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Java - Streams, Files and I/O


The java.io package contains nearly every class you might ever need to perform input and output (I/O) in Java. All these streams represent an input source and an output destination. The stream in the java.io package supports many data such as primitives, Object, localized characters, etc.

A stream can be defined as a sequence of data. The InputStream is used to read data from a source and the OutputStream is used for writing data to a destination.

Java provides strong but flexible support for I/O related to Files and networks but this tutorial covers very basic functionality related to streams and I/O. We would see most commonly used example one by one:

Byte Streams

Java byte streams are used to perform input and output of 8-bit bytes. Though there are many classes related to byte streams but the most frequently used classes are , FileInputStream andFileOutputStream. Following is an example which makes use of these two classes to copy an input file into an output file:

import java.io.*;
public class CopyFile {
public static void main(String args[]) throws IOException
{
FileInputStream in = null; FileOutputStream out = null;
try {
in = new FileInputStream("input.txt");
out = new FileOutputStream("output.txt");
int c;
while ((c = in.read()) != -1) { out.write(c);
}
}finally {
if (in != null) { in.close();
}
if (out != null) { out.close();
}
}
}
}

Now let's have a file input.txt with the following content:

This is test for copy file.

As a next step, compile above program and execute it, which will result in creating output.txt file with the same content as we have in input.txt. So let's put above code in CopyFile.java file and do the following:

$javac CopyFile.java
$java CopyFile

Character Streams

Java Byte streams are used to perform input and output of 8-bit bytes, where as Java Characterstreams are used to perform input and output for 16 -bit unicode. Though there are many classes related to character streams but the most frequently used classes are , FileReader and FileWriter.. Though internally FileReader uses FileInputStream and FileWriter uses FileOutputStream but here major difference is that FileReader reads two bytes at a time and FileWriter writes two bytes at a time.

We can re-write above example which makes use of these two classes to copy an input file (having unicode characters) into an output file:

import java.io.*;
public class CopyFile {
public static void main(String args[]) throws IOException
{
FileReader in = null; FileWriter out = null;
try {
in = new FileReader("input.txt");
out = new FileWriter("output.txt");
int c;
while ((c = in.read()) != -1) { out.write(c);
}
}finally {
if (in != null) { in.close();
}
if (out != null) { out.close();
}
}
}
}

Now let's have a file input.txt with the following content:

This is test for copy file.

As a next step, compile above program and execute it, which will result in creating output.txt file with the same content as we have in input.txt. So let's put above code in CopyFile.java file and do the following:

$javac CopyFile.java
$java CopyFile

Standard Streams

All the programming languages provide support for standard I/O where user's program can take input from a keyboard and then produce output on the computer screen. If you are aware if C or C++ programming languages, then you must be aware of three standard devices STDIN, STDOUT and STDERR. Similar way Java provides following three standard streams
  • Standard Input: This is used to feed the data to user's program and usually a keyboard is used as standard input stream and represented as System.in.
  • Standard Output: This is used to output the data produced by the user's program and usually a computer screen is used to standard output stream and represented as System.out.
  • Standard Error: This is used to output the error data produced by the user's program and usually a computer screen is used to standard error stream and represented as System.err.
Following is a simple program which creates InputStreamReader to read standard input stream until the user types a "q":

import java.io.*;
public class ReadConsole {
public static void main(String args[]) throws IOException
{
InputStreamReader cin = null;
try {
cin = new InputStreamReader(System.in);
System.out.println("Enter characters, 'q' to quit.");
char c;
do {
c = (char) cin.read(); System.out.print(c);
} while(c != 'q'); }finally {
if (cin != null) { cin.close();
}
}
}
}

Let's keep above code in ReadConsole.java file and try to compile and execute it as below. This program continues reading and outputting same character until we press 'q':

$javac ReadConsole.java
$java ReadConsole
Enter characters, 'q' to quit.
1
1
e
e
q
q

Reading and Writing Files:

As described earlier, A stream can be defined as a sequence of data. The InputStream is used to read data from a source and the OutputStream is used for writing data to a destination.

