JAVA TUTORIALS FOR BEGINNER: tutoria

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Java
 exception handling tutorial: In this tutorial we will learn how to 
handle exception with the help of suitable examples. Exceptions are 
errors which occur when the program is executing. Consider the Java 
program below which divides two integers. 
<div class="geshifilter">
<pre class="java geshifilter-java" style="font-family: monospace;"> </pre>
<pre class="java geshifilter-java" style="font-family: monospace;">import java.util.Scanner;
 
class Division {
 public static void main(String[] args) {
 
 int a, b, result;
 
 Scanner input = new Scanner(System.in);
 System.out.println("Input two integers");
 
 a = input.nextInt();
 b = input.nextInt();
 
 result = a / b;
 
 System.out.println("Result = " + result);
 }
}</pre>
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Now we compile and execute the above code two times, see the output of program in two cases: 
 
<img alt="Java program throwing Arithmetic exception (division by zero)." src="http://www.programmingsimplified.com/images/java/division-by-zero-exception-java-program.png" /> 
 
In the second case we are dividing a by zero which is not allowed in 
mathematics, so a run time error will occur i.e. an exception will 
occur. If we write programs in this way then they will be terminated 
abnormally and user who is executing our program or application will not
 be happy. This occurs because input of user is not valid so we have to 
take a preventive action and the best thing will be to notify the user 
that it is not allowed or any other meaningful message which is relevant
 according to context. You can see the information displayed when 
exception occurs it includes name of thread, file name, line of code (14
 in this case) at which exception occurred, name of exception 
(ArithmeticException) and it's description('/ by zero'). Note that 
exceptions don't occur only because of invalid input only there are 
other reasons which are beyond of programmer control such as stack 
overflow exception, out of memory exception when an application requires
 memory larger than what is available. 
Java provides a powerful way to handle such exceptions which is known
 as exception handling. In it we write vulnerable code i.e. code which 
can throw exception in a separate block called as <code class="java geshifilter-java">try</code> block and exception handling code in another block called <code class="java geshifilter-java">catch</code> block. Following modified code handles the exception. 
<h2>
Java exception handling example</h2>
<div class="geshifilter">
<pre class="java geshifilter-java" style="font-family: monospace;">class Division {
 public static void main(String[] args) {
 
 int a, b, result;
 
 Scanner input = new Scanner(System.in);
 System.out.println("Input two integers");
 
 a = input.nextInt();
 b = input.nextInt();
 
 // try block
 
 try {
 result = a / b;
 System.out.println("Result = " + result);
 }
 
 // catch block
 
 catch (ArithmeticException e) {
 System.out.println("Exception caught: Division by zero.");
 }
 }
}</pre>
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Whenever an exception is caught corresponding catch block is 
executed, For example above code catches ArithmeticException only. If 
some other kind of exception is thrown it will not be caught so it's the
 programmer work to take care of all exceptions as in our try block we 
are performing arithmetic so we are capturing only arithmetic 
exceptions. A simple way to capture any exception is to use an object of
 Exception class as other classes inherit Exception class, see another 
example below: 
<div class="geshifilter">
<pre class="java geshifilter-java" style="font-family: monospace;">class Exceptions {
 public static void main(String[] args) {
 
 String languages[] = { "C", "C++", "Java", "Perl", "Python" };
 
 try {
 for (int c = 1; c <= 5; c++) {
 System.out.println(languages[c]);
 }
 }
 catch (Exception e) {
 System.out.println(e);
 }
 }
}</pre>
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Output 
<div class="geshifilter">
<pre class="java geshifilter-java" style="font-family: monospace;"> </pre>
<pre class="java geshifilter-java" style="font-family: monospace;">C++
Java
Perl
Python
java.lang.ArrayIndexOutOfBoundsException: 5</pre>
</div>
Here our catch block capture an exception which occurs because we are
 trying to access an array element which does not exists (languages[5] 
in this case). Once an exception is thrown control comes out of try 
block and remaining instructions of try block will not be executed. At 
compilation time syntax and semantics checking is done and code is not 
executed on machine so exceptions can only be detected at run time. 
<h2>
Finally block in Java</h2>
Finally block is always executed whether an exception is thrown or not. 
<div class="geshifilter">
<pre class="java geshifilter-java" style="font-family: monospace;">class Allocate {
 public static void main(String[] args) {
 
 try {
 long data[] = new long[1000000000]; 
 }
 catch (Exception e) {
 System.out.println(e);
 }
 
 finally {
 System.out.println("finally block will execute always.");
 }
 }
}</pre>
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Output 
 
<div class="geshifilter">
<pre class="java geshifilter-java" style="font-family: monospace;">finally block will execute always.
Exception in thread "main" java.lang.OutOfMemoryError: Java heap space
at Allocate.main(Allocate.java:5)</pre>
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Exception occurred because we try to allocate a large amount of 
memory which is not available. This amount of memory may be available on
 your system if this is the case try increasing the amount of memory to 
allocate through the program.</div>
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Java exception handling tutorial with example programs

Java exception handling tutorial: In this tutorial we will learn how to handle exception with the help of suitable examples. Excep...

JAVA TUTORIALS FOR BEGINNER

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Java exception handling tutorial with example programs