Java Exceptions Tutorial

Exceptions in Java - Notes

 

  Table of Contents

Types of Exceptions
A program without Exception
A program with try-catch
One try and multiple catch blocks
Nested try-catch
Use of printStackTraceMethod 
User Defined Exceptions 

Practice Quesstions on Java Exceptions

 

Introduction

Basically, errors are two types in programming development.

  1. Syntactical errors (Grammatical errors) occurs at compile time. 
  2. Semantic errors (Logical errors) occurs at runtime.   

 

What is an Exception?

Exception is nothing but a runtime error. Handling exception is called Exception Handling
Exception is a some abnormal condition that occur during the execution of the program.
Exception handler traps the runtime errors and makes the program execute smoothly and completely without any interruption.

 
 

 Exception superclass is ------ Throwable. It is available in java.lang package. 

 

Throwable again subdivided into 2 classes

1. Error Class  – These are hardware related errors. Also called as unchecked Exception can't be handled by code. Ex. Memory corrupted, Data corrupted, file not found, connection not established…etc. thrown by JVM.

2. Exception Class – It is checked exception can be handled. Thrown by java API, i.e., thrown by code.

 

 

 

Menu

Types of Exceptions in Java

  • ArithmaticException - Occurs when a number is divided by zero Ex: result = 4/0;   
  • NumberFormatException - Occurs if you enter a Char in place of Number  
  • NullPointerException - when trying to read value from null variable   
  • ArrayIndexOutofBoundsException -  where there are no sufficient elements in an array
  • ClassNotFoundException - when you are trying to access a class that is not available  
  • IllegalAccessException  - when there is no access permission to a file. 
  • InterruptedException - when a running application is interrupted, it usually occurs in threads.
  • NoSuchMethodException - when you're trying to access the method that is not available  
  •  IlligalArgumentException - when the passed argument is not matched.


 

Move to Menu

To handle Exceptions there are 5 keywords are available in Java.

        1. try  
        2. catch  
        3. finally 
        4. throw 
        5. throws

Error possibility code is enclosed in try..catch block. 

 

Exception Handling in Java.

 

syn:
 
try{
	.....
	.....
}catch(<Exception> e)
{
	sop(e);
}
.....
 
 
 

 
 
 
 
 

A program without Exception 

ex1:
public class Expdemo{
	public static void main(String args[]){
		int d=0;
		int a=24/d;
		System.out.println(a);
	}
}
 
Result:
C:\Exceptions>java Expdemo
Exception in thread "main" java.lang.ArithmeticException: / by zero
        at Exp.main(Exp.java:4) 
 
ex2:

Move to Menu

A program using try..catch

Using  try...catch, Handling runtime errors

 
 
 
public class Expdemo1{
	public static void main(String args[]){
		int num;
		int d=0;
		try{
			num = 24/d;
			System.out.println("This is not printer");
		}
		catch(ArithmeticException ae)
		{
			System.out.println("Divide by Zero");
		}
		System.out.println("After the try...catch");
	}
}
 
Result
C:\Exceptions>java java Expdemo1
Divide by Zero
After the try...catch 

Menu  

finally

-- finally block follows the catch block finally block contains the code for releasing resource at the end of the program. Ex. closing an opened file or closing a database connection etc.

 -- whether an exception raised or not finally must be executed. 

syn:
 
try{
	....
	....
}
catch(Exp1 e1)
{ sop(e1);}
finally
{
	cleanup;
}
 
 
ex:
---
public class Finallydemo{
	public static void main(String args[]){
		int num;
		int d=0;
		try{
			num = 24/d;
			System.out.println("This is not printer");
		}
		catch(ArithmeticException ae)
		{
			System.out.println("Divide by Zero");
		}
		finally
		{
			System.out.println("End of the program");
		}
	}
}
 
Result:
C:\Exceptions>java Finallydemo
Divide by Zero
End of the program 
 
 

One try and multiple catch blocks 

try{
	....
	....
}
catch(Exp1 e1)
{ sop(e1);}
catch(Exp2 e2)
{ sop(e1);}
 
public class Multicatchdemo
{
	public static void main(String args[]){
		int x;
		int y;
		int z;
		try{
			x=15;
			y=Integer.parseInt(args[0]);
			z=x/y;
			System.out.println("z="+z);
 
		catch(NumberFormatException ne)
		{
			System.out.println("Not a Number!!");
		}
		catch(ArithmeticException ae)
		{
			System.out.println("Divide by Zero");
		}
		catch(ArrayIndexOutOfBoundsException ae)
		{
			System.out.println("Missing Argument..!!");
		}
	}
}
 
Result:

C:\Exceptions>java Multicatchdemo
java.lang.ArrayIndexOutOfBoundsException: 0Missing Argument..!!


