512212021 Random Number Generation in Java - DZone Java DZone. 4 & Wuserstoginnimy — Q (/search) REFCARDZ (/refcardz) RESEARCH (/research) WEBINARS (/webinars) ZONES v DZone (/) > Java Zone (|java-idk-development-tutorials-tools-news) > Random Number Generation in Java Random Number Generation in Java (Jusers/2520536/john-1.html) by John Thompson (/users/2520536/john-1.html) &MVB - Dec. 26, 17 « Java Zone (/java-jdk-development-tutorials-tools-news) * Tutorial © Like (31) g@Comment (5) YY Save W Tweet [Report] The Total Cost of Ownership for Cloud Databases What are all the costs that you need to account for when evaluating commitment to a cloud database? Learn how to evaluate the total ¢ database in this free guide. Download for Free » ® Cockroach Labs While developing applications, we often need to generate random numbers. Java provides support for generating random numbers primarily through the java.lang.Math (https: //docs.oracle.com /javase/8 /docs/api/java/lang/Math.html) and java.util, Random (https://docs.oracle.com /javase/8 /docs/api/java/util/Random.html) classes, In this post, I will discuss different ways to generate random numbers based on different types of requirements. Random Numbers Using the Math Class Java provides the Math class in the java.util package to generate random numbers. The Math class contains the static Math.random() method to generate random numbers of the double type. The random() method returns a double value with a positive sign, greater than or equal to 0.0 and less than 1.0. When you call Math.random(), under the hood, a java.util.Random pseudorandom-number generator object is created and used. hitps dzone. convatilesirandom-number-generatonin-java 19512272021 Ronom Number Generation ava - DZone Jove @RZal MGs random method with or widoutuperssinig bavamet@s. (/arch) reveondds paransteite tal PEL BEG" REBEARE RUA ETS SURES the given parameters, The code to use the Math.random() method: 1 public static double getRandomNunber(){ 2 double x = Math.random() 5 3 return x; ay The getRandomNumber() method uses the Math.random() method to return a positive double value that is greater than or equal to 0,0 and less than 1.0. The output of running the code is: 1 Double between 0.0 and 1.0: SimpleRandonNumber = 0.21753313144345698 Random Numbers Within a Given Range For generating random numbers between a given a range, you need to specify the range. A standard expression for accomplishing this is: 1 (Math.random() * ((max + min) + 1)) + min Letus break this expression into steps: 1. First, multiply the magnitude of the range of values you want to cover by the result that Math.random() produces. Math.random() * ( max - min ) returnsa value in the range [0, max - min] where max is excluded. For example, if you want [5,10], you need to cover integer values so you can use Math.random()*5. This would return a value in the range [0,5], where 5 is not included. 2. Next, shift this range up to the range that you are targeting, You do this by adding hitps dzone. convatilesirandom-number-generaton-in-java 29512212021 Random Number Generation in Java - DZone Java pane: one. & (isersioginnimy Q (/search) (Math.random() * ( max - min )) + min REFCARDZ (/refcardz) RESEARCH (/research) WEBINARS (webinars) ZONES » But this still does not include the maximum value. * To get the max value included, you need to add 1 to your range parameter (max - min). This will return a random double within the specified range. double x = (Math.random()*((max-min)+1))-+min; There are different ways of implementing the above expression, Let us look ata couple of them. Random Double Within a Given Range By default, the Math.random() method returns a random number of the type double whenever it is called, The code to generate a random double value between a specified range is: 1 public static double getRandonboubleBetweenRange(double min, double max){ 2 double x = (Math.random()*((max-min)+1))+min; 3 return x; 4) You can call the preceding method from the main method by passing the arguments like this. 1 System.out.printIn("Double between 5.@ and 10.2: RandomDoubleNunber = "+getRandonDoubleBetwe, The outputs this, 1 System.out.println("Double between 5.0 and 10.00: RandonDoubleNunber = +getRandonDoubleBetwe: Random Integer Within a Given Range The code to generate a random integer value between a specified range is this. 1 public static double getRandomIntegerBetweenRange(double min, double max){ hitps dzone. convatilesirandom-number-generaton-in-java 39512212021 & Wserstoginnimy) Q (/search) REFCARDZ (/refcardz) RESEARCH (/research) WEBINARS (/webinars) ZONES v The preceding getRandomIntegerBetweenRange() method produces a random integer between the given range. As Math.random() method generates random numbers of double type, you need to truncate the decimal part and cast it to int in order to get the integer random number. You can call this method from the main method by passing the arguments as follows: 1 System.out.printIn("Integer between 2 and 6: RandomIntegerNumber = “+getRandonIntegerBetweenk The output is this. 1 Integer between 2 and 6: RandonIntegerNunber = 5 Note: You can pass a range of negative values to generate a random negative number within the range. Random Number Generation Using the Random Class You can use the java.util.Random class to generate random numbers of different types, such as int, float, double, long, and boolean. To generate random numbers, first, create an instance of the Random class and then call one of the random value generator methods, such as nextInt(), nextDouble(), or nextLong(). The nextint() method of Random accepts a bound integer and returns a random integer from 0 (inclusive) to the specified bound (exclusive). The code to use the nextInt() method is this. 1 public static int generateRandontnt(int upperRange){ 2 Random random = new Random(); 3 return random.nextInt (upperRange) ; hitps dzone. convaticlesirandom-number-generaton-in-java 49512212021 Random Number Generation in Java - DZone Java DZone. 