94]

we only need to specify the data type when we declare the variable, when we assign a new value to existing variable (like you do in the while loop), the data type is already known.

[hampusl]

Ah right, that was brought up in the earlier lessons. Thanks!