Managing Input/Output Files in Java

The DataInputStream class

. Is part of the java.io package

. Is an extension of the FilterInputStream class (a superclass that facilitates the chaining of high-level and low-level input streams)

. Is a high-level class that can be used to read primitive values and UTF ("Unicode Transformation Format") strings from a stream

. Has a single constructor that "chains" to an object that descends from the InputStream class (such as a FileInputStream object). For example, if fd is the reference of a File object

DataInputStream in = new DataInputStream(new FileInputStream(fd));

It will construct a DataInputStream object chained to a FileInputStream object for reading primitive values and UTF strings from 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 read a file of double values from disk. It can be used to display the values stored by the previous sample program.

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

// Local variables and object references.

File fd;
DataInputStream in;

// Get the path name from the user.

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

// Try to read data from the input stream.

try {

// Open an input stream for the file.

in = new DataInputStream(new FileInputStream(fd));

// This loop reads a double value from the stream and displays
// it. The loop ends when end of file is reached.

try
{
while (true)
{
System.out.println(in.readDouble());
}
}
catch (EOFException e)
{
System.out.println("");
}

// Close the stream.

in.close();
System.out.println("Closed - " + fd.getPath());
}

// Catch an IOException if one is thrown.

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