Enhance the performance of the source code in Java
Exceptions used for control flow


inputFile = new File(args[0]);



Using exceptions for the control flow in your program is harmful for the speed of executing. When making a exception, much of the time is spent on constructing the stack trace.

if (args.length == 0) {
    System.out.println("Usage: java -jar program.jar &lt;filename&gt;");
    return;
}


Using unbuffered IO


FileReader reader = new FileReader(inputFile);
while((read = reader.read(charBuffer)) != -1) {



You are using unbuffered IO, this means for every call to the read() method, a call will be dispatched to the underlying file system to read 1 byte. Wrapping the FileReader in a BufferedReader increases the performance, and gives you access to prebuild methods such as nextLine

BufferedReader reader = new BufferedReader(new FileReader(inputFile));


You are trying to reimplement the wheel with your loop


while((read = reader.read(charBuffer)) != -1) {
        for (int i = 0; i &lt; read; ++i) {
            char c = charBuffer[i];
            if (c == '\r' || c == '\n') {
                if (token.length() != 0) {
                    // read date
 ...
                }
            }
            else if (c == ' ') {
                // flush token
                if (tokenIndex == 0) {
                    // read name
                    name = token;
                    token = "";
                    tokenIndex++;
                }
                else if (tokenIndex == 1) {
                    // read amount
                    amount = token;
                    token = "";
                    tokenIndex++;
                }
            }
            else token = token + c;
        }



The above code is pretty inefficient duo to the large amount of stringbuilder and string object created, a better way is reading a whole line using BufferedReader.readLine() and splitting that on spaces:

String line;
while((line = reader.readLine()) != null) {
    int firstSpace = line.indexOf(' ');
    int secondSpace = line.indexOf(' ', firstSpace + 1);

    String name = line.subString(0, firstSpace);
    String amount = line.subString(firstSpace + 1, secondSpace);
    String date = line.subString(secondSpace + 1, line.length());

    year = Integer.parseInt(date.substring(0, 4));
    ...
} 


This also decreases the size of the actual code

Don't declare variables until you actually need them

File inputFile;
...
int read;
String token = "";
...
String name = null;
int year = -1;
int month = -1;
int day = -1;
String amount = null;


While the performance impact of this isn't that high, it makes your code look better when seeing the variables declared on the point where it is used.

Not closing your IO streams

CLosing your IO streams is important to prevent the java program from getting errors for too many open files, closing can be done by calling reader.close(), or by using a try-with-resources block.

Fixed code

After applying all the steps above, you should get a code similar to the following:


public static void main(String[] args) throws IOException {
    if (args.length == 0) {
        System.out.println("Usage: java -jar program.jar &lt;filename&gt;");
        return;
    }

    File inputFile = new File(args[0]);
    long start = System.currentTimeMillis();

    try (BufferedReader reader = new BufferedReader(new FileReader(inputFile))) {
        String line;
        while((line = reader.readLine()) != null) {
            int firstSpace = line.indexOf(' ');
            int secondSpace = line.indexOf(' ', firstSpace + 1);

            String name = line.subString(0, firstSpace);
            String amount = line.subString(firstSpace + 1, secondSpace);
            String date = line.subString(secondSpace + 1, line.length());

            int year = Integer.parseInt(date.substring(0, 4));
            int month = Integer.parseInt(date.substring(5, 7));
            int day = Integer.parseInt(date.substring(8, 10));

            // flush line
            System.out.print(name.toUpperCase());
            System.out.print(" ");
            System.out.print(amount.indexOf('.') == -1 ? true : false);
            System.out.print(" ");
            System.out.print(day &lt; 10 ? "0" + day : day);
            System.out.print("/");
            System.out.print(month &lt; 10 ? "0" + month : month);
            System.out.print("/");
            System.out.print(year);
            System.out.println();
        } 
    }
    System.out.println ("Time taken for String in if/else if :"+ (System.currentTimeMillis() - start));
}