Basic i/o & file handling in java

EXCEPTION HANDLING AND
BASIC I/O AND
FILE HANDLING

TOPICS WE DISCUS
❏ EXCEPTION HANDLING
❏ GENERAL PRINCIPLES OF I/O
❏ JAVA FILE CLASS
❏ JAVA I/O API
❏ JAVA SCANNER CLASS
❏ JAVA SERIALIZATION
2

What is an Exception?
An exception is an unexpected event that occurs during program
execution. It affects the flow of the program instructions which can
cause the program to terminate abnormally.
An exception can occur for many reasons. Some of them are:
● Invalid user input
● Device failure
● Loss of network connection
● Physical limitations (out of disk memory)
● Code errors
● Opening an unavailable file
4

Java Exception hierarchy
5
Exception, that means exceptional errors. Actually exceptions are
used for handling errors.Error that occurs during runtime .Cause
normal program flow to be disrupted
There is two type of Exception
Classifications
Unchecked- Occur in Run-time
Checked- Occur in Compile-time

Common Exceptions
Unchecked Exception
ArithmeticException--thrown if a program attempts to perform
division by zero
ArrayIndexOutOfBoundsException--thrown if a program
attempts to access an index of an array that does not exist
StringIndexOutOfBoundsException--thrown if a program
attempts to access a character at a non-existent index in a
String
NullPointerException--thrown if the JVM attempts to perform an
operation on an Object that points to no data, or null
6

Common Exceptions
NumberFormatException--thrown if a program is attempting to
convert a string to a numerical data type, and the string
contains inappropriate characters (i.e. 'z' or 'Q')
Checked Exceptions
ClassNotFoundException--thrown if a program can not find a
class it depends at runtime (i.e., the class's ".class" file cannot
be found or was removed from the CLASSPATH)
FileNotFoundException--when a file with the specified
pathname does not exist.
IOException--actually contained in java.io, but it is thrown if
the JVM failed to open an I/O stream
7

Exception Handling
In Java, we use the exception handler components try, catch and
finally blocks to handle exceptions.
To catch and handle an exception, we place the try...catch...finally
block around the code that might generate an exception. The finally
block is optional.
we can now catch more than one type of exception in a single catch
block.Each exception type that can be handled by the catch block is
separated using a vertical bar or pipe |.
catch (ExceptionType1 e1|ExceptionType2 e2) {
// catch block
}
8

Try Catch Finally
Try..catch block
try {
// code
} catch (ExceptionType e) {
// catch block
}
9
Try..catch..finally block
try {
// code
} catch (ExceptionType e) {
// catch block
} finally {
// finally block
}

throw, throws statement
Throw
The throw keyword is used to throw an exception explicitly. Only
object of Throwable class or its sub classes can be thrown. Program
execution stops on encountering throw statement, and the closest catch
statement is checked for matching type of exception
Throws
The throws keyword is used to declare the list of exception that a
method may throw during execution of program. Any method that is
capable of causing exceptions must list all the exceptions possible during
its execution, so that anyone calling that method gets a prior knowledge
about which exceptions are to be handled.
10

Error and Exception
An error is an irrecoverable condition occurring at runtime.
Though error can be caught in catch block but the execution of
application will come to a halt and is not recoverable.
While exceptions are conditions that occur because of bad input
etc.
In most of the cases it is possible to recover from an exception.
11

2.
General Principles Of I/O
12

Streams
All modern I/O is stream-based
A stream is a connection to a source of data or to a destination for
data (sometimes both)
An input stream may be associated with the keyboard
An input stream or an output stream may be associated with a file
Different streams have different characteristics:
A file has a definite length, and therefore an end
Keyboard input has no specific end
13

14
How TO Do
import java.io.*;
*Open the stream
*Use the stream
(read, write, or both)
*Close the stream
.

There is data external to your program that you want to get, or you
want to put data somewhere outside your program
When you open a stream, you are making a connection to that
external place
Once the connection is made, you forget about the external place
and just use the stream
Opening a Stream
15

Opening a Stream: Example
A FileReader is used to connect to a file that will be used for input:
FileReader fileReader = new FileReader (fileName);
The fileName specifies where the (external) file is to be found
You never use fileName again; instead, you use fileReader
16

Using a Stream
Some streams can be used only for input, others only for output,
still others for both
Using a stream means doing input from it or output to it
But it’s not usually that simple you need to manipulate the data in
some way as it comes in or goes out
17

Using a Stream :Example
int ch;
ch = FileReader.read( );
The FileReader.read() method reads one character and returns it
as an integer, or -1 if there are no more characters to read
The meaning of the integer depends on the file encoding (ASCII,
Unicode, other)
18

Using BufferReader
A BufferedReader will convert integers to characters; it can also
read whole lines
The constructor for BufferedReader takes a FileReader
parameter:
BufferedReader bufferedReader =
new BufferedReader(fileReader);
19

Closing
20
A stream is an expensive resource
There is a limit on the number of streams that you can have open at
one time
You should not have more than one stream open on the same file
You must close a stream before you can open it again
Always close your streams!