Here is a hierarchy of classes to deal with Input and Output streams.

The two important streams are FileInputStream and FileOutputStream, which would be discussed in this tutorial:

FileInputStream:

This stream is used for reading data from the files. Objects can be created using the keyword new and there are several types of constructors available.

Following constructor takes a file name as a string to create an input stream object to read the file.:

InputStream f = new FileInputStream("C:/java/hello");

Following constructor takes a file object to create an input stream object to read the file. First we create a file object using File() method as follows:

File f = new File("C:/java/hello");
InputStream f = new FileInputStream(f);

Once you have InputStream object in hand, then there is a list of helper methods which can be used to read to stream or to do other operations on the stream.
SNMethods with Description
1public void close() throws IOException{}
This method closes the file output stream. Releases any system resources associated with the file. Throws an IOException.
2protected void finalize()throws IOException {}
This method cleans up the connection to the file. Ensures that the close method of this file output stream is called when there are no more references to this stream. Throws an IOException.
3public int read(int r)throws IOException{}
This method reads the specified byte of data from the InputStream. Returns an int. Returns the next byte of data and -1 will be returned if it's end of file.
4public int read(byte[] r) throws IOException{}
This method reads r.length bytes from the input stream into an array. Returns the total number of bytes read. If end of file -1 will be returned.
5public int available() throws IOException{}
Gives the number of bytes that can be read from this file input stream. Returns an int.
There are other important input streams available, for more detail you can refer to the following links:
  • ByteArrayInputStream
  • DataInputStream
ByteArrayInputStream

The ByteArrayInputStream class allows a buffer in the memory to be used as an InputStream. The input source is a byte array. There are following forms of constructors to create ByteArrayInputStream objects

Takes a byte array as the parameter:

ByteArrayInputStream bArray = new ByteArrayInputStream(byte [] a);

Another form takes an array of bytes, and two ints, where off is the first byte to be read and len is the number of bytes to be read.

ByteArrayInputStream bArray = new ByteArrayInputStream(byte []a,
int off,
int len)

Once you have ByteArrayInputStream object in hand then there is a list of helper methods which can be used to read the stream or to do other operations on the stream.
SNMethods with Description
1public int read()
This method reads the next byte of data from the InputStream. Returns an int as the next byte of data. If it is end of file then it returns -1.
2public int read(byte[] r, int off, int len)
This method reads upto len number of bytes starting from off from the input stream into an array. Returns the total number of bytes read. If end of file -1 will be returned.
3public int available()
Gives the number of bytes that can be read from this file input stream. Returns an int that gives the number of bytes to be read.
4public void mark(int read)
This sets the current marked position in the stream. The parameter gives the maximum limit of bytes that can be read before the marked position becomes invalid.
5public long skip(long n)
Skips n number of bytes from the stream. This returns the actual number of bytes skipped.
Example:

Following is the example to demonstrate ByteArrayInputStream and ByteArrayOutputStream

import java.io.*;
public class ByteStreamTest {
public static void main(String args[])throws IOException {
ByteArrayOutputStream bOutput = new ByteArrayOutputStream(12);
while( bOutput.size()!= 10 ) {
// Gets the inputs from the user
bOutput.write(System.in.read());
}
byte b [] = bOutput.toByteArray();
System.out.println("Print the content");
for(int x= 0 ; x < b.length; x++) {
// printing the characters
System.out.print((char)b[x] + " ");
}
System.out.println(" ");
int c;
ByteArrayInputStream bInput = new ByteArrayInputStream(b);
System.out.println("Converting characters to Upper case " );
for(int y = 0 ; y < 1; y++ ) {
while(( c= bInput.read())!= -1) {
System.out.println(Character.toUpperCase((char)c));
}
bInput.reset();
}
}
}

Here is the sample run of the above program:

asdfghjkly
Print the content
a s d f g h j k l y
Converting characters to Upper case
A
S
D
F
G
H
J
K
L
Y

DataInputStream

The DataInputStream is used in the context of DataOutputStream and can be used to read primitives.

