(window.webpackJsonp=window.webpackJsonp||[]).push([[1651],{2059:function(t,a,s){"use strict";s.r(a);var n=s(31),e=Object(n.a)({},(function(){var t=this,a=t.$createElement,s=t._self._c||a;return s("ContentSlotsDistributor",{attrs:{"slot-key":t.$parent.slotKey}},[s("h1",{attrs:{id:"random-number-generation"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#random-number-generation"}},[t._v("#")]),t._v(" Random Number Generation")]),t._v(" "),s("h2",{attrs:{id:"pseudo-random-numbers"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#pseudo-random-numbers"}},[t._v("#")]),t._v(" Pseudo Random Numbers")]),t._v(" "),s("p",[t._v("Java provides, as part of the "),s("code",[t._v("utils")]),t._v(" package, a basic pseudo-random number generator, appropriately named "),s("code",[t._v("Random")]),t._v(". This object can be used to generate a pseudo-random value as any of the built-in numerical datatypes ("),s("code",[t._v("int")]),t._v(", "),s("code",[t._v("float")]),t._v(", etc). 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It has one drawback of being considerably slower than "),s("code",[t._v("Random")]),t._v(" and other linear PRNGs such as "),s("a",{attrs:{href:"https://en.wikipedia.org/wiki/Mersenne_Twister",target:"_blank",rel:"noopener noreferrer"}},[t._v("Mersenne Twister"),s("OutboundLink")],1),t._v(" and "),s("a",{attrs:{href:"https://en.wikipedia.org/wiki/Xorshift",target:"_blank",rel:"noopener noreferrer"}},[t._v("Xorshift"),s("OutboundLink")],1),t._v(", however.")]),t._v(" "),s("p",[t._v("Note that SecureRandom implementation is both platform and provider dependent. The default "),s("code",[t._v("SecureRandom")]),t._v(" (given by "),s("code",[t._v("SUN")]),t._v(" provider in "),s("code",[t._v("sun.security.provider.SecureRandom")]),t._v("):")]),t._v(" "),s("ul",[s("li",[t._v("on Unix-like systems, seeded with data from "),s("code",[t._v("/dev/random")]),t._v(" and/or "),s("code",[t._v("/dev/urandom")]),t._v(".")]),t._v(" "),s("li",[t._v("on Windows, seeded with calls to "),s("code",[t._v("CryptGenRandom()")]),t._v(" in "),s("a",{attrs:{href:"https://en.wikipedia.org/wiki/Microsoft_CryptoAPI",target:"_blank",rel:"noopener noreferrer"}},[t._v("CryptoAPI"),s("OutboundLink")],1),t._v(".")])]),t._v(" "),s("h2",{attrs:{id:"generating-random-numbers-with-a-specified-seed"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#generating-random-numbers-with-a-specified-seed"}},[t._v("#")]),t._v(" Generating Random Numbers with a Specified Seed")]),t._v(" "),s("div",{staticClass:"language-java 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"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("ThreadLocalRandom")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("current")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n"),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("//Set the instance's seed.")]),t._v("\ntlr"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("setSeed")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token number"}},[t._v("12345L")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token 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                      "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("break")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n                    "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n                "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n                \n                "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// if it hasnt been taken then remove one from the spots")]),t._v("\n                "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("if")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("!")]),t._v("taken"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n                    newRandSpot"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("--")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n                    \n                    "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// if we have gone though all the spots then set the value")]),t._v("\n                    "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("if")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("newRandSpot"),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("==")]),s("span",{pre:!0,attrs:{class:"token number"}},[t._v("0")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n                        randomNumbers"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("[")]),t._v("q"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("]")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" t"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n                    "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n                "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n            "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n        "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n        "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("return")]),t._v(" randomNumbers"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n    "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("else")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n        "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// invalid can't have a length larger then the range of possible numbers")]),t._v("\n    "),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n    "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("return")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("null")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n\n")])])]),s("p",[t._v("The method works by looping though an array that has the size of the requested length and finds the remaining length of possible numbers. It sets a random number of those possible numbers "),s("code",[t._v("newRandSpot")]),t._v(" and finds that number within the non taken number left. It does this by looping through the range and checking to see if that number has already been taken.")]),t._v(" "),s("p",[t._v("For example if the range is 5 and the length is 3 and we have already chosen the number 2. Then we have 4 remaining numbers so we get a random number between 1 and 4 and we loop through the range(5) skipping over any numbers that we have already used(2).")]),t._v(" "),s("p",[t._v("Now let's say the next number chosen between 1 & 4 is 3. On the first loop we get 1 which has not yet been taken so we can remove 1 from 3 making it 2. Now on the second loop we get 2 which has been taken so we do nothing. We follow this pattern until we get to 4 where once we remove 1 it becomes 0 so we set the new randomNumber to 4.")]),t._v(" "),s("h2",{attrs:{id:"generating-random-number-using-apache-common-lang3"}},[s("a",{staticClass:"header-anchor",attrs:{href:"#generating-random-number-using-apache-common-lang3"}},[t._v("#")]),t._v(" Generating Random number using apache-common lang3")]),t._v(" "),s("p",[t._v("We can use "),s("code",[t._v("org.apache.commons.lang3.RandomUtils")]),t._v(" to generate random numbers using a single line.")]),t._v(" "),s("div",{staticClass:"language-java extra-class"},[s("pre",{pre:!0,attrs:{class:"language-java"}},[s("code",[s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" x "),s("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("RandomUtils")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("nextInt")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token number"}},[t._v("1")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token number"}},[t._v("1000")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n")])])]),s("p",[t._v("The method "),s("code",[t._v("nextInt(int startInclusive, int endExclusive)")]),t._v(" takes a range.")]),t._v(" "),s("p",[t._v("Apart from int, we can generate random "),s("code",[t._v("long")]),t._v(", "),s("code",[t._v("double")]),t._v(", "),s("code",[t._v("float")]),t._v(" and "),s("code",[t._v("bytes")]),t._v(" using this class.")]),t._v(" "),s("p",[s("code",[t._v("RandomUtils")]),t._v(" class contains the following methods-")]),t._v(" "),s("div",{staticClass:"language-java extra-class"},[s("pre",{pre:!0,attrs:{class:"language-java"}},[s("code",[s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("static")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("byte")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("[")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("]")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("nextBytes")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" count"),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("//Creates an array of random bytes.")]),t._v("\n"),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("static")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("double")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token function"}},[t._v("nextDouble")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),s("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),s("span",{pre:!0,attrs:{class:"token comment"}},[t._v("//Returns a random double within 0 - 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Those numbers are created with a "),s("a",{attrs:{href:"https://en.wikipedia.org/wiki/Pseudorandom_number_generator",target:"_blank",rel:"noopener noreferrer"}},[t._v("pseudorandom number generator"),s("OutboundLink")],1),t._v(".")])])}),[],!1,null,null,null);a.default=e.exports}}]);