Why doesn t the Scanner class have a nextChar method

Question

This is really a curiosity more than a problem     Why doesn t the Scanner class have a nextChar   method  It seems like it should when you consider the fact that it has next  nextInt  nextLine etc method   I realize you can simply do the following   userChar   in next   charAt 0   System out println  userChar       But why not have a nextChar   method

User · Answer

I would imagine that it has to do with encoding. A char is 16 bytes and some encodings will use one byte for a character whereas another will use two or even more. When Java was originally designed, they assumed that any Unicode character would fit in 2 bytes, whereas now a Unicode character can require up to 4 bytes (UTF-32). There is no way for Scanner to represent a UTF-32 codepoint in a single char.

You can specify an encoding to Scanner when you construct an instance, and if not provided, it will use the platform character-set. But this still doesn't handle the issue with 3 or 4 byte Unicode characters, since they cannot be represented as a single char primitive (since char is only 16 bytes). So you would end up getting inconsistent results.

User · Answer

The reason is that the Scanner class is designed for reading in whitespace-separated tokens  It s a convenience class that wraps an underlying input stream  Before scanner all you could do was read in single bytes  and that s a big pain if you want to read words or lines  With Scanner you pass in System in  and it does a number of read   operations to tokenize the input for you  Reading a single character is a more basic operation    Source   You can use  char  System in read

User · Answer

The Scanner class is bases on logic implemented in String next Pattern  method  The additional API method like nextDouble   or nextFloat    Provide the pattern inside    Then class description says       A simple text scanner which can parse primitive types and strings   using regular expressions       A Scanner breaks its input into tokens using a delimiter pattern    which by default matches whitespace  The resulting tokens may then be   converted into values of different types using the various next   methods    From the description it can be sad that someone has forgot about char as it is a primitive type for sure    But the concept of class is to find patterns  a char has no pattern is just next character  And this logic IMHO caused that nextChar has not been implemented    If you need to read a filed char by char you can used more efficient class

User · Answer

To get a definitive reason  you d need to ask the designer s  of that API   But one possible reason is that the intent of a  hypothetical  nextChar would not fit into the scanning model very well    If nextChar   to behaved like read   on a Reader and simply returned the next unconsumed character from the scanner  then it is behaving inconsistently with the other next lt Type gt  methods   These skip over delimiter characters before they attempt to parse a value  If nextChar   to behaved like  say  nextInt then    the delimiter skipping would be  unexpected  for some folks  and there is the issue of whether it should accept a single  raw  character  or a sequence of digits that are the numeric representation of a char  or maybe even support escaping or something1     No matter what choice they made  some people wouldn t be happy   My guess is that the designers decided to stay away from the tarpit     1 - Would vote strongly for the raw character approach     but the point is that there are alternatives that need to be analysed  etc

User · Answer

According to the javadoc a Scanner does not seem to be intended for reading single characters  You attach a Scanner to an InputStream  or something else  and it parses the input for you  It also can strip of unwanted characters  So you can read numbers  lines  etc  easily  When you need only the characters from your input  use a InputStreamReader for example

[java] Why doesn't the Scanner class have a nextChar method?

Examples related to java