CSC108 Lecture #4 Example

TestReverse.java - Version 1

/**
 * TestReverse: This program takes input from the user, and
 *    prints out the reverse of each line of input.  The program
 *    stops when the user enters "quit"
 */
import java.io.*;
public class TestReverse {
	public static void main (String[] args) throws IOException {

		BufferedReader getit;
		getit = new BufferedReader
			  (new InputStreamReader (System.in));

		// Prompt user to enter text.
		System.out.println ("Enter lines of text.");
		System.out.println ("Type quit to stop.");
		System.out.flush ();

		// Read first line before loop.
		String text = getit.readLine();
		
		// Loop until the user enters quit
		while (true) {

			// Leave loop if word was quit
			if (text.equals("quit"))
				break;

			// Print out reverse of word
			System.out.println (reverse(text));

			// Read next line of text
			text = getit.readLine();
		}
		System.out.println ("End of program.");
	}
	
	/*
         * reverse: return value is same as parameter "original"
         *          reversed.
         */
	public static String reverse (String original) {

		String reversed = ""; 	// where we build the
					// reversed string

		// where are we in original?
		int pos = original.length() - 1;

		// for each character ...
		while (pos >= 0) {
			// "write it down"
			reversed = reversed + original.charAt(pos);
			pos -= 1;  // more of "for each character"
		}
		return reversed;
	}

}

TestReverse2.java - Version 2

In this version, we have moved the readLine() into the loop, and have eliminated the call to readline() at the end of the loop.

/**
 * TestReverse2: This program takes input from the user, and
 *    prints out the reverse of each line of input.  The program
 *    stops when the user enters "quit"
 */
import java.io.*;
public class TestReverse2 {
	public static void main (String[] args) throws IOException {

		BufferedReader getit;
		getit = new BufferedReader
			  (new InputStreamReader (System.in));

		// Prompt user to enter text.
		System.out.println ("Enter lines of text.");
		System.out.println ("Type quit to stop.");
		System.out.flush ();

		// Loop until the user enters quit
		while (true) {
			// Read a line of text
			String text = getit.readLine();

			// Leave loop if word was quit
			if (text.equals("quit"))
				break;

			// Print out reverse of word
			System.out.println (reverse(text));
		}
		System.out.println ("End of program.");
	}
	
	/*
         * reverse: return value is same as parameter "original"
         *          reversed.
         */
	public static String reverse (String original) {

		String reversed = ""; 	// where we build the
					// reversed string

		// where are we in original?
		int pos = original.length() - 1;

		// for each character ...
		while (pos >= 0) {
			// "write it down"
			reversed = reversed + original.charAt(pos);
			pos -= 1;  // more of "for each character"
		}
		return reversed;
	}

}

Output - same for both versions

Enter lines of text.
Type quit to stop.
Hello
olleH
Montreal
laertnoM
See you later!
!retal uoy eeS
 quit
tiuq
quit
End of program.