There are two main methods of inputting Japanese on computers. One is via romanized Japanese, rōmaji, and the other is via keyboard keys corresponding to the Japanese kana.
Japanese keyboards have both kana and roman letters indicated. The JIS X 6002 keyboard layout keeps the roman letters in the usual "qwerty" layout, with numbers above them. Many of the non-alphanumeric symbols are the same as on English-language keyboards, but some symbols are located in other places.
The kana symbols are also ordered in a consistent way across different keyboards. For example, the ''Q W E R T Y'' keys correspond to ''た て い す か ん'' (Ta Te I Su Ka N) when the computer is used for direct kana input. These types of keyboards are rarely found outside Japan. However, there is no special hardware requirement for a user to input Japanese via the romaji input method. Most newer operating systems allow this function, even when the operating system itself is in English or another non-Japanese language.
Since Japanese input requires switching between roman and kana entry modes, and also conversion between kana and kanji, there are several special keys on the keyboard. On non-Japanese keyboards, Option key or Control key sequences can do all of the tasks mentioned below.
A key labelled "半角／全角 漢字" (hankaku/zenkaku kanji) switches between kanji conversion and non-conversion. It is situated under the "Escape" key at the top left of the keyboard.
The 無変換 key at the left of the space key allows for switching between conversion into hiragana, katakana, and half-width katakana (see What is half-width katakana?).
The 変換 (henkan) key on the right of the space bar instructs the computer to convert the latest kana characters into kanji. The space key also serves the same purpose, since Japanese writing does not use spaces. (See Is Japanese ever written with spaces between the words?).
The system used to input Japanese on mobile phones is based on the numerical keypad. Each number is associated with a particular sequence of kana, such as ''ka'', ''ki'', ''ku'', ''ke'', ''ko'' for '2', and the button is pressed repeatedly to get the correct kana. Dakuten and handakuten marks, punctuation, and other symbols can be added by other buttons in the same way. Kana to kanji conversion is done via the arrow and other keys.
After the kana have been input, they may be left as they are by pressing "Enter", converted to full-width or half-width katakana via " 無変換" (muhenkan), or converted into kanji by pressing 変換 or the space bar.
The Japanese language has many homonyms, so conversion of kana into kanji may involve multiple choices between similarly-pronounced kanji. The kana to kanji converter offers a list of candidate kanji writings for the input kana, and the user may use the space bar or arrow keys to scroll through the list of candidates until he or she reaches the correct writing. On reaching the correct written form, pressing the ''Enter'' or 変換 (henkan) key ends the conversion process.
If the hiragana is required, pressing the ''Enter'' key immediately after the characters are entered will end the conversion process and results in the hiragana as typed. Kakakana words will usually be presented as options along with the kanji choices. To force katakana conversion, pressing 無変換 (muhenkan) switches between katakana or hiragana.
Kana to kanji convertors, (known collectively as input method editors, or IME, after the name of the Microsoft product), allow conversion of multiple kana words into kanji at once, freeing the user from having to do a conversion at each stage. The user can convert at any stage of input by pressing the space bar or henkan button, and the convertor attempts to guess the correct division of words. Some IMEs may display a brief definition of each word in order to help the user choose the correct kanji.
Sometimes the kana to kanji convertor may guess the correct kanji for all the words, but if it does not, the cursor (arrow) keys may be used to move backwards and forwards between candidate words. If the selected word boundaries are incorrect, the word boundaries can be moved using the control key plus the arrow keys.
Modern systems learn the user's preferences for conversion and put the most recently selected candidates at the top of the conversion list, and also remember which words the user is likely to use when considering word boundaries.
The systems used on mobile phones go even further, and try to guess entire phrases or sentences. After a few kana have been entered, the phone automatically offers entire phrases or sentences as possible completion candidates, jumping beyond what has been input. This is usually based on words sent in previous messages.
This page was partly written by Paul Blay when it was part of the "Wiki sci.lang.japan FAQ" (see FAQ Format).
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