tl;dr
You asked:
Does java.util.UUID generates special characters?
No. A UUID is actually a 128-bit value, not text.
A UUID’s textual representation is canonically a string of hex digits (0-9, a-f, A-F) plus hyphens.
You asked:
What are the type of each character (eg- Uppercase, lower case, digits) generated by UUID.
As required by the UUID spec, any a-to-f characters in the hex string representing a UUID value must be in all lowercase. But violations abound.
UUID ≠ text
To clarify, a UUID is actually a 128-bit value, not text, not digits.
You could think of them as 128-bit unsigned integers. But they are not actually numbers, as certain bit positions have semantics, specific meanings. Which bits have which meanings varies by variant and by version of UUID.
Hex string
Humans don’t do well reading and writing 128 bits as 128 1 and 0 characters. When a UUID needs to be written for human consumption, we use a base-16 Hexadecimal (digits 0–9 and letters a–f) string. We use 32 hex characters grouped with 4 hyphens to represent those 128 bits in a total of 36 characters. For example:
550e8400-e29b-41d4-a716-446655440000
No “Special” Characters
As for “special characters” mentioned in the Question, you will only see these 23 possible characters in a hex-string representation of a UUID:
abcdefABCDEF1234567890-
Lowercase Required By Spec
The latest international spec dated 2008-08 states (emphasis mine):
6.5.4 Software generating the hexadecimal representation of a UUID shall not use upper case letters.
NOTE – It is recommended that the hexadecimal representation used in all human-readable formats be restricted to lower-case letters. Software processing this representation is, however, required to accept both upper and lower case letters as specified in 6.5.2.
Violations Common
However, Microsoft, Apple, and others commonly violate the lowercase rule. At one point Microsoft released software that generated mixed case (using both upper- and lowercase), apparently an unintended feature.
So do as the spec says:
- Use lowercase for output.
- Tolerate either lowercase or uppercase for input.
The Java documentation for the UUID class’ toString method documents in BNF that uppercase is allowed when generating a string, in contradiction to the UUID standard specification. However the actual behavior of the class and its toString method in the Oracle implementation for Java 8 is correct, using lowercase for output but tolerating either uppercase or lowercase for input.
Input in either lower-/uppercase:
UUID uuidFromLowercase = UUID.fromString ( "897b7f44-1f31-4c95-80cb-bbb43e4dcf05" );
UUID uuidFromUppercase = UUID.fromString ( "897B7F44-1F31-4C95-80CB-BBB43E4DCF05" );
Output to lowercase only:
System.out.println ( "uuidFromLowercase.toString(): " + uuidFromLowercase );
System.out.println ( "uuidFromUppercase.toString(): " + uuidFromUppercase );
uuidFromLowercase.toString(): 897b7f44-1f31-4c95-80cb-bbb43e4dcf05
uuidFromUppercase.toString(): 897b7f44-1f31-4c95-80cb-bbb43e4dcf05
See this code run live in IdeOne.com.
Nil value
When the UUID is not yet known, you can use a special UUID consisting of all zeros.
00000000-0000-0000-0000-000000000000
Example Values
You can see some examples of UUID values by using any of the many web sites that generate values. For example:
- https://www.uuidgenerator.net/
Or use a command-line tool. Nearly every operating system comes bundled with such a tool. On macOS, launch Terminal.app and type uuidgen.