0 & (isersioginimy _Q (/search) REFCARDZ (/refcardz) RESEARCH (/research) WEBINARS (/webinars) ZONES ~ The code to use the nextInt() method to generate an integer within a range is: 1 public static int generateRandontntIntRange(int min, int max) { 2 Random r = new Random(); 3 return renextInt((ax - min) + 1) + min; ay The nextFloat() and nextDouble() methods allow generating float and double values between 0.0 and 1.0. The code to use both the methods is: 1 public static double generateRandonbouble(){ 2 Random random = new Random(); 3 return randon.nextDouble} 4) 5 6 public static float generateRandonFloat(){ 7 Random randon = new Random); 8 return random.nextFloat(); 9} Random Number Generation Features in Java 8 Java 8 (https://dzone.com/articles/java-8-concepts-fp-lambda-expressions-and- streams) introduced a new method, ints(), in the java.util. Random class. The ints() method returns an unlimited stream of pseudorandom int values. You can limit the random numbers between a specified range by providing the minimum and the maximum values. The code to use the Random ints() method to generate random integer values within a specified range is this. 1 public static int getRandomNumberInts(int min, int max){ 2 Random random = new Random(); 3 return random. ints (min, (maxe1)).findFirst().getastnt(); 4) hitps dzone. convatilesirandom-number-generaton-in-java 59512212021 Random Number Generation in Java - DZone Java @ @DZone. o & (isersitoginimy Q (/search) REPRARBZ ARSE URRRERREN LEO SORBATE AWSEES! EKA Integers between the mir (inclusive} and max (exclusivej As inisG-uretiud produces air iniSueany die code calls the findFirst() method that returns an Optionalint object that describes the first element of this stream. The code then calls the getAsInt()method to return the int value in Optionallnt. The code to use the Random .ints() method to generate a stream of specified random integer values is: public static void getStreamOfRandomInts(int num) { 1 2 Random random = new Random(); 3 random. ints (num). sorted(). forEach(System.ou 4 intl) 5 The code to call the preceding method is: System.out.printn("Random int stream: RandomIntStreanofSize = "); 2 RandonDeno. getStreanofRandomints(5); The output of the preceding code is: 1 Random int stream: RandonIntStreamofSize = 2. -1861317227 3 -1205557317 4 453883217 5 762357682 6 1725970934 The code to use the Random.ints() method to generate a stream of a specified number of random integer values between a range is: 1 public static void getStreanOfRandomintswithRange(int num, int min, int max) { 2 Random randon = new Random(); 3 randon.ints(num,min, max).sorted().for€ach(System.out: :println) ; ay hitps dzone. convatilesirandom-number-generaton-in-java cr512212021 Random Number Generation in Java - DZone Java ARCO NR idreceding method is: & Wserstoginnimy) Q (/search) REF CAR eln Oe Foe RaNGoR WAC SEPCaN of MECN ARD SMe Linge NSoninestreanoFSizernRang. 2. RandonDeno..getStreanOFRandonIntshithRange(5, 0,10); The output of the preceding code is: 1 Random int stream of specified size in range: RandomIntStreanofSizeInRange = 22 3 4 5 6 In addition to ints(), some other frequently used methods that Java 8 introduced to the Random class — which can return a sequential stream of random numbers — are: + LongStream longs() * DoubleStream doubles() Summary The java.util. Random class implements what is generally called a linear congruential generator (https://en.wikipedia.org/wiki/Linear_congruential_generator) (LCG). Itis designed to be fast but does not meet requirements for real-time use, such as use in unique session ID generation on a web server, scientific experiments, cryptography, or lotteries and sweepstakes where a monetary stake is involved. For such scenarios, there are other alternatives, which I will cover in a later post. For the impatient readers, you can have a look at the SecureRandom (https: //docs.oracle.com/javase/8 /docs /api/java/security /SecureRandom html) class and Xorshift random number generators (https: //wwwjavamex.com/tutorials/random_numbers/xorshift shtml#.Wg7SaEqWwbl v). Also, an interesting resource is random.org (https://random.org/), a true random. number service that generates randomness via atmospheric noise. hitp.tdzone.convartclesirandom-number-generation-injava 78512212021 Random Number Generation in Java - DZone Java DZone. 0 & (isersioginimy Q (/search) REFCARDZ (/refcardz) RESEARCH (/research) WEBINARS (/webinars) ZONES v Topics: JAVA, RANDOM NUMBERS, JAVALANG.MATH, JAVA.UTIL.RANDOM, TUTORIAL Published at DZone with permission of John Thompson, DZone MVB. See the original article here, (https://springframework.guru/random-number-generation-in-java/) Opinions expressed by DZone contributors are their own. 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