Java PushbackReader class

Introduction

The PushbackReader class can read and return characters to the input stream.

Here are its two constructors: 

PushbackReader(Reader inputStream)  
PushbackReader(Reader inputStream, int bufSize)

PushbackReader has unread() methods to return one or more characters to the invoking input stream.

It has the three forms shown here: 

void unread(int  ch) throws IOException  
void unread(char  buffer [ ]) throws IOException  
void unread(char  buffer [ ], int  offset, int numChars) throws IOException 


import java.io.CharArrayReader;
import java.io.IOException;
import java.io.PushbackReader;

public class Main {
   public static void main(String args[]) {
      String s = "if (a == 4) a = 0;\n";
      char buf[] = new char[s.length()];
      s.getChars(0, s.length(), buf, 0);
      CharArrayReader in = new CharArrayReader(buf);

      int c;//from   w  ww . ja v  a  2s.  c  om

      try (PushbackReader f = new PushbackReader(in)) {
         while ((c = f.read()) != -1) {
            switch (c) {
            case '=':
               if ((c = f.read()) == '=')
                  System.out.print(".eq.");
               else {
                  System.out.print("<-");
                  f.unread(c);
               }
               break;
            default:
               System.out.print((char) c);
               break;
            }
         }
      } catch (IOException e) {
         System.out.println("I/O Error: " + e);
      }
   }
}



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