C:\Exceptions>java Multicatchdemo  j
java.lang.NumberFormatException: For input string: "j"


C:\Exceptions>java Multicatchdemo  2
z=7 

 

Go Top

 

In multi catch we should maintain the hierarchy means subclass exceptions should come first, and its super class is next to that.

In the following programs first Exception is declared next all child class exceptions are declared like Numberformat, Arithmetic, ArrayIndex..etc… These all errors handled by Exception. So JVM ignores and gives unreacted exceptions' error.

So first subclass exceptions and if any other exceptions raise which is not matched with subclass, then exception take care of them. Because it is the super class of all exceptions.

 
ex:
public class Multicatchdemo
{
	public static void main(String args[]){
		int x;
		int y;
		int z;
		try{
			x=15;
			y=Integer.parseInt(args[0]);
			z=x/y;
			System.out.println("z="+z);
		}
		catch(Exception e)
		{
			System.out.println("Error in a program!!");
		}
		catch(NumberFormatException ne)
		{
			System.out.println("Not a Number!!");
		}
		catch(ArithmeticException ae)
		{
			System.out.println("Divide by Zero");
		}
		catch(ArrayIndexOutOfBoundsException ae)
		{ System.out.println("Missing Argument..!!");}
	}
}
 
 
 
Result: Compilation Error
C:\Exceptions>javac Multicatchdemo.java
Multicatch1.java:17: error: exception NumberFormatException has already been caught
                catch(NumberFormatException ne)
                ^
Multicatch1.java:21: error: exception ArithmeticException has already been caught
                catch(ArithmeticException ae)
                ^
Multicatch1.java:25: error: exception ArrayIndexOutOfBoundsException has already been caught
                catch(ArrayIndexOutOfBoundsException ae)
                ^
3 errors
 
 

The Exception catch block must have written as a last catch

The above code should be modified as shown below

 
ex:
public class Multicatchdemo
{
	public static void main(String args[]){
		int x;
		int y;
		int z;
		try{
			x=15;
			y=Integer.parseInt(args[0]);
			z=x/y;
			System.out.println("z="+z);
		}
		
		catch(NumberFormatException ne)
		{
			System.out.println("Not a Number!!");
		}
		catch(ArithmeticException ae)
		{
			System.out.println("Divide by Zero");
		}
		catch(ArrayIndexOutOfBoundsException ae)
		{ System.out.println("Missing Argument..!!");}
 
             catch(Exception e)
		{
			System.out.println("Error in a program!!");
		} }
}   
 
Result: No compilation error
output: 
C:\Exceptions>javac Multicatch1.java

C:\Exceptions>java Multicatch1
Missing Argument..!!

C:\Exceptions>java Multicatch1 j
Not a Number!!

C:\Exceptions>java Multicatch1 2
z=7

C:\Exceptions>
 

Menu Up


 
public class Aiobdemo{
	public static void main(String args[]){
		int a[]={10, 20, 30, 40, 50, 60 };
		try{
			for(int i=0;i<=a.length;i++)
			System.out.println(a[i]);
		}
		catch(ArrayIndexOutOfBoundsException ae)
		{ System.out.println("insufficient Array Size");}
	}
}
 
Result: 
C:\Exceptions>java Aiob
10
20
30
40
50
60
insufficient Array Size 
 

Menu Top

 

Nested try..catch

One try..catch, inside another try...catch block

(just like nested while, nested for..etc)

