*Something.java[2] means the file "Something.java" at line 2.

Include files

In C++ if we are going to read and write with files we need to include <iostream> at Main.cpp[1] and <fstream> at Main.cpp[2].

Opening a file for output

In Java there are three steps needed to open a file for writing: 1) specifying the file name and output stream, 2) wrapping the output stream with a PrintStream so that the nice methods are available and 3) catching an exception for any errors. In C++ there is only the opening of the output file and an if statement to catch any errors. In Java we specify the file name ("data.txt") by including it in a FileOutputStream constructor (Main.java[8]). In C++ we use the open() method as at Main.cpp[8]. For text files, Java has the additional step of wrapping the output stream myFile in a PrintStream object called myOutputFile as shown at Main.java[9]. The PrintStream class provides the various print() and println() that we use so often. This wrapping is not required in C++ the ofstream class provides all of the << operators needed for writting out text.

If there is an error in opening a file, Java with raise an exception. This must be caught in order to handle the error. This is done with the try at Main.java[7] and the catch at Main.java[15-16]. Java's exception mechanism is more powerful but for cases like this the C++ error mechanism is simpler. An ofstream value can be used as a boolean in an if statement. If there has been an error it will return false. Thus the try/catch in Java is replaced by an if statement as shown at Main.cpp[9, 15-16].

Writing to a file

In Java we use print() and println() to write to an output PrintStream as shown at Main.java[10-12]. In C++ we use the << operator just as with cout to write information to an output stream. This is shown at Main.cpp[10-12];

Closing a file

It is very important to close an output file when we are done to ensure that all characters have been written to the file and not stuck in a buffer. This is the same in Java at Main.java[13] as it is in C++ at Main.cpp[13].

Opening a file for input

Each language works similarly on input as it does on output. In Java we specify the file name in a FileInputStream constructor, shown at Main.java[19]. We then wrap it in a Scanner as shown at Main.java[20]. In C++ we use an ifstream for an input file and specify the file name using the open() method as shown at Main.cpp[18-19]. Java uses a try/catch for its file errors (Main.java[17,31-32]). C++ uses the if statements in the same fashion as output files (Main.cpp[23,32-33]).

Checking for end of file

In Java we check for the end of a Scanner stream using the method hasNext() as shown at Main.java[24]. In C++ this function is performed by the >> operator which returns false if it fails to read an input, as shown at Main.cpp[25]. Reading actual values in Java is performed using the Scanner's various next----() methods as at Main.java[25-26]. In C++ we use the >> operator as shown at Main.cpp[25-26].