File class
The File class in the Java IO API gives you access to the
underlying file system.
The File class is Java's representation of a file or directory path
name.
This class offers a rich set of static methods for reading, writing,
and manipulating files and directories.
The Files methods work on instances of Path objects
22

Operations in File class
The File class contains several methods for working with the path
name:
Check if a file exists.
Read the length of a file.
Rename or move a file/ Directory.
Delete a file/ Directory.
Check if path is file or directory.
Read list of files in a directory.
23

Creating a File object
You create a File object by passing in a String that represents the
name of a file.
For example,
File a = new File("/usr/local/bin/smurf");
This defines an abstract file name for the smurf file in
directory /usr/local/bin.
This is an absolute abstract file name.
You could also create a file object as follows:
File b = new File("bin/smurf");
This is a relative abstract file name
24

File Object Methods
Boolean exists() : Returns true if
the file exist.
Boolean canRead() : Returns true if
the file is readable.
Boolean canWrite() : Returns true
if the file is writable.
Boolean isAbsolute() : Returns true
if the file name is an absolute path
name.
25
Boolean isDirectory() : Returns
true if the file name is a directory.
Boolean isFile() : Returns true if
the file name is a "normal" file
(depends on OS)
Boolean isHidden() : Returns true
if the file is marked "hidden“.
long lastModified() : Returns a long
indicating the last time the file was
modified.

File Object Methods
long length() : Returns the length
of the contents of the file.
Boolean setReadOnly() : Marks
the file read-only (returns true if
succeeded)
void setLastModified(long) :
Explicitly sets the modification
time of a file
Boolean createNewFile() :
Creates a new file with this
abstract file name.
26
Returns true if the file was
created, false if the file already
existed.
Boolean delete(): Deletes the
file specified by this file name.
Boolean mkdir() : Creates this
directory.All parent directories
must already exist.
Boolean mkdirs() : Creates this
directory and any parent
directories that do not exist.

Reader class
The Reader class is the base class for all Reader's in the Java IO
API.
A Reader is like an InputStream except that it is character based
rather than byte based.
28

FileReader Class
Java FileReader class is used to read data from file .it return in
bytes format like FileInputstream.It is character-oriented class
which is used for file handling in java.
Object creation:
FileReader fr=new FileReader("path");
29

BufferedReader Class
Java BufferedReader class is used to read the text from a
character-based input stream. It can be used to read data line by
line by readLine() method. It makes the performance fast. It
inherits Reader class.
Object creation:
BufferedReader br= new BufferedReader();
30

Writer class
The Writer class is the base class for all Writer's in the Java IO
API.
A Writer is like an OutputStream except that it is character based
rather than byte based.
You will normally use a Writer subclass rather than a Writer
31

FileWritter Class
Java FileWriter class is used to write character-oriented data to a
file. It is character-oriented class which is used for file handling in
java.Unlike FileOutputStream class, you don't need to convert
string into byte array because it provides method to write string
directly.
Object creation:
FileWriter fw=new FileWriter("path");
32

BufferedWitter Class
Java BufferedWriter class is used to provide buffering for Writer
instances. It makes the performance fast. It inherits Writer class.
The buffering characters are used for providing the efficient
writing of single arrays, characters, and strings.
Object creation:
BufferedWritter bw= new BufferedWritter();
33

Scanner Class
Scanner class in Java is found in the java.util package. Java
provides various ways to read input from the keyboard, the
java.util.Scanner class is one of them.
The Java Scanner class is widely used to parse text for strings and
primitive types using a regular expression. It is the simplest way to
get input in Java. By the help of Scanner in Java, we can get input
from the user in primitive types such as int, long, double, byte,
float, short, etc.
35

Scanner Methods
For each of the primitive types there is a corresponding nextXxx()
method that returns a value of that type. If the string cannot be
interpreted as that type, then an InputMismatchException is
thrown.
int nextInt() : Returns the next token as an int.
long nextLong() : Returns the next token as a long.
float nextFloat() : Returns the next token as a float.
double nextDouble() : Returns the next token as a long.
36

Scanner Methods
String nextLine() : Returns the rest of the current line, excluding
any line separator at the end.
String next() : Finds and returns the next complete token from this
scanner and returns it as a string; a token is usually ended by
whitespace such as a blank or line break. If not token exists,
NoSuchElementException is thrown.
void close() : Closes the scanner.
37

Using a Scanner Class
To use the Scanner utility, we need to create an object.
Scanner Scan = new Scanner();
To get user input the above we need to use the system input
stream.
Scanner Scan = new Scanner( System.in );
The user input will be printed to the screen using the below
syntax.
System.out.println( Scan.nextLine() );
This will receive the input of the next line of text someone
types into the keyboard.
38

Object Serialization
Serialization in Java is a mechanism of writing the state of an
object into a byte-stream.
The reverse operation of serialization is called deserialization
where byte-stream is converted into an object. The serialization
and deserialization process is platform-independent, it means you
can serialize an object in a platform and deserialize in different
platform.
40

Using a Scanner Class
41
Serialization
Deserialization
Object Byte
Stream

Basic i/o & file handling in java

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