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White cells are the leading bytes for a sequence of multiple bytes, the length shown at the left edge of the row. The text shows the Unicode blocks encoded by sequences starting with this byte, and the hexadecimal code point shown in the cell is the lowest character value encoded using that leading byte.
Red cells must never appear in a valid UTF-8 sequence. The first two red cells C0 and C1 could be used only for a two-byte encoding of a 7-bit ASCII character which should be encoded in one byte; as described below such "overlong" sequences are disallowed.
Pink cells are the leading bytes for a sequence of multiple bytes, of which some, but not all, possible continuation sequences are valid. E0 and F0 could start overlong encodings, in this case the lowest non-overlong-encoded code point is shown.
In principle, it would be possible to inflate the number of bytes in an encoding by padding the code point with leading 0s. This is called an overlong encoding.
The standard specifies that the correct encoding of a code point use only the minimum number of bytes required to hold the significant bits of the code point. Longer encodings are called overlong and are not valid UTF-8 representations of the code point. This rule maintains a one-to-one correspondence between code points and their valid encodings, so that there is a unique valid encoding for each code point.
This ensures that string comparisons and searches are well-defined. This allows the byte 00 to be used as a string terminator. Many earlier decoders would happily try to decode these. This guarantees that it will neither interpret nor emit an ill-formed code unit sequence. Many UTF-8 decoders throw exceptions on encountering errors. Early versions of Python 3. More recent converters translate the first byte of an invalid sequence to a replacement character and continue parsing with the next byte.
These error bytes will always have the high bit set. This avoids denial-of-service bugs, and it is very common in text rendering such as browser display, since mangled text is probably more useful than nothing for helping the user figure out what the string was supposed to contain. These replacement algorithms are " lossy ", as more than one sequence is translated to the same code point. This means that it would not be possible to reliably convert back to the original encoding, therefore losing information.
But this runs into practical difficulties: The large number of invalid byte sequences provides the advantage of making it easy to have a program accept both UTF-8 and legacy encodings such as ISO Software can check for UTF-8 correctness, and if that fails assume the input to be in the legacy encoding. To preserve these invalid UTF sequences, their corresponding UTF-8 encodings are sometimes allowed by implementations despite the above rule. This spelling is used in all the Unicode Consortium documents relating to the encoding.
Other descriptions that omit the hyphen or replace it with a space, such as "utf8" or "UTF 8", are not accepted as correct by the governing standards. Supported Windows versions, i. Windows 7 and later, have codepage , as a synonym for UTF-8 with better support than in older Windows ,  and Microsoft has a script for Windows 10, to enable it by default for its notepad program. The following implementations show slight differences from the UTF-8 specification.
In such programs each half of a UTF surrogate pair is encoded as its own three-byte UTF-8 encoding, resulting in six-byte sequences rather than four bytes for characters outside the Basic Multilingual Plane.
Although this non-optimal encoding is generally not deliberate, a supposed benefit is that it preserves UTF binary sorting order when CESU-8 is binary sorted. In normal usage, the Java programming language supports standard UTF-8 when reading and writing strings through InputStreamReader and OutputStreamWriter if it is the platform's default character set or as requested by the program.
However it uses Modified UTF-8 for object serialization  among other applications of DataInput and DataOutput , for the Java Native Interface ,  and for embedding constant strings in class files.
Many systems that deal with UTF-8 work this way without considering it a different encoding, as it is simpler. Software that is not aware of multibyte encodings will display the BOM as three garbage characters at the start of the document, e.
The Unicode Standard neither requires nor recommends the use of the BOM for UTF-8, but warns that it may be encountered at the start of a file as a transcoding artifact.
By early , the search was on for a good byte stream encoding of multi-byte character sets. The draft ISO standard contained a non-required annex called UTF-1 that provided a byte stream encoding of its bit code points. This encoding was not satisfactory on performance grounds, among other problems, and the biggest problem was probably that it did not have a clear separation between ASCII and non-ASCII: The table below was derived from a textual description in the annex.
Dave Prosser of Unix System Laboratories submitted a proposal for one that had faster implementation characteristics and introduced the improvement that 7-bit ASCII characters would only represent themselves; all multibyte sequences would include only bytes where the high bit was set.
A modification by Ken Thompson of the Plan 9 operating system group at Bell Labs made it somewhat less bit-efficient than the previous proposal but crucially allowed it to be self-synchronizing , letting a reader start anywhere and immediately detect byte sequence boundaries. It also abandoned the use of biases and instead added the rule that only the shortest possible encoding is allowed; the additional loss in compactness is relatively insignificant, but readers now have to look out for invalid encodings to avoid reliability and especially security issues.
Thompson's design was outlined on September 2, , on a placemat in a New Jersey diner with Rob Pike. They are all the same in their general mechanics, with the main differences being on issues such as allowed range of code point values and safe handling of invalid input. From Wikipedia, the free encyclopedia. UTF-8 history , From: Wed, 30 Apr When converted to a java.
Date , the date is set to LocalTime is also supported on Java 8 and later versions. Time is limited to milliseconds, use String or java. LocalTime if you need nanosecond resolution. Date , with the time set to LocalDate is also supported on Java 8 and later versions.
The timestamp data type. The format is yyyy- MM -dd hh: Stored internally as a BCD -encoded date, and nanoseconds since midnight. If fractional seconds precision is specified it should be from 0 to 9, 6 is default.
Date may be used too. LocalDateTime is also supported on Java 8 and later versions. The timestamp with time zone data type. Stored internally as a BCD -encoded date, nanoseconds since midnight, and time zone offset in minutes. Instant are also supported on Java 8 and later versions. Values of this data type are compared by UTC values. It means that Represents a byte array.
For very long arrays, use BLOB. The maximum size is 2 GB, but the whole object is kept in memory when using this data type. The precision is a size constraint; only the actual data is persisted. This type allows storing serialized Java objects. Internally, a byte array is used. Serialization and deserialization is done on the client side only. Deserialization is only done when getObject is called. Java operations cannot be executed inside the database engine for security reasons.