Following is the constructor to create an InputStream:

InputStream in = DataInputStream(InputStream in);

Once you have DataInputStream object in hand, then there is a list of helper methods, which can be used to read the stream or to do other operations on the stream.
SNMethods with Description
1public final int read(byte[] r, int off, int len)throws IOException
Reads up to len bytes of data from the input stream into an array of bytes. Returns the total number of bytes read into the buffer otherwise -1 if it is end of file.
2Public final int read(byte [] b)throws IOException
Reads some bytes from the inputstream an stores in to the byte array. Returns the total number of bytes read into the buffer otherwise -1 if it is end of file.
3(a) public final Boolean readBooolean()throws IOException,
(b) public final byte readByte()throws IOException,
(c) public final short readShort()throws IOException
(d) public final Int readInt()throws IOException

These methods will read the bytes from the contained InputStream. Returns the next two bytes of the InputStream as the specific primitive type.
4public String readLine() throws IOException
Reads the next line of text from the input stream. It reads successive bytes, converting each byte separately into a character, until it encounters a line terminator or end of file; the characters read are then returned as a String.
Example:

Following is the example to demonstrate DataInputStream and DataInputStream. This example reads 5 lines given in a file test.txt and convert those lines into capital letters and finally copies them into another file test1.txt.

import java.io.*;
public class Test{
public static void main(String args[])throws IOException{
DataInputStream d = new DataInputStream(new
FileInputStream("test.txt"));
DataOutputStream out = new DataOutputStream(new
FileOutputStream("test1.txt"));
String count;
while((count = d.readLine()) != null){
String u = count.toUpperCase();
System.out.println(u); out.writeBytes(u + " ,");
}
d.close();
out.close();
}
}

Here is the sample run of the above program:

THIS IS TEST 1 ,
THIS IS TEST 2 ,
THIS IS TEST 3 ,
THIS IS TEST 4 ,
THIS IS TEST 5 ,
FileOutputStream:

FileOutputStream is used to create a file and write data into it. The stream would create a file, if it doesn't already exist, before opening it for output.
Here are two constructors which can be used to create a FileOutputStream object.
Following constructor takes a file name as a string to create an input stream object to write the file:

OutputStream f = new FileOutputStream("C:/java/hello")

Following constructor takes a file object to create an output stream object to write the file. First, we create a file object using File() method as follows:

File f = new File("C:/java/hello");
OutputStream f = new FileOutputStream(f);

Once you have OutputStream object in hand, then there is a list of helper methods, which can be used to write to stream or to do other operations on the stream.
SNMethods with Description
1public void close() throws IOException{}
This method closes the file output stream. Releases any system resources associated with the file. Throws an IOException.
2protected void finalize()throws IOException {}
This method cleans up the connection to the file. Ensures that the close method of this file output stream is called when there are no more references to this stream. Throws an IOException.
3public void write(int w)throws IOException{}
This methods writes the specified byte to the output stream.
4public void write(byte[] w)
Writes w.length bytes from the mentioned byte array to the OutputStream.
There are other important output streams available, for more detail you can refer to the following links:
  • ByteArrayOutputStream
  • DataOutputStream
ByteArrayOutputStream

The ByteArrayOutputStream class stream creates a buffer in memory and all the data sent to the stream is stored in the buffer. There are following forms of constructors to create ByteArrayOutputStream objects

Following constructor creates a buffer of 32 byte:

OutputStream bOut = new ByteArrayOutputStream()

Following constructor creates a buffer of size int a:

OutputStream bOut = new ByteArrayOutputStream(int a)