 

     try{
	| ....
	| ....
	|
	|----- ----try{
		| | ....
		| | ....
		| |
		| |
		| ----catch(Exp1 e1)
		| { sop(e1);}
		|
		|
	     | }
	----catch(Exp2 e2)
	{ sop(e1);}
 

Goto Menu

 
 
Ex:
public class Nestedcatch
{
	public static void main(String args[]){
		int a;
		int b;
		int c;
		a=15;
		try{
			b=Integer.parseInt(args[0]);
			try{
				c=a/b;
				System.out.println("c="+c);
			}
			catch(ArithmeticException ae)
			{
				System.out.println("Divide by Zero");
			}
		}
		catch(NumberFormatException e)
		{ System.out.println("Not a Number..!!");
		}
	}
}

throw

Throwing an exception to caller. So caller will handle that exception, i.e., that method should be called in try...catch block.

 

Menu

 

 Use of printStackTraceMethod()

This is method is declared in Throwable class. Traces the error where exactly it originated. by displaying the line no. 

public class ThrowDemo
{
	static void m1()
	{
		try{
			 throw new NullPointerException("Demo");
		}
		catch(NullPointerException ne)
		{
			System.out.println("Caught in m1()");
			throw ne;
		}
	}
	public static void main(String args[]){
		ThrowDemo td = ThrowDemo();
		try{
			tc.m1();
		}
		catch(NullPointerException ne){
			System.out.println("Re caught in main()");
		}
	}} 
 Result:
C:\Exceptions>java ThrowDemo
Caught in m1()
Re caught in main() 

 

 

Menu

 

throws

The method will declared as it throws an Exception. that should be catched by caller. 

Syn:
public void m1() throws NumberFormatException
{
	....
	....
}

while calling the methods should be enclosed in try...catch block and should be catched throwing exception 

if it is called in main...it should in try...catch()
try{
	m1();
	catch(NumberFormatException ne)
	{
		s.o.p(ne);
	}

Menu

 

User defined Exceptions in Java

***place both files in same file and save as MyExpTest.java 

public class MyException extends Exception {
	public MyException() {
	}
	public MyException(String msg) {
		super(msg);
	}
}
public class MyExpDemo {
	public static void arraySize(int size)throws MyException {
		if(size<0)
		throw new MyException("Negative size");
		// System.out.println("size="+size);
	}
	public static void main(String[] args) {
		MyExpDemo me= new MyExpDemo();
		try {
			me.arraySize(-5);
			} catch (MyException e) {
			e.printStackTrace();
		}
	}
} 
 
Result:
C:\Exceptions>java MyExpDemo
MyException: Negative size
        at MyExpTest.arraySize(MyExpTest.java:17)
        at MyExpTest.main(MyExpTest.java:26) 

 

 

 

Comments

Post a Comment

Popular posts from this blog

Using javascript pass form variables to iframe src

Image
   Open PDF in Bootstrap Modal Window   This tutorial shows How to pass a JavaScript/jQuery variable to bootstrap modal view and sets it to iframe  src attribute. It passes value dynamically to src attribute of the iframe. When the user clicks a link, it opens the URL in a popup window. This  code shows the PDF in a Model without download option by hiding the toolbar.  To show PDF toolbar in modal, just add #toolbar=1   in the above script. index.php <!DOCTYPE html> <html lang= "en" > <head> <title>Bootstrap Model with PDF Example - coding-zon</title> <meta charset= "utf-8" > <meta name= "viewport" content= "width=device-width, initial-scale=1" > <link rel= "stylesheet" href= "https://cdn.jsdelivr.net/npm/bootstrap@4.6.2/dist/css/bootstrap.min.css" > <script src= "https://cdn.jsdelivr.net/npm/jquery@3.6.1/dist/jquery.slim.
Read more

Creating a new PDF by Merging PDF documents using TCPDF

Image
Merging two PDFs in PHP What is PDF? The Portable Document Format. PDF stands for "Portable Document Format". Essentially, the format is used when you need to save files that cannot be modified but still need to be easily shared and printed. PDF is one of the most commonly used file types around. PDFs generally contain shareable data, such as text or photo documents etc., and are accessible to anyone who has a computer or smartphone. Unlike a Word file, which requires Microsoft Word to view or edit, most browsers will open a PDF