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Thread: Can a for loop work with random number?

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    Default Can a for loop work with random number?

    Hi all,

    I need to write code to make a kangaroo object jump a random number of times between 1 & 6 times. I have an instance variable declared of type random, called ranNumber. I also have a getter method for this variable. Just so you know the message jump takes no argument. I think i need to use a for loop for this so the code I have come up with so far is:

     public void kangarooJump(Kangaroo aKangaroo)
         {
            ranNumber.nextInt(7);
            for (int jumps = 0; jumps < getRanNumber(); jump ++)
            {
               aKangaroo.jump();
            }
     
         }

    The problems I am having are when i try to compile I get an error message "<operator cannot be applied to int, java.util.Random. I understand why this error is coming up but I cant tink of a way to resolve it.

    Is it even possible to do what I want with a for loop or is there another way to do it?
    it needs to be kept as simple as possible as im only in the early stages of learning Java.

    Hope someone can help. Thankyou in advance to anyone who takes the time to read this.


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    Administrator copeg's Avatar
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    Default Re: Can a for loop work with random number?

    You should draw the random prior to initiating the loop. I don't know what getRanNumber() actually does because the code isn't posted for it, but based upon this it doesn't look like its needed

            int max  = ranNumber.nextInt(6) + 1;//add one because you want to jump between 1 and 6
            for (int jumps = 1; jumps < max; jump ++)//start loop at 1 and go for max times
            {
               aKangaroo.jump();
            }

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    humdinger (January 19th, 2010)

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    Java kindergarten chronoz13's Avatar
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    Default Re: Can a for loop work with random number?

    use Math.random.... thi is the class that usually use to generate random numbers

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    humdinger (January 19th, 2010)

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    Default Re: Can a for loop work with random number?

    There are two ways to generate random numbers:
    Math.random (eh, basic but functional) and the Random class. Math.random() generates a double on the interval [0,1) (includes 0, doesn't include 1).

    Random can be used to generate a variety of different data types right away.

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    humdinger (January 19th, 2010)

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    Default Re: Can a for loop work with random number?

    As a side note: behind the scenes, Math.random uses a static instance of Random and its nextDouble function to generate a random number. IMO that 'middle man' design makes getting a random number much easier because you can do so from a static context.

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    Default Re: Can a for loop work with random number?

    so whats the better between the two?
    confusing... because i got used to the .random() of Math.. do they have similar purpose?

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    humdinger (January 19th, 2010)

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    Default Re: Can a for loop work with random number?

    Quote Originally Posted by chronoz13 View Post
    so whats the better between the two?
    I don't think there is a right or wrong answer to this question...it depends upon context. Math.random is static, and so can be easily accessed across classes and this alone may make it more often used. Random must be instantiated, but provides easy methods to retrieve primitive types. One major advantage to Random is that it can be extended - say for example to create methods to return random objects in addition to primitives - making it advantageous in that sense.

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    Default Re: Can a for loop work with random number?

     public void kangarooJump(Kangaroo aKangaroo)
         {
            ranNumber.nextInt(7);
            for (int jumps = 0; jumps < getRanNumber(); jump ++)
            {
               aKangaroo.jump();
            }
     
         }

    If you're doing Math.random(), then one of your problems is that you're trying to set a for loop to run for a fraction of a time. You might be setting it to
     for(int jumps = 0; jumps < 0.1; jumps++)
    You can't have a loop do a fraction of an iteration. You should probably rather use
     Random randGenerator = new Random(); 
    int number = randGenerator(7);
    for(int jumps = 0; jumps<number; jumps++)

    That should fix your problem. Hope that helped!

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    humdinger (January 19th, 2010)

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