Once you have ByteArrayOutputStream object in hand then there is a list of helper methods which can be used to write the stream or to do other operations on the stream.
SNMethods with Description
1public void reset()
This method resets the number of valid bytes of the byte array output stream to zero, so all the accumulated output in the stream will be discarded.
2public byte[] toByteArray()
This method creates a newly allocated Byte array. Its size would be the current size of the output stream and the contents of the buffer will be copied into it. Returns the current contents of the output stream as a byte array.
3public String toString()
Converts the buffer content into a string. Translation will be done according to the default character encoding. Returns the String translated from the buffer's content.
4public void write(int w)
Writes the specified array to the output stream.
5public void write(byte []b, int of, int len)
Writes len number of bytes starting from offset off to the stream.
6public void writeTo(OutputStream outSt)
Writes the entire content of this Stream to the specified stream argument.
Example:

Following is the example to demonstrate ByteArrayOutputStream and ByteArrayOutputStream

import java.io.*;
public class ByteStreamTest {
public static void main(String args[])throws IOException {
ByteArrayOutputStream bOutput = new ByteArrayOutputStream(12);
while( bOutput.size()!= 10 ) {
// Gets the inputs from the user
bOutput.write(System.in.read());
}
byte b [] = bOutput.toByteArray();
System.out.println("Print the content");
for(int x= 0 ; x < b.length; x++) {
//printing the characters
System.out.print((char)b[x] + " ");
}
System.out.println(" ");
int c;
ByteArrayOutputStream bInput = new ByteArrayOutputStream(b);
System.out.println("Converting characters to Upper case " );
for(int y = 0 ; y < 1; y++ ) {
while(( c= bInput.read())!= -1) {
System.out.println(Character.toUpperCase((char)c));
}
bInput.reset();
}
}
}

Here is the sample run of the above program:

asdfghjkly
Print the content
a s d f g h j k l y
Converting characters to Upper case
A
S
D
F
G
H
J
K
L
Y

DataOutputStream

The DataOutputStream stream let you write the primitives to an output source.

Following is the constructor to create a DataOutputStream.

DataOutputStream out = DataOutputStream(OutputStream out);

Once you have DataOutputStream object in hand, then there is a list of helper methods, which can be used to write the stream or to do other operations on the stream.
SNMethods with Description
1public final void write(byte[] w, int off, int len)throws IOException
Writes len bytes from the specified byte array starting at point off , to the underlying stream.
2Public final int write(byte [] b)throws IOException
Writes the current number of bytes written to this data output stream. Returns the total number of bytes write into the buffer.
3(a) public final void writeBooolean()throws IOException,
(b) public final void writeByte()throws IOException,
(c) public final void writeShort()throws IOException
(d) public final void writeInt()throws IOException

These methods will write the specific primitive type data into the output stream as bytes.
4Public void flush()throws IOException
Flushes the data output stream.
5public final void writeBytes(String s) throws IOException
Writes out the string to the underlying output stream as a sequence of bytes. Each character in the string is written out, in sequence, by discarding its high eight bits.
Example:

Following is the example to demonstrate DataInputStream and DataOutputStream. This example reads 5 lines given in a file test.txt and converts those lines into capital letters and finally copies them into another file test1.txt.

import java.io.*;
public class Test{
public static void main(String args[])throws IOException{
DataInputStream d = new DataInputStream(new
FileInputStream("test.txt"));
DataOutputStream out = new DataOutputStream(
new FileOutputStream("test1.txt"));
String count;
while((count = d.readLine()) != null){
String u = count.toUpperCase();
System.out.println(u);
out.writeBytes(u + " ,");
}
d.close();
out.close();
}
}

Here is the sample run of the above program:

THIS IS TEST 1 ,
THIS IS TEST 2 ,
THIS IS TEST 3 ,
THIS IS TEST 4 ,
THIS IS TEST 5 ,

Example:

Following is the example to demonstrate InputStream and OutputStream:

import java.io.*;
public class fileStreamTest{
public static void main(String args[]){
try{
byte bWrite [] = {11,21,3,40,5};
OutputStream os = new FileOutputStream("test.txt");
for(int x=0; x < bWrite.length ; x++){
os.write( bWrite[x] ); // writes the bytes
}
os.close();
InputStream is = new FileInputStream("test.txt");
int size = is.available();
for(int i=0; i< size; i++){
System.out.print((char)is.read() + " ");
}
is.close();
}catch(IOException e){
System.out.print("Exception");
}
}
}

The above code would create file test.txt and would write given numbers in binary format. Same would be output on the stdout screen.

