DataInputStream and DataOutputStream for primitive data

In java, basic input-output stream provides a method for reading & writing bytes or character in a file.

If we want to read-write primitive data typa (such as int , float etc.) than we can use filter classes to filter data in the original stream.

DataInputStream & DataOutputStream are two filter classes used for creating “data streams” for handling primitive data type.

1 DataInputStream Class

In java DataInputStream class is used to allow application to read primitive data from different sources.

DataInputStream is a sub type of FilterInputStream.

A. DataInputStream Constructor

Sr No	Constructor
1	DataInputStream(InputStream in) Take InputStream object to create DataInputStream

Constructor call of DataInputStream

FileInputStream i = new FileInputStream("A.txt"); //open file A for read DataInputStream I = new DataInputStream(i);

B Methods in DataInputStream

Following are the methods of DataInputStream

Sr No	Method
1	public final int read(byte[] b) throws IOException Reads number of bytes from input stream and store in buffered array b
2	public final int read(byte[] b, int off, int len) throws IOException Reads up to len bytes from input stream and store in buffered array b
3	public final boolean readBoolean() throws IOException Reads one input byte and return true if byte is non zero, else false
4	public final byte readByte() throws IOException Reads and return one input byte
5	public final char readChar() throws IOException Reads two input byte and return a char
6	public final double readDouble() throws IOException Reads eight input byte and return a double value
7	public final float readFloat() throws IOException Reads four input bytes and return a float value
8	public final void readFully(byte[] b) throws IOException Reads some bytes from input stream and store in buffer array b
9	public final int readInt() throws IOException Reads four input bytes and return a integer value
10	public final long readLong() throws IOException Reads eight input bytes and returns a long value
11	public final short readShort() throws IOException Reads one input bytes and returns a short value
12	public final int readUnsignedByte() throws IOException Reads two byte and return unsigned byte value
13	public final String readUTF() throws IOException Reads a string that has been encoded in modified utf-8 format
15	public static final String readUTF(DataInput in) throws IOException Reads from a stream that has been encoded in modified utf-8 format
16	public final int skipBytes(int n) throws IOException Makes attempt to skip n bytes of data from input stream

Example: Write a program to write & read a primitive data on a same file.

import java.io.*;
public class PrimitiveReadWrite {
    public static void main(String args[]) throws IOException {
        FileOutputStream o = new FileOutputStream("A.txt"); //Open file “A” for write
        DataOutputStream O = new DataOutputStream(o);
        //write primitive data on file A
        O.writeInt(1999);
        O.writeDouble(333.89);
        O.writeBoolean(false);
        O.writeChar('X');
        O.close();
        o.close();
        //read primitive data from file A
        FileInputStream i = new FileInputStream("A.txt"); //open file A for read
        DataInputStream I = new DataInputStream(i);
        System.out.println(I.readInt());
        System.out.println(I.readDouble());
        System.out.println(I.readBoolean());
        System.out.println(I.readChar());
        I.close();
        i.close();
    }
}

import java.io.*;

public class PrimitiveReadWrite {

public static void main(String args[]) throws IOException {

FileOutputStream o = new FileOutputStream("A.txt"); //Open file “A” for write

DataOutputStream O = new DataOutputStream(o);

//write primitive data on file A

O.writeInt(1999);

O.writeDouble(333.89);

O.writeBoolean(false);

O.writeChar('X');

O.close();

o.close();

//read primitive data from file A

FileInputStream i = new FileInputStream("A.txt"); //open file A for read

DataInputStream I = new DataInputStream(i);

System.out.println(I.readInt());

System.out.println(I.readDouble());

System.out.println(I.readBoolean());

System.out.println(I.readChar());

I.close();

i.close();

}

Output:

1999

333.89

false