Programming Forums > Application Development > Java

ReggaetonKing · May 4th, 2006, 11:53 PM

I am now touching on Java I/O Files and Stream classes. I have read 3 different books on I/O classes in Java. All of these books are so consistent up to the subject of files and streams.

Does anyone have any good advice for making files and streams a lot easier to learn and comprehend. Or maybe another book which taught you Java's Files and Stream classes well.

I don't know if it's me or the books (I know it's me...) but I just don't seem to get this subject.

jaeusm · May 6th, 2006, 12:12 AM

What, exactly, is giving you problems?

ReggaetonKing · May 6th, 2006, 12:37 AM

The whole I/O classes. Just an easier way to learn how to open files, save files, and read files, and use file data for my programs.

jaeusm · May 6th, 2006, 1:57 AM

Conceptually, you can think of streams as the medium over which data is transmitted between two "things" -- in this case, your program and a file. In other words, you need to:
1. Create a stream for either input or output,
2. Connect one end to your program,
3. Connect the other end to a file.

These steps are only conceptual, as you can achieve all this in one line of code. For instance, in order to write data to file, you might use a PrintWriter object:

(Toggle Plain Text)

PrintWriter pw = new PrintWriter(new File("filename.txt"));

Now you can use the PrintWriter methods to write text to the file named "filename.txt":

(Toggle Plain Text)

pw.println("This is my file");
pw.flush();

When you are finished using the stream, be sure to close it:

(Toggle Plain Text)

pw.close();

Similarly, you can create a stream for reading data from a file. For instance, you might want to read in a line of text from a text file using a BufferedReader object:

(Toggle Plain Text)

BufferedReader br = new BufferedReader(new FileReader(new File("filename.txt")));
String line = br.readLine();

As mentioned above, when you are finished with the stream, make sure you close it.

There are several different stream classes you can choose from. BufferedReader is a good choice when working with text files. If you were working with files that did not contain readable text, another stream class such as InputStream might be a good choice. Each of the stream classes have their strengths, weaknesses, and applications.

ReggaetonKing · May 6th, 2006, 8:51 AM

How would I be able to retreive objects and the data that I created in my program from a file. Say example, I have a 2 textfields and the user put his phone number in one and last name in another, how would I be able to retreive the data from which a user entered in and have it exactly how it was.

Arevos · May 6th, 2006, 11:03 AM

You can use an ObjectOutputStream object to save objects that can be serialized. An object needs to first implement the Serializable interface in order to be serialized (most basic Java types do by default).

(Toggle Plain Text)

// Open an output stream to a file
OutputStream outputStream = new FileOutputStream("filename.txt");

// Layer an ObjectOutputStream on top of the FileOutputStream
ObjectOutputStream objectOutput = new ObjectOutputStream(outputStream);

// Save an object
objectOutput.writeObject("An object, in this case, a normal String");

// Close the stream
objectOutput.close();

// Open an input stream to a file
InputStream inputStream = new FileInputStream("filename.txt");

// Layer an ObjectInputStream on top of the FileInputStream
ObjectInputStream objectInput = new ObjectInputStream(inputStream);

// Load an object
String myMessage = (String)objectInput.readObject();

// Close the stream
objectInput.close();

Arevos · May 6th, 2006, 11:14 AM

As an aside, Java streams make quite a bit of sense after a while of using them. A stream in Java is a way to output a series of bytes, or to receive a series of bytes as input. This is a very low level approach, and normally programmers don't directly access streams. Often, functionality is layered on top of these streams with extra classes.

For instance, the PrintWriter object allows you to send strings directly into the stream using the print and println methods. System.out is itself a PrintWriter object. Another example is the ObjectOutputStream shown above. This object allows a user to send objects across a stream.

And it's not just files that use streams. Any continuous data connection in Java does including TCP connections over the Internet.

May 4th, 2006, 11:53 PM	#1
ReggaetonKing Sexy Programmer Join Date: Nov 2005 Location: New Jersey Posts: 891 Rep Power: 4	Java's I/O Files and Streams I am now touching on Java I/O Files and Stream classes. I have read 3 different books on I/O classes in Java. All of these books are so consistent up to the subject of files and streams. Does anyone have any good advice for making files and streams a lot easier to learn and comprehend. Or maybe another book which taught you Java's Files and Stream classes well. I don't know if it's me or the books (I know it's me...) but I just don't seem to get this subject. __________________ I would love to change the world, but they won't give me the source code!

May 6th, 2006, 12:37 AM	#3
ReggaetonKing Sexy Programmer Join Date: Nov 2005 Location: New Jersey Posts: 891 Rep Power: 4	The whole I/O classes. Just an easier way to learn how to open files, save files, and read files, and use file data for my programs. __________________ I would love to change the world, but they won't give me the source code!

