Random numbers with Math random in Java

Question

For generating random numbers  I ve used the formula    int  Math random     max    min  The formula I find on Google always seem to be    int  Math random      max - min    min   Which one s right  As far as I know  I ve never gotten a number that was out of my range with my formula

User · Answer

Math random   generates a number between 0  inclusive  and 1  exclusive    So  int  Math random     max  ranges from 0 to max-1 inclusive   Then  int  Math random     max    min ranges from min to max   min - 1  which is not what you want   Google s formula is correct

User · Answer

Your formula generates numbers between min and min   max   The one Google found generates numbers between min and max   Google wins

User · Answer

Math random        Returns a double value with a positive sign  greater than or equal to   0 0 and less than 1 0    Now it depends on what you want to accomplish  When you want to have Numbers from 1 to 100 for example you just have to add    int  Math random   100    So 100 is the range of values  When you want to change the start of the range to 20 to 120 you have to add  20 at the end   So the formula is    int  Math random   range    min   And you can always calculate the range with max-min  thats why Google gives you that formula

User · Answer

if min 10 and max 100    int  Math random     max    min           gives a result between 10 and 110  while   int  Math random      max - min    min    gives a result between 10 and 100  so they are very different formulas  What s important here is clarity  so whatever you do  make sure the code makes it clear what is being generated    PS  the first makes more sense if you change the variable  max  to be called  range

User · Answer

Google is right  -   Google s formula creates numbers between  min and max Your formula creates numbers between  min and  min max

User · Answer

If min   5  and max   10  and Math random   returns  almost  1 0  the generated number will be  almost  15  which is clearly more than the chosen max   Relatedly  this is why every random number API should let you specify min and max explicitly  You shouldn t have to write error-prone maths that are tangential to your problem domain

User · Answer

A better approach is   int x   rand nextInt max - min   1    min    Your formula generates numbers between min and min   max   Random random   new Random 1234567   int min   5  int max   20  while  true        int x    int  Math random     max    min      System out println x       if  x  lt  min    x  gt   max    break               Result   10 16 13 21    Oops     See it online here  ideone

User · Answer

The first one generates numbers in the wrong range  while the second one is correct   To show that the first one is incorrect  let s say min is 10 and max is 20  In other words  the result is expected to be greater than or equal to ten  and strictly less than twenty  If Math random   returns 0 75  the result of the first formula is 25  which is outside the range

User · Answer

There s a small problem with the formula that you found on Google  It should be   int  Math random      max - min   1    min  not  int  Math random      max - min    min       max - min   1 is the range in which random numbers can be generated

User · Answer

Yours  Lowest possible is min  highest possible is max min-1  Google  Lowest possible is min  highest possible is max-1

User · Answer

int i    int   10  Math random   11     this will give you random number between 10 to 20   the key here is   a   Math random   b   a starting num  10  and ending num is max number  20  - a  10     1  11   Enjoy

[java] Random numbers with Math.random() in Java

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