Presents your 
JAVA E-NEWSLETTER for July 8, 2002

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MANAGE A SERIES OF OPTIONS WITH THE BITSET CLASS

If you want to emulate the C programming style of storing many boolean
values in a single variable, use the java.util.BitSet class rather than
compiling them into a primitive 'long' variable.

The BitSet class is useful for managing a series of options in a concise
and low-memory way. It provides a way to store N bits into a generic
object. The class itself must decide how much memory it should use and when
to change strategies. All the developer has to worry about is which bits
to set. Bits are automatically turned off until they are set.

Here's how to create a BitSet:

// for the value '01001'
BitSet bits = new BitSet( );
bits.set(1);
bits.set(4);

It's possible to automatically output a BitSet by using the toString
method. The output data will resemble the following:

{1, 4}

You can also use a method that shows the output as the binary, such as:

static public String output(BitSet bits) {
    int size = bits.length( );
    StringBuffer buffer = new StringBuffer( );
    for(int i=0; i<size; i++) {
        buffer.append( (bits.get(i))?"1":"0" );
    }
    return buffer.toString( );
}

Rather than outputting '{1, 4}', the above example will output '01001'.

BitSets can be merged together via the Boolean algebra methods and, xor,
and andNot. For example, 10001 and 00001 will return 10000.

The size( ) method returns the number of bits of space currently in use
rather than the number if bits in a BitSet. However, the length( ) method
only returns the number of bits up until the highest "true" value, plus
one. This can cause a problem with the output(BitSet) method--"10001
andNot 00001" will equal "1" because the higher 0s won't be shown.

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