File Navigation and I/O:

There are several other classes that we would be going through to get to know the basics of File Navigation and I/O.
  • File Class
  • FileReader Class
  • FileWriter Class
File Class

Java File class represents the files and directory pathnames in an abstract manner. This class is used for creation of files and directories, file searching, file deletion etc.

The File object represents the actual file/directory on the disk. There are following constructors to create a File object:

Following syntax creates a new File instance from a parent abstract pathname and a child pathname string.

File(File parent, String child);

Following syntax creates a new File instance by converting the given pathname string into an abstract pathname.

File(String pathname)

Following syntax creates a new File instance from a parent pathname string and a child pathname string.

File(String parent, String child)

Following syntax creates a new File instance by converting the given file: URI into an abstract pathname.

File(URI uri)

Once you have File object in hand then there is a list of helper methods which can be used manipulate the files.
SNMethods with Description
1public String getName()
Returns the name of the file or directory denoted by this abstract pathname.
2public String getParent()
Returns the pathname string of this abstract pathname's parent, or null if this pathname does not name a parent directory.
3public File getParentFile()
Returns the abstract pathname of this abstract pathname's parent, or null if this pathname does not name a parent directory.
4public String getPath()
Converts this abstract pathname into a pathname string.
5public boolean isAbsolute()
Tests whether this abstract pathname is absolute. Returns true if this abstract pathname is absolute, false otherwise
6public String getAbsolutePath()
Returns the absolute pathname string of this abstract pathname.
7public boolean canRead()
Tests whether the application can read the file denoted by this abstract pathname. Returns true if and only if the file specified by this abstract pathname exists and can be read by the application; false otherwise.
8public boolean canWrite()
Tests whether the application can modify to the file denoted by this abstract pathname. Returns true if and only if the file system actually contains a file denoted by this abstract pathname and the application is allowed to write to the file; false otherwise.
9public boolean exists()
Tests whether the file or directory denoted by this abstract pathname exists. Returns true if and only if the file or directory denoted by this abstract pathname exists; false otherwise
10public boolean isDirectory()
Tests whether the file denoted by this abstract pathname is a directory. Returns true if and only if the file denoted by this abstract pathname exists and is a directory; false otherwise.
11public boolean isFile()
Tests whether the file denoted by this abstract pathname is a normal file. A file is normal if it is not a directory and, in addition, satisfies other system-dependent criteria. Any non-directory file created by a Java application is guaranteed to be a normal file. Returns true if and only if the file denoted by this abstract pathname exists and is a normal file; false otherwise.
12public long lastModified()
Returns the time that the file denoted by this abstract pathname was last modified. Returns a long value representing the time the file was last modified, measured in milliseconds since the epoch (00:00:00 GMT, January 1, 1970), or 0L if the file does not exist or if an I/O error occurs.
13public long length()
Returns the length of the file denoted by this abstract pathname. The return value is unspecified if this pathname denotes a directory.
14public boolean createNewFile() throws IOException
