Typical pseudo-random number generators calculate new numbers based on previous ones, so in theory they are completely deterministic. The only randomness is guaranteed by providing a good seed (initialization of the random number generation algorithm). As long as the random numbers aren't very security critical (this would require "real" random numbers), such a recursive random number generator often satisfies the needs. The recursive generation can be expressed without any "external" functions, once a seed was provided. There are a couple of algorithms solving this problem. A good example is the Linear Congruential Generator.
/**
*
*/
package com.kartik.org;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;
/**
* @author kmandal
*
*/
public class KartikRandomNumber implements Serializable{
private static final long serialVersionUID = 1L;
/**
* @param args
*/
public static void main(String[] args) {
System.out.println(myRand());
}
public static int myRand ()
{
int next = testSerialversionRead();
next = ((next * next * next ) / 100 ) % 10000 ;
testSerialversionWrite(next);
return next ;
}
/*public static int myRand (int next) // Generate a 4 digit pseudo-random integer
{
// int next = 3251 ;
next = ((next * next) / 100 ) % 10000 ;
testSerialversionWrite(next);
return next ;
}
public static int myRandInRange ( int min, int max ) // max-min must be <10000!!
{
int taxn=testSerialversionRead();
return myRand(taxn) % (max+1-min) + min;
}*/
public static void testSerialversionWrite(int txn) {
try{
FileOutputStream fout = new FileOutputStream("d:\\txnsearch1.ser");
ObjectOutputStream oos = new ObjectOutputStream(fout);
oos.writeObject(txn);
oos.close();
}catch(Exception ex){
ex.printStackTrace();
}
}
public static int testSerialversionRead() {
int txn = 200;
try{
FileInputStream fin = new FileInputStream("d:\\txnsearch1.ser");
ObjectInputStream ois = new ObjectInputStream(fin);
txn = (int) ois.readObject();
ois.close();
}catch(Exception ex){
ex.printStackTrace();
}
return txn;
}
}
OutPut:
-7418
-3455
2515
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I am Kartik Chandra Mandal from Bangalore, India. Working as software engineer in Java technology. Have good knowledge of OWASP and CSRF in security for applications and it's implementation in Java technology.