Exception Handling
Exceptions:
Exception,
that means exceptional errors. Actually exceptions are used for handling
errors in programs that occurs during the program execution. During the program
execution if any error occurs and you want to print your own message or the
system message about the error then you write the part of the program which
generate the error in the try{} block
and catch the errors using catch() block.
Exception turns the direction of normal flow of the program control and send to
the related catch() block.
Error that occurs during the program execution generate a specific object which
has the information about the errors occurred in the program.
In the following example code you will see that how the
exception handling can be done in java program. This example reads two integer
numbers for the variables a and b. If you enter any other character except
number ( 0 - 9 ) then the error is caught by NumberFormatException
object. After that ex.getMessage()
prints the information about the error occurring causes.
Code of the program :
import java.io.*;
public class exceptionHandle{
public static void main(String[] args) throws Exception{
try{
int a, b;
BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
a = Integer.parseInt(in.readLine());
b = Integer.parseInt(in.readLine());
}
catch (NumberFormatException ex){
System.out.println(ex.getMessage() + " is not a numeric value.");
System.exit(0);
}
}
}
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Output of this program:
C:\vinod\xml>javac exceptionHandle.java
C:\vinod\xml>java exceptionHandle
For input string: "" is not a numeric value. |
An exception is an event that occurs and interrupts the normal flow of instructions.
That is exceptions are objects that store the information about the occurrence
of errors. When any kind of error or unusual condition occurs, these exceptions
are being thrown. Any exception used to occur earlier always resulted in a
program crash. However, some programming languages like java have mechanisms for
handling exceptions. This is known as catching exception in Java. The exceptions that occur in the program can be caught using try and catch
block. Remember, the program will crash if the exception would not be
caught. There are three types of exceptions in Java. These are -:
1. Checked Exceptions
2. The error
3. Runtime exception
Error and Runtime exceptions are known as unchecked exceptions. This chapter
covers how to throw an exception and catch it. A detailed explanation on the
types of exceptions and the advantages of the exceptions.
Basic I/O:
In this section we will learn about basic input and out put operations in
Java. Different kinds of sources and destinations are represented by a Stream
like disk files, devices, memory arrays etc. A Stream is a sequence
of data. An Input Stream is used by the program to read data from the
source. Similarly, a program uses an Output stream to write data to a
destination. It also supports different kinds of data including simple bytes,
primitive data types, objects etc. We will learn about I/O Steams and how to use
them.
Concurrency:
Concurrency is generally used to perform multiple tasks simultaneously. In this
section we will learn how to write applications to perform multitasking. There
are two types of units of execution process and threads. Thread is the most
important unit in concurrent programming. There are many processes and threads
which are active in a computer system. However only one threads executes at a
time even in systems that only have a single execution core.
Regular expression
The set of strings which are based on common characteristics are shared by each
string in the set. Basically, Regular expressions are are a set of strings.
This regular expression as a Java string, becomes "\\\\".
That is 4 backslashes to match a single one. As in literal Java strings the
backslash is an escape character. The literal string as a single backslash is
denoted by "\\". In
this chapter we will learn to create a syntax for regular expressions and how to
use them.
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Current Comments
3 comments so far (post your own) View All Comments Latest 10 Comments:this site really a gift!!!!
Posted by sparsh on Saturday, 05.10.08 @ 12:30pm | #59083
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Posted by Dinesh Kumar on Tuesday, 04.1.08 @ 15:51pm | #55038
Hi..
Very nice nice topic.
Its really very helpful.
Thanks
harikesh
Posted by Harikesh on Thursday, 10.11.07 @ 18:01pm | #33069