Presents your 
JAVA E-NEWSLETTER for March 10, 2003

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MANIPULATE LARGE BITS WITH BIGINTEGER

Bitwise logic in programs usually involves shifting a number back and
forth and performing bitwise operations on bits to determine which ones are
set. If you need to manipulate numbers with 64 bits or less, you can use
a long or an int.

If you need to manipulate numbers with more than 64 bits, you'll need to
use the java.math.BigInteger class. (BigInteger is part of the core API
and has been since 1.1.)
http://java.sun.com/j2se/1.3/docs/api/java/math/BigInteger.html

The BigInteger type is used for manipulating large integers. There are
several constructors, but the most straightforward one takes a
java.lang.String object representing the number you want to manipulate. 
For example:

BigInteger bi = new BigInteger("FFFFFFFFFFFFFFF", 16);

In the preceding code, an instance of BigInteger was created using the
BigInteger constructor that takes a String and an integer representing 
the number's radix.

Once you've created your instance, you can perform operations on it by
calling any of the methods provided. Like java.lang.String, the BigInteger
class is immutable, so all of the methods that perform operations return
an instance of a new BigInteger that is the result of the operation.

There are methods for all of the basic math operations--add, subtract,
divide, multiply--as well as all of the bit operations you'll need--and,
or, xor, andNot, shiftRight, shiftLeft, etc. Here are some method examples:

BigInteger result = bi.multiply(new BigInteger("2"));
System.out.println(result);

result = bi.divide(new BigInteger("2"));
System.out.println(result);

result = bi.add(new BigInteger("232"));
System.out.println(result);

result = bi.subtract(new BigInteger("23122"));
System.out.println(result);

result = bi.shiftRight(10);
System.out.println(result);

Within the BigInteger class, there are other useful constructors and
many other methods that can make your big number manipulation easier.

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