import java.io.IOException; import java.io.RandomAccessFile; public class TextMangler { public static void swapAsAndOs(RandomAccessFile file) throws IOException { long pos = 0; while (pos < file.length()) { char c = (char) file.read(); char replacement = 0; if (c == 'a') replacement = 'o'; if (c == 'A') replacement = 'O'; else if (c == 'o') replacement = 'a'; else if (c == 'O') replacement = 'A'; if (replacement != 0) { file.seek(pos); file.write((byte) replacement); } pos++; } } // this method checks your work public static void main(String[] args) throws IOException { RandomAccessFile file = new RandomAccessFile("data.txt", "rw"); swapAsAndOs(file); file.close(); } }