DataInputStream and DataOutputStream for primitive data

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

If we want to read-write primitive data types (such as int, float, etc.) then 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 types.

1 DataInputStream Class

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

DataInputStream is a subtype 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: dataOutputStream in java Example

import java.io.DataOutputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;

public class DataOutputStreamExample {

    public static void main(String[] s) throws FileNotFoundException, IOException {
        FileOutputStream fos = new FileOutputStream("D:/item.txt"); //Open file “item” for write
        DataOutputStream dos = new DataOutputStream(fos);
        String itemName = "Laptop";

        dos.writeUTF(itemName);
        int quantity = 500;
        dos.writeInt(quantity);
        double price = 70000;
        dos.writeDouble(price);
        System.out.println("Record saved successfully");
        dos.close();
        fos.close();
    }
}

Example: dataInputStream java example

package com.sspu.javatestproject;

import java.io.DataInputStream;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;


public class DataInputStreamExample {

    public static void main(String[] args) throws FileNotFoundException, IOException {
        FileInputStream fis = new FileInputStream("D:/item.txt"); //open file a for read
        DataInputStream dis = new DataInputStream(fis);
        System.out.println("Item Details are");
        System.out.println("Item Name " + dis.readUTF());
        System.out.println("quantity " + dis.readInt());
        System.out.println("price " + dis.readDouble());

        dis.close();
        fis.close();
    }
}

name Ram Kumar
Item Details are
Item Name Laptop
quantity 500
price 70000.0

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

Here we discussed DataInputStream and DataOutputStream to read file data.

import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;

public class JavaTestProject {

    public static void main(String args[]) throws IOException {
        FileOutputStream fos = new FileOutputStream("D:/a.txt"); //Open file “a” for write
        DataOutputStream dos = new DataOutputStream(fos);
        //write primitive data on file A
        String name = "Ram Kumar";
        dos.writeUTF(name);
        int age = 19;
        dos.writeInt(age);
        double salary = 130000d;
        dos.writeDouble(salary);
        boolean preference = false;
        dos.writeBoolean(preference);
        char gender = 'M';
        dos.writeChar(gender);
        dos.close();
        fos.close();
        //read primitive data from file A
        FileInputStream fis = new FileInputStream("D:/a.txt"); //open file a for read
        DataInputStream dis = new DataInputStream(fis);
        System.out.println("name " + dis.readUTF());
        System.out.println("age " + dis.readInt());
        System.out.println("salary " + dis.readDouble());
        System.out.println("preference " + dis.readBoolean());
        System.out.println("gender " + dis.readChar());
        dis.close();
        fis.close();
    }
}

Output

name Ram Kumar
age 19
salary 130000.0
preference false
gender M

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