Suppose we have to match characters that belong to one class but not to another in a composite character class pattern. There is no separate operator for the subtraction operation. Subtraction is performed by using the intersection operator, &&, and a negated inner character class.
For example, consider the following composite character class:
It will match the digits, 0 to 9, except the digits, 3 to 6. This character class can also be written as a union of two character classes:
We can also just use a simple character class, as ...