DataInputStream Class

Package: java.io

This class reads primitive data types, such as integers and doubles, directly from an input stream. It is the class you’ll use most often to read data from a binary file.

The DataInputStream class is one of many Java I/O classes that use streams. For more information, see Streams (Overview).

Constructor

Constructor	Description
DataInputStream (InputStream in)	Creates a data input stream from any object that extends the InputStream class. Typically, you pass this constructor a BufferedInputStream object.

Methods

Method	Description
boolean readBoolean()	Reads a boolean value from the input stream. It throws EOFException and IOException.
byte readByte()	Reads a byte value from the input stream. It throws EOFException and IOException.
char readChar()	Reads a char value from the input stream. It throws EOFException and IOException.
double readDouble()	Reads a double value from the input stream. It throws EOFException and IOException.
float readFloat()	Reads a float value from the input stream. It throws EOFException and IOException.
int readInt()	Reads an int value from the input stream. It throws EOFException and IOException.
long readLong()	Reads a long value from the input stream. It throws EOFException and IOException.
short readShort()	Reads a short value from the input stream. It throws EOFException and IOException.
String readUTF()	Reads a string stored in UTF format from the input stream. It throws EOFException, IOException, and UTFDataFormat Exception. (UTF is a common format for storing string data using two bytes to represent each character.)

Creating a DataInputStream

To read data from a binary file, you want to connect a DataInputStream object to an input file. To do that, you use a File object to represent the file, a FileInputStream object that represents the file as an input stream, a BufferedInputStream object that adds buffering to the mix, and finally a DataInputStream object to provide the methods that read various data types. Here’s an example:

File file;

FileInputStream fstream;

BufferedInputStream bstream;

DataInputStream in;

file = new File(“movies.dat”);

fstream = new FileInputStream(file);

bstream = new BufferedInputStream(fs);

in = new DataInputStream(bs);

Reading from a data input stream

To read data from a binary file, you use the various read methods of the DataInputStream class to read the fields one at a time. Of course, to do that, you must know the exact sequence in which data values appear in the file.

Suppose a file includes information from a video store rental database that represents the title of a movie as a string, the year the movie was made as an integer, and the movie’s rental price as a double, in that order. To read these three values, you’d use these statements:

String title = in.readUTF();

int year = in.readInt();

double price = in.readDouble();

The read methods usually are used in a while loop to read all the data from the file. When the end of the file is reached, EOFException is thrown. Then you can catch this exception and stop the loop. For example:

boolean eof = false;

while (!eof)

{

try

{

String title = in.readUTF();

int year = in.readInt();

double price = in.readDouble();

// do something with the data here

}

catch (EOFException e)

{

eof = true;

}

catch (IOException e)

{

System.out.println(“An I/O error “

+ “has occurred!”);

System.exit(0);

}

}

Here, the boolean variable eof is set to true when EOFException is thrown, and the loop continues to execute as long as eof is false.

After the entire file has been read, you can close the stream by calling the close method, like this:

in.close();

This method also throws IOException, so you want to place it inside a try/catch block. (See try Statement in Part 2 for more information.)