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genopri-shcs/project/PPPCommons/src/crypto/PrimeGenerator.java
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PrimeGenerator.java
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/*
* To change this template, choose Tools | Templates
* and open the template in the editor.
*/
package crypto;
import java.math.BigInteger;
import java.util.Vector;
/**
*
* @author raisaro
*/
public class PrimeGenerator {
private BigInteger gen; // This number occurs just before the
// smallest generated prime.
/**
* Initializes the generator.
*/
public PrimeGenerator() {
gen = BigInteger.ONE;
}
/**
* Obtains a specified number of primes.
*
* @param start No primes will be returned whose values are less than this.
* @param num The number of primes to generate.
*
* @return A list of prime integers.
*/
public Vector< Long > getPrimes( long start, int num ) {
Vector< Long > p; // The primes found.
p = new Vector< Long >( num );
gen = BigInteger.valueOf( start - 1 );
for( int i = 0; i < num; i++ ) {
gen = gen.nextProbablePrime();
p.add( gen.longValue() );
}
return p;
}
/**
* Obtains a specified number of primes.
*
* @param digits The primes must have at least this number of digits.
* @param num The number of primes to generate.
*
* @return A list of prime numbers.
*/
public Vector< BigInteger > getBigPrimes( int digits, int num ) {
Vector< BigInteger > p; // The primes found.
String start; // Primes must be greater than this number.
p = new Vector< BigInteger >( num );
start = String.valueOf( '1' );
for( int i = 1; i < digits; i++ ) {
start = start.concat( "0" );
}
gen = new BigInteger( start );
for( int i = 0; i < num; i++ ) {
gen = gen.nextProbablePrime();
p.add( gen );
}
return p;
}
/**
* Obtains all primes within a range of values. The lower and
* upper bound are inclusive, so they will appear in the list of
* primes if they are prime values.
*
* @param lb Lower bound of the range.
* @param ub Upper bound of the range.
*
* @return A list of prime integers.
*/
public Vector< Long > getPrimesBetween( long lb, long ub ) {
Vector< Long > p; // The primes found.
BigInteger stop; // Indicates when to stop generating values.
p = new Vector< Long >();
gen = BigInteger.valueOf( lb - 1 );
stop = BigInteger.valueOf( ub );
while( gen.compareTo( stop ) <= 0 ) {
gen = gen.nextProbablePrime();
p.add( gen.longValue() );
}
return p;
}
/**
* Tests the prime generator by generating and printing out a
* list of primes.
*
* @param args The number of primes to generate and the starting integer.
*/
// public static void main( String[] args ) {
//
// long start; // Starting number (all primes will be >= start).
// int num; // Number of primes to generate.
// PrimeGenerator pg; // Class instance used to generate primes.
// Vector< Long > primes; // The primes returned by the generator.
//
// // Check the number of arguments, and print out a usage
// // message if it isn't right.
// if( args.length != 2 ) {
// System.err.println( "Usage: java PrimeGenerator n start" );
// System.err.println( "<n> = number of primes" );
// System.err.println( "<start> = starting integer" );
// System.exit( 1 );
// }
//
// try {
// // Obtain the arguments and instantiate the prime generator.
// num = Integer.parseInt( args[ 0 ] );
// start = Long.parseLong( args[ 1 ] );
// pg = new PrimeGenerator();
// // Obtain and print out the primes from the generator.
// primes = pg.getPrimes( start, num );
// for( int i = 0; i < primes.size(); i++ ) {
// System.out.println( primes.get( i ) );
// }
// } catch( NumberFormatException n ) {
// System.err.println( "One of the arguments is not a number. " +
// "Please try again." );
// System.exit( 1 );
// }
//
// }
}
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