Math random explanation

Question

This is a pretty simple Java  though probably applicable to all programming  question      Math random   returns a number between zero and one    If I want to return an integer between zero and hundred  I would do    int  Math floor Math random     101    Between one and hundred  I would do    int  Math ceil Math random     100    But what if I wanted to get a number between three and five  Will it be like following statement     int  Math random     5   3   I know about nextInt   in java lang util Random  But I want to learn how to do this with Math random

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Here s a method which receives boundaries and returns a random integer  It is slightly more advanced  completely universal   boundaries can be both positive and negative  and minimum maximum boundaries can come in any order   int myRand int i from  int i to      return  int  Math random      Math abs i from - i to    1     Math min i from  i to       In general  it finds the absolute distance between the borders  gets relevant random value  and then shifts the answer based on the bottom border

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The Random class of Java located in the java util package will serve your purpose better  It has some nextInt   methods that return an integer  The one taking an int argument will generate a number between 0 and that int  the latter not inclusive

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int randomWithRange int min  int max       int range    max - min    1          return  int  Math random     range    min      Output of randomWithRange 2  5  10 times   5 2 3 3 2 4 4 4 5 4   The bounds are inclusive  ie  2 5   and min must be less than max in the above example   EDIT  If someone was going to try and be stupid and reverse min and max  you could change the code to   int randomWithRange int min  int max       int range   Math abs max - min    1          return  int  Math random     range     min  lt   max   min   max       EDIT2  For your question about doubles  it s just   double randomWithRange double min  double max       double range    max - min           return  Math random     range    min      And again if you want to idiot-proof it it s just   double randomWithRange double min  double max       double range   Math abs max - min           return  Math random     range     min  lt   max   min   max

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To generate a number between 10 to 20 inclusive  you can use java util Random   int myNumber   new Random   nextInt 11    10

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If you want to generate a number from 0 to 100  then your code would look like this    int  Math random     101     To generate a number from 10 to 20     int  Math random     11   10     In the general case    int  Math random       upperbound - lowerbound    1    lowerbound      where lowerbound is inclusive and upperbound exclusive    The inclusion or exclusion of upperbound depends on your choice  Let s say range    upperbound - lowerbound    1 then upperbound is inclusive  but if range    upperbound - lowerbound  then upperbound is exclusive   Example  If I want an integer between 3-5  then if range is  5-3  1 then 5 is inclusive  but if range is just  5-3  then 5 is exclusive

[java] Math.random() explanation

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