FileOutputStream

FileOutputStream class is a subclass of OuputStream abstract class. FileOutputStream is used create an output stream, which is used to write byte/bytes to a file.

Constructors :

1) FileOutputStream(File file)
This constructor creates a FileOutputStream object to write to a file specified by the File object, which is passed to this constructor as a parameter. Example: `File file= new File("D:\\Textbook.txt"); FileInputStream fis= new FileInputStream(file);`

2) FileOutputStream(String path)
This constructor creates a FileOutputStream to write to a file which is accessed by the path mentioned in the parameters of this constructor. Example: `FileOutputStream fis= new FileOutputStream("D:\\TextBook.txt");`

In both of the examples of different constructors, we have created a FileOutputStream object to create an output stream to write to a file called "TextBook.txt" which is located in the D: drive.

Methods for writing using FileOutputStream

Some methods that we generally use while working with FileOutputStream are shown in the table below:

Methods	Description
flush()	This method flushes any buffered data to be written out of this output stream.
write(int b)	This method writes one byte at a time to this output stream.
write(byte[])	This method writes a whole byte array at a time to this input stream.
close()	This method closes this outut stream and also frees any resources connected with this output stream.

Writing one byte at a time to a file using write() method of FileOutputStream.

In the upcoming example, we are going to write a byte at a time to a file called TextBook.txt, by passing its full path D:\\TextBook.txt to the constructor of FileOutputStream. To do this, first the file is created and then bytes(one byte at a time) is written to it.

// Java - A program to write one byte at a time to a file using FileOutputStream. 


import java.io.*;

class A
{
public static void main(String... ar)
{
	try
	{
		String str= new String("World peace is extremely important");
		byte bA[]=str.getBytes();

		FileOutputStream fos=new FileOutputStream("D:\\TextBook.txt");
		for(byte byt:bA)
		{
			fos.write(byt);	//writing one byte at a time to the file.
		}
		fos.flush();
		fos.close();
	}
	catch(IOException e)
	{
		System.out.println(e);
	}
}
}

Output is -:

After the execution of the program, a file called "TextBook.txt" is created in D: drive, with the contents:
World peace is extremely important.

Program Analysis

A byte array, bA, is initialized from a String- "World peace is extremely important".
Using a for-each loop, one byte at a time is written out of the byte array(bA) to the file TextBook.txt, by calling the write() method of FileOutputStream.
The flush() method is called to flush any buffered bytes out of FileOutputStream to the file TextBook.txt.
Finally, the stream is closed by calling the close() method on the FileObjectStream's object, to free the resources still connected to this stream.

Writing a byte array to a file using write(byte[] b) method of FileOutputStream.

In the next example, we are going to write a whole byte array(all at once) to a file with its full path- D:\\Book1.txt. This performs faster writing, because writing a whole byte array at once is faster than writing one byte at a time.

//Java - A program to write a byte array to a File using FileOutputStream. 

import java.io.*;

class A
{
public static void main(String... ar)
{
	try
	{
		String str=new String("World peace is extremely important");
		byte bA[]=str.getBytes();

		FileOutputStream fos=new FileOutputStream("D:\\Book1.txt");
		fos.write(bA);

		fos.flush();
		fos.close();
	}
	catch(IOException e)
	{
		System.out.println(e);
	}
}
}

Output is -:

After the execution of this program, a file called "Book1.txt" is created in D: drive, with the contents -:
World peace is extremely important.

Program Analysis

The program writes a byte array, bA(all at once) to the file Book1.txt, by calling the write(byte[] b) method of FileOutputStream class.

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