FileOutputStream class

java.lang.Object
 |
 +-java.io.OutputStream
    |
    +-java.io.FileOutputStream

FileOutputStream creates an OutputStream that you can use to write bytes to a file.

Its most commonly used constructors are shown here:

FileOutputStream(String filePath)

filePath is the full path name of a file

FileOutputStream(File fileObj)

fileObj is a File object that describes the file.

FileOutputStream(String filePath, boolean append)

filePath is the full path name of a file

FileOutputStream(File fileObj, boolean append)

fileObj is a File object that describes the file.

If append is true, the file is opened in append mode.

Creation of a FileOutputStream is not dependent on the file already existing. FileOutputStream will create the file before opening it for output when you create the object.

Opening a read-only file will throw an IOException.

 
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;

public class Main {
  public static void main(String args[]) throws IOException {
    byte buf[] = "this is a test".getBytes();
    OutputStream f0 = new FileOutputStream("file1.txt");
    for (int i = 0; i < buf.length; i += 2) {
      f0.write(buf[i]);
    }
    f0.close();
    OutputStream f1 = new FileOutputStream("file2.txt");
    f1.write(buf);
    f1.close();
    OutputStream f2 = new FileOutputStream("file3.txt");
    f2.write(buf, buf.length - buf.length / 4, buf.length / 4);
    f2.close();
  }
}
  

Methods from FileOutputStream

void close()

Closes this file output stream and releases any system resources associated with this stream.

FileChannel getChannel()

Returns the unique FileChannel object associated with this file output stream.

FileDescriptor getFD()

Returns the file descriptor associated with this stream.

void write(byte[] b)

Writes b.length bytes from the specified byte array to this file output stream.

void write(byte[] b, int off, int len)

Writes len bytes from the specified byte array starting at offset off to this file output stream.

void write(int b)

Writes the specified byte to this file output stream.

Revised from Open JDK source code

Create FileOutputStream object from File object

import java.io.File;
import java.io.FileOutputStream;

public class Main {
  public static void main(String[] args) throws Exception {
    File file = new File("C:/demo.txt");
    FileOutputStream fos = new FileOutputStream(file);
  }
}

Write file using FileOutputStream

import java.io.FileOutputStream;

public class Main {

  public static void main(String[] args) throws Exception {
    FileOutputStream fos = new FileOutputStream("C:/demo.txt");

    byte b = 01;
    fos.write(b);
    fos.close();
  }
}