Atomically creates a new, empty file named by this abstract pathname if and only if a file with this name does not yet exist. Returns true if the named file does not exist and was successfully created; false if the named file already exists.
15public boolean delete()
Deletes the file or directory denoted by this abstract pathname. If this pathname denotes a directory, then the directory must be empty in order to be deleted. Returns true if and only if the file or directory is successfully deleted; false otherwise.
16public void deleteOnExit()
Requests that the file or directory denoted by this abstract pathname be deleted when the virtual machine terminates.
17public String[] list()
Returns an array of strings naming the files and directories in the directory denoted by this abstract pathname.
18public String[] list(FilenameFilter filter)
Returns an array of strings naming the files and directories in the directory denoted by this abstract pathname that satisfy the specified filter.
19public File[] listFiles()
Returns an array of abstract pathnames denoting the files in the directory denoted by this abstract pathname.
20public File[] listFiles(FileFilter filter)
Returns an array of abstract pathnames denoting the files and directories in the directory denoted by this abstract pathname that satisfy the specified filter.
21public boolean mkdir()
Creates the directory named by this abstract pathname. Returns true if and only if the directory was created; false otherwise.
22public boolean mkdirs()
Creates the directory named by this abstract pathname, including any necessary but nonexistent parent directories. Returns true if and only if the directory was created, along with all necessary parent directories; false otherwise.
23public boolean renameTo(File dest)
Renames the file denoted by this abstract pathname. Returns true if and only if the renaming succeeded; false otherwise.
24public boolean setLastModified(long time)
Sets the last-modified time of the file or directory named by this abstract pathname. Returns true if and only if the operation succeeded; false otherwise.
25public boolean setReadOnly()
Marks the file or directory named by this abstract pathname so that only read operations are allowed. Returns true if and only if the operation succeeded; false otherwise.
26public static File createTempFile(String prefix, String suffix, File directory) throws IOException
Creates a new empty file in the specified directory, using the given prefix and suffix strings to generate its name. Returns an abstract pathname denoting a newly-created empty file.
27public static File createTempFile(String prefix, String suffix) throws IOException
Creates an empty file in the default temporary-file directory, using the given prefix and suffix to generate its name. Invoking this method is equivalent to invoking createTempFile(prefix, suffix, null). Returns abstract pathname denoting a newly-created empty file.
28public int compareTo(File pathname)
Compares two abstract pathnames lexicographically. Returns zero if the argument is equal to this abstract pathname, a value less than zero if this abstract pathname is lexicographically less than the argument, or a value greater than zero if this abstract pathname is lexicographically greater than the argument.
29public int compareTo(Object o)
Compares this abstract pathname to another object. Returns zero if the argument is equal to this abstract pathname, a value less than zero if this abstract pathname is lexicographically less than the argument, or a value greater than zero if this abstract pathname is lexicographically greater than the argument.
30public boolean equals(Object obj)
Tests this abstract pathname for equality with the given object. Returns true if and only if the argument is not null and is an abstract pathname that denotes the same file or directory as this abstract pathname.
31public String toString()
Returns the pathname string of this abstract pathname. This is just the string returned by the getPath() method.
Example:

Following is the example to demonstrate File object:

package com.tutorialspoint;
import java.io.File;
public class FileDemo {
public static void main(String[] args) {
File f = null;
String[] strs = {"test1.txt", "test2.txt"};
try{
// for each string in string array
for(String s:strs )
{
// create new file
f= new File(s);
// true if the file is executable
boolean bool = f.canExecute();
// find the absolute path
String a = f.getAbsolutePath();
// prints absolute path
System.out.print(a);
// prints
System.out.println(" is executable: "+ bool);
}
}catch(Exception e){
// if any I/O error occurs
e.printStackTrace();
}
}
}

Consider there is an executable file test1.txt and another file test2.txt is non executable in current directory, Let us compile and run the above program, this will produce the following result:

test1.txt is executable: true test2.txt is executable: false

FileReader Class

This class inherits from the InputStreamReader class. FileReader is used for reading streams of characters.

This class has several constructors to create required objects.

Following syntax creates a new FileReader, given the File to read from.

FileReader(File file)

Following syntax creates a new FileReader, given the FileDescriptor to read from.

FileReader(FileDescriptor fd)

Following syntax creates a new FileReader, given the name of the file to read from.

FileReader(String fileName)

Once you have FileReader object in hand then there is a list of helper methods which can be used manipulate the files.
SNMethods with Description
1public int read() throws IOException
Reads a single character. Returns an int, which represents the character read.
2public int read(char [] c, int offset, int len)
Reads characters into an array. Returns the number of characters read.
Example:

Following is the example to demonstrate class:

import java.io.*;
public class FileRead{
public static void main(String args[])throws IOException{
File file = new File("Hello1.txt");
creates the file file.createNewFile();
creates a FileWriter Object
FileWriter writer = new FileWriter(file);
// Writes the content to the file
writer.write("This\n is\n an\n example\n");
writer.flush();
writer.close();
//Creates a FileReader Object
FileReader fr = new FileReader(file);
char [] a = new char[50];
fr.read(a); // reads the content to the array
for(char c : a)
System.out.print(c); //prints the characters one
by one fr.close();
}
}

This would produce the following result:

This
is
an
example

FileWriter Class

This class inherits from the OutputStreamWriter class. The class is used for writing streams of characters.

This class has several constructors to create required objects.

Following syntax creates a FileWriter object given a File object.

FileWriter(File file)

Following syntax creates a FileWriter object given a File object.

FileWriter(File file, boolean append)

Following syntax creates a FileWriter object associated with a file descriptor.

FileWriter(FileDescriptor fd)

Following syntax creates a FileWriter object given a file name.

FileWriter(String fileName)

Following syntax creates a FileWriter object given a file name with a boolean indicating whether or not to append the data written.

FileWriter(String fileName, boolean append)

Once you have FileWriter object in hand, then there is a list of helper methods, which can be used manipulate the files.
SNMethods with Description
1public void write(int c) throws IOException
Writes a single character.
2public void write(char [] c, int offset, int len)
Writes a portion of an array of characters starting from offset and with a length of len.
3public void write(String s, int offset, int len)
Write a portion of a String starting from offset and with a length of len.
Example:

Following is the example to demonstrate class:

import java.io.*;
public class FileRead{
public static void main(String args[])throws IOException{
File file = new File("Hello1.txt");
creates the file
file.createNewFile();
creates a FileWriter Object
FileWriter writer = new FileWriter(file);
// Writes the content to the file
writer.write("This\n is\n an\n example\n");
writer.flush();
writer.close();
//Creates a FileReader Object
FileReader fr = new FileReader(file);
char [] a = new char[50];
fr.read(a); // reads the content to the array
for(char c : a)
System.out.print(c); //prints the characters one
by one fr.close();
}
}

This would produce the following result:

This
is
an
example

Directories in Java:

A directory is a File which can contains a list of other files and directories. You use File object to create directories, to list down files available in a directory. For complete detail check a list of all the methods which you can call on File object and what are related to directories.

Creating Directories:

There are two useful File utility methods, which can be used to create directories:
  • The mkdir( ) method creates a directory, returning true on success and false on failure. Failure indicates that the path specified in the File object already exists, or that the directory cannot be created because the entire path does not exist yet.
  • The mkdirs() method creates both a directory and all the parents of the directory.
Following example creates "/tmp/user/java/bin" directory:

import java.io.File;
public class CreateDir {
public static void main(String args[]) {
String dirname = "/tmp/user/java/bin";
File d = new File(dirname);
// Create directory now. d.mkdirs();
}
}

Compile and execute above code to create "/tmp/user/java/bin".

Note: Java automatically takes care of path separators on UNIX and Windows as per conventions. If you use a forward slash (/) on a Windows version of Java, the path will still resolve correctly.

Listing Directories:

You can use list( ) method provided by File object to list down all the files and directories available in a directory as follows:

import java.io.File;
public class ReadDir {
public static void main(String[] args) {
File file = null;
String[] paths;
try{
// create new file object
file = new File("/tmp");
// array of files and directory
paths = file.list();
// for each name in the path array
for(String path:paths)
{ // prints filename and directory name
System.out.println(path);
}
}catch(Exception e){
// if any error occurs
e.printStackTrace();
}
}
}

This would produce following result based on the directories and files available in your /tmp directory:

test1.txt
test2.txt
ReadDir.java
ReadDir.class
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