May 6th, 2006, 1:57 AM	#4
jaeusm Programmer Join Date: Feb 2006 Location: Columbus, OH Posts: 84 Rep Power: 3	Conceptually, you can think of streams as the medium over which data is transmitted between two "things" -- in this case, your program and a file. In other words, you need to: 1. Create a stream for either input or output, 2. Connect one end to your program, 3. Connect the other end to a file. These steps are only conceptual, as you can achieve all this in one line of code. For instance, in order to write data to file, you might use a PrintWriter object: (Toggle Plain Text) PrintWriter pw = new PrintWriter(new File("filename.txt")); PrintWriter pw = new PrintWriter(new File("filename.txt")); Now you can use the PrintWriter methods to write text to the file named "filename.txt": (Toggle Plain Text) pw.println("This is my file"); pw.flush(); pw.println("This is my file"); pw.flush(); When you are finished using the stream, be sure to close it: (Toggle Plain Text) pw.close(); pw.close(); Similarly, you can create a stream for reading data from a file. For instance, you might want to read in a line of text from a text file using a BufferedReader object: (Toggle Plain Text) BufferedReader br = new BufferedReader(new FileReader(new File("filename.txt"))); String line = br.readLine(); BufferedReader br = new BufferedReader(new FileReader(new File("filename.txt"))); String line = br.readLine(); As mentioned above, when you are finished with the stream, make sure you close it. There are several different stream classes you can choose from. BufferedReader is a good choice when working with text files. If you were working with files that did not contain readable text, another stream class such as InputStream might be a good choice. Each of the stream classes have their strengths, weaknesses, and applications.

May 6th, 2006, 8:51 AM	#5
ReggaetonKing Sexy Programmer Join Date: Nov 2005 Location: New Jersey Posts: 891 Rep Power: 4	How would I be able to retreive objects and the data that I created in my program from a file. Say example, I have a 2 textfields and the user put his phone number in one and last name in another, how would I be able to retreive the data from which a user entered in and have it exactly how it was. __________________ I would love to change the world, but they won't give me the source code!

May 6th, 2006, 11:03 AM	#6
Arevos Programming Guru Join Date: Aug 2005 Location: England Posts: 1,499 Rep Power: 5	You can use an ObjectOutputStream object to save objects that can be serialized. An object needs to first implement the Serializable interface in order to be serialized (most basic Java types do by default). (Toggle Plain Text) // Open an output stream to a file OutputStream outputStream = new FileOutputStream("filename.txt"); // Layer an ObjectOutputStream on top of the FileOutputStream ObjectOutputStream objectOutput = new ObjectOutputStream(outputStream); // Save an object objectOutput.writeObject("An object, in this case, a normal String"); // Close the stream objectOutput.close(); // Open an input stream to a file InputStream inputStream = new FileInputStream("filename.txt"); // Layer an ObjectInputStream on top of the FileInputStream ObjectInputStream objectInput = new ObjectInputStream(inputStream); // Load an object String myMessage = (String)objectInput.readObject(); // Close the stream objectInput.close(); // Open an output stream to a file OutputStream outputStream = new FileOutputStream("filename.txt"); // Layer an ObjectOutputStream on top of the FileOutputStream ObjectOutputStream objectOutput = new ObjectOutputStream(outputStream); // Save an object objectOutput.writeObject("An object, in this case, a normal String"); // Close the stream objectOutput.close(); // Open an input stream to a file InputStream inputStream = new FileInputStream("filename.txt"); // Layer an ObjectInputStream on top of the FileInputStream ObjectInputStream objectInput = new ObjectInputStream(inputStream); // Load an object String myMessage = (String)objectInput.readObject(); // Close the stream objectInput.close();

May 6th, 2006, 12:12 AM	#2
jaeusm Programmer Join Date: Feb 2006 Location: Columbus, OH Posts: 84 Rep Power: 3	What, exactly, is giving you problems?

May 6th, 2006, 11:14 AM	#7
Arevos Programming Guru Join Date: Aug 2005 Location: England Posts: 1,499 Rep Power: 5	As an aside, Java streams make quite a bit of sense after a while of using them. A stream in Java is a way to output a series of bytes, or to receive a series of bytes as input. This is a very low level approach, and normally programmers don't directly access streams. Often, functionality is layered on top of these streams with extra classes. For instance, the PrintWriter object allows you to send strings directly into the stream using the print and println methods. System.out is itself a PrintWriter object. Another example is the ObjectOutputStream shown above. This object allows a user to send objects across a stream. And it's not just files that use streams. Any continuous data connection in Java does including TCP connections over the Internet.

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Programming Forums > Application Development > Java

Java's I/O Files and Streams