How do I read input character-by-character in Java

Question

I am used to the c-style getchar    but it seems like there is nothing comparable for java  I am building a lexical analyzer  and I need to read in the input character by character   I know I can use the scanner to scan in a token or line and parse through the token char-by-char  but that seems unwieldy for strings spanning multiple lines  Is there a way to just get the next character from the input buffer in Java  or should I just plug away with the Scanner class   The input is a file  not the keyboard

User · Answer

If I were you I d just use a scanner and use   nextByte      You can cast that to a char and you re good

User · Answer

Use Reader read    A return value of -1 means end of stream  else  cast to char   This code reads character data from a list of file arguments   public class CharacterHandler         Java 7 source level     public static void main String   args  throws IOException              replace this with a known encoding if possible         Charset encoding   Charset defaultCharset            for  String filename   args                File file   new File filename               handleFile file  encoding                        private static void handleFile File file  Charset encoding              throws IOException           try  InputStream in   new FileInputStream file                Reader reader   new InputStreamReader in  encoding                   buffer for efficiency              Reader buffer   new BufferedReader reader                 handleCharacters buffer                        private static void handleCharacters Reader reader              throws IOException           int r          while   r   reader read       -1                char ch    char  r              System out println  Do something with     ch                       The bad thing about the above code is that it uses the system s default character set  Wherever possible  prefer a known encoding  ideally  a Unicode encoding if you have a choice   See the Charset class for more   If you feel masochistic  you can read this guide to character encoding     One thing you might want to look out for are supplementary Unicode characters - those that require two char values to store  See the Character class for more details  this is an edge case that probably won t apply to homework

User · Answer

Combining the recommendations from others for specifying a character encoding and buffering the input  here s what I think is a pretty complete answer   Assuming you have a File object representing the file you want to read   BufferedReader reader   new BufferedReader      new InputStreamReader          new FileInputStream file           Charset forName  UTF-8      int c  while  c   reader read       -1      char character    char  c       Do something with your character

User · Answer

Another option is to not read things in character by character -- read the entire file into memory   This is useful if you need to look at the characters more than once   One trivial way to do that is         Read the contents of a file into a string buffer             public static void readFile File file  StringBuffer buf          throws IOException           FileReader fr   null      try         fr   new FileReader file         BufferedReader br   new BufferedReader fr         char   cbuf   new char  int  file length           br read cbuf           buf append cbuf         br close              finally         if  fr    null            fr close

User · Answer

Wrap your reader in a BufferedReader  which maintains a buffer allowing for much faster reads overall   You can then use read   to read a single character  which you ll need to cast    You can also use readLine   to fetch an entire line and then break that into individual characters   The BufferedReader also supports marking and returning  so if you need to  you can read a line multiple times   Generally speaking  you want to use a BufferedReader or BufferedInputStream  on top of whatever stream you are actually using since the buffer they maintain will make multiple reads much faster

User · Answer

Wrap your input stream in a buffered reader then use the read method to read one byte at a time until the end of stream   import java io BufferedReader  import java io IOException  import java io InputStreamReader   public class Reader        public static void main String   args  throws IOException            BufferedReader buffer   new BufferedReader                   new InputStreamReader System in            int c   0          while  c   buffer read       -1                char character    char  c                        System out println character

User · Answer

In java 5 new feature added that is Scanner method who gives the chance to read input character by character in java   for instance  for use Scanner method import java util Scanner  after in main method define  Scanner myScanner   new Scanner System in     for read character   char anything myScanner findInLine      charAt 0     you anything store single character  if you want more read more character declare more object like anything1 anything2    more example for your answer please check in your hand copy paste        import java util Scanner       class ReverseWord         public static void main String args         Scanner myScanner new Scanner System in       char c1 c2 c3 c4       c1   myScanner findInLine      charAt 0           c2   myScanner findInLine      charAt 0       c3   myScanner findInLine      charAt 0       c4   myScanner findInLine      charAt 0        System out print c4       System out print c3       System out print c2       System out print c1       System out println

User · Answer

This will print 1 character per line from the file       try            FileInputStream inputStream   new FileInputStream theFile           while  inputStream available    gt  0                inputData   inputStream read                System out println  char  inputData                      inputStream close          catch  IOException ioe            System out println  Trouble reading from the file      ioe getMessage

User · Answer

You have several options if you use BufferedReader  This buffered reader is faster than Reader so you can wrap it    BufferedReader reader   new BufferedReader new FileReader path    reader read char   buffer     this reads line into char array  You have similar options  Look at documentation

[java] How do I read input character-by-character in Java?

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