How do I generate random integers within a specific range in Java? -

i trying generate random intvalue java, in specific range.

for example:

my range 5-10, meaning 5 smallest possible value , 10 biggest. other number in between these numbers possible value, too.

in java, there method random() in math class, returns double value between 0.0 , 1.0. in class random there method nextint(int n), returns random int value in range of 0 (inclusive) , n (exclusive). couldn't find method, returns random integer value between 2 numbers.

i have tried following things, still have problems: (minimum , maximum smallest , biggest numbers).

solution 1:

randomnum = minimum + (int)(math.random() * maximum);  

problem:

randomnum can bigger maximum.

solution 2:

random rn = new random(); int n = maximum - minimum + 1; int = rn.nextint() % n; randomnum =  minimum + i; 

problem:

randomnum can smaller minimum.

how solve these problems?

i have tried browsing through archive , found:

• expand random range 1–5 1–7
• generate random numbers uniformly on entire range

but couldn't solve problem.

in java 1.7 or later, standard way follows:

import java.util.concurrent.threadlocalrandom;  // nextint exclusive of top value, // add 1 make inclusive int randomnum = threadlocalrandom.current().nextint(min, max + 1); 

see the relevant javadoc. approach has advantage of not needing explicitly initialize java.util.random instance, can source of confusion , error if used inappropriately.

however, conversely there no way explicitly set seed can difficult reproduce results in situations useful such testing or saving game states or similar. in situations, pre-java 1.7 technique shown below can used.

before java 1.7, standard way follows:

import java.util.random;  /**  * returns pseudo-random number between min , max, inclusive.  * difference between min , max can @  * <code>integer.max_value - 1</code>.  *  * @param min minimum value  * @param max maximum value.  must greater min.  * @return integer between min , max, inclusive.  * @see java.util.random#nextint(int)  */ public static int randint(int min, int max) {      // note: (intentionally) not run written folks     // copy-pasting have think how initialize     // random instance.  initialization of random instance outside     // main scope of question, decent options have     // field initialized once , re-used needed or     // use threadlocalrandom (if using @ least java 1.7).     random rand;      // nextint exclusive of top value,     // add 1 make inclusive     int randomnum = rand.nextint((max - min) + 1) + min;      return randomnum; } 

see the relevant javadoc. in practice, java.util.random class preferable java.lang.math.random().

in particular, there no need reinvent random integer generation wheel when there straightforward api within standard library accomplish task.