The DataOutputStream class | Managing Input/Output Files in Java

The DataOutputStream class

• Is part of the java.io package

• Is an extension of the FilterOutputStream class (a superclass that facilitates the chaining of high-level and low-level output streams)

• Is a high-level class that can be used to send primitive values and UTF (“Unicode Transformation Format”) strings to a stream

• Has a single constructor that “chains” to an object that descends from the OutputStream class (such as a FileOutputStream object). For example, if fd is the reference of a File object

DataOutputStream out = new DataOutputStream(new FileOutputStream(fd));

It will construct a DataOutputStream object chained to a FileOutputStream object for sending primitive values and UTF strings to the file. Because a checked, IOException may occur, the statement should be enclosed in a try block with an appropriate catch.

• Has many useful methods as follows:

Because a checked, IOException may occur, calls to these methods should be enclosed in a try block with an appropriate catch. Consult the Java API documentation for more details.

• Example. The following program can be used to create a file of double values on disk.

import java.io.*;
public class App
{
public static void main(String[] args)
{

// Local variables and object references.

char again = ‘y’;
File fd;
DataOutputStream out;

// Get the path name from the user.

System.out.print(“Enter the file’s complete path name: “);
fd = new File(Keyboard.readString());

// Try to write data to the output stream.

try
{

// Open an output stream for the file.

out = new DataOutputStream(new FileOutputStream(fd));

// This loop asks the user to enter a number and writes it to the
// stream. The user is then asked if they want to enter another.

while (again == ‘Y’ || again == ‘y’) {
System.out.print(“Enter any real number (n.n): “);
double theNumber = Keyboard.readDouble();
out.writeDouble(theNumber);
System.out.print(“Again? (Y/N): “);
again = Keyboard.readChar();
}

// Close the stream.

out.close();
System.out.println(“Closed – ” + fd.getPath());
}

// Catch an IOException if one is thrown.

catch (IOException e)
{
System.out.println(e.getMessage());
}
}
}