Constructor

BigInteger(byte[] val): Translates a byte array containing the two's-complement binary representation of a BigInteger into a BigInteger.
BigInteger(int signum, byte[] magnitude): Translates the sign-magnitude representation of a BigInteger into a BigInteger.
BigInteger(int bitLength, int certainty, Random rnd): Creates a randomly generated positive BigInteger that is probably prime, with the specified bitLength.
BigInteger(int numBits, Random rnd): Creates a randomly generated BigInteger, uniformly distributed over the range 0 to (2numBits - 1), inclusive.
BigInteger(String val): Translates the decimal String representation of a BigInteger into a BigInteger.
BigInteger(String val, int radix): Translates the String representation of a BigInteger in the specified radix into a BigInteger.

The following code use

new BigInteger(byte[] val)

to create a BigInteger.


import java.math.BigInteger;

public class Main {
  public static void main(String[] argv) throws Exception {
    // A negative value
    byte[] bytes = new byte[] { (byte) 0xFF, 0x00, 0x00 }; // -65536
    // A positive value
    bytes = new byte[] { 0x1, 0x00, 0x00 }; // 65536
    BigInteger bi = new BigInteger(bytes);
  }
}

The following code use

new BigInteger(String val)

to create a BigInteger.


import java.math.BigInteger;

/*
Here's Long.MAX_VALUE: 9223372036854775807
Here's a bigger number: 3419229223372036854775807
Here it is as a double: 3.419229223372037E24
 */
public class MainClass {
  public static void main(String[] args) {
    System.out.println("Here's Long.MAX_VALUE: " + Long.MAX_VALUE);
    BigInteger bInt = new BigInteger("3419229223372036854775807");
    System.out.println("Here's a bigger number: " + bInt);
    System.out.println("Here it is as a double: " + bInt.doubleValue());
  }

}

You can set the radix for the string value passed in with

new BigInteger(String val, int radix)


import java.math.BigInteger;

public class Main {
  public static void main(String[] argv) throws Exception {
    BigInteger bi = new BigInteger("4407760", 8);

  }
}

new BigInteger(int bitLength, int certainty, Random rnd) creates a BigInteger with a random number


import java.math.BigInteger;
import java.security.SecureRandom;

public class Main {
  public static void main(String[] args) throws Exception {
    int bitLength = 512; // 512 bits
    SecureRandom rnd = new SecureRandom();
    int certainty = 90; // 1 - 1/2(90) certainty
    System.out.println("BitLength : " + bitLength);
    BigInteger mod = new BigInteger(bitLength, certainty, rnd);
    BigInteger exponent = BigInteger.probablePrime(bitLength, rnd);
    BigInteger n = BigInteger.probablePrime(bitLength, rnd);

    BigInteger result = n.modPow(exponent, mod);
    System.out.println("Number ^ Exponent MOD Modulus = Result");
    System.out.println("Number");
    System.out.println(n);
    System.out.println("Exponent");
    System.out.println(exponent);
    System.out.println("Modulus");
    System.out.println(mod);
    System.out.println("Result");
    System.out.println(result);
  }
}

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