Java PushbackInputStream Example

/*
	Java PushbackInputStream Example
	This example shows how to use Java PushbackInputStream class provided in 
	java.io package.
 
*/
 
import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.PushbackInputStream;
 
public class JavaPushbackInputStreamExamples {
 
	public static void main(String[] args) {
 
		//example expression you want to evaluate in your program 
		String strExpression = "a = a++ + b;";
 
		/*
		 * Here, while, evaluating the expression, You need to know
		 * whether it is ++ operator or + plus operator. Basically,
		 * you need to read ahead or peek whether another + follows 
		 * immediately after one + sign.
		 */
 
		 //get bytes from the expression string
		 byte bytes[] = strExpression.getBytes();
 
		 //create stream from expression bytes
		ByteArrayInputStream bis = new ByteArrayInputStream(bytes);
 
		/*
		 * PushbackInputStream provides below given two constructors.
		 * 
		 * 1) PushbackInputStream(InputStream is)
		 * creates PushbackInputStream from provided InputStream object
		 * 
		 * 2)PushbackInputStream(InputStream is, int size)
		 * Creates PushbackInputStream from specified InputStream object
		 * with pushback buffer of specified size.
		 */
		//create PushbackInputStream from ByteArrayInputStream
		PushbackInputStream pis = new PushbackInputStream(bis);
 
		int ch;
 
		try
		{
 
			while( (ch = pis.read())!= -1)
			{
				//we encountered first + operator
				if(ch == '+')
				{
					//peek to see if another + follows
					if( (ch = pis.read()) == '+')
					{
						System.out.print("Plus Plus");
					}
					else
					{
						//push back one position as we did not get another +
						pis.unread(ch);
 
						System.out.print("+");
					}
				}
				else
				{
					//print the character
					System.out.print((char)ch);
				}
			}
		}
		catch(IOException ioe)
		{
			System.out.println("Exception while reading" + ioe);
		}
	}
}
 
/*
Output of this program would be,
a = aPlus Plus + b;
*/