..
JAVA PROGRAMMING NOTES
PART 4
,..
Module 4
Java - 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.
Stream
A stream can be defined as a sequence of data. There are two kinds of Streams − InPutStream
− The InputStream is used to read data from a
source.
OutPutStream − The OutputStream is used for writing data to a destination.
Streams
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 will see the most commonly used
examples 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 and
FileOutputStream. Following is an example which makes use of these two classes to copy an
input file into an output file −
Example 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 the 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 the 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, whereas Java Character
streams 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 the major difference is that FileReader reads two bytes at a time and FileWriter writes two
bytes at a time.
We can re-write the above example, which makes the use of these two classes to copy an input
file
(having unicode characters) into an output file −
Example 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 the 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 the above code in CopyFile.java
file and do the following −
JAVA PROGRAMMING NOTES
PART 4
,..
Module 4
Java - 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.
Stream
A stream can be defined as a sequence of data. There are two kinds of Streams − InPutStream
− The InputStream is used to read data from a
source.
OutPutStream − The OutputStream is used for writing data to a destination.
Streams
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 will see the most commonly used
examples 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 and
FileOutputStream. Following is an example which makes use of these two classes to copy an
input file into an output file −
Example 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 the 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 the 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, whereas Java Character
streams 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 the major difference is that FileReader reads two bytes at a time and FileWriter writes two
bytes at a time.
We can re-write the above example, which makes the use of these two classes to copy an input
file
(having unicode characters) into an output file −
Example 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 the 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 the above code in CopyFile.java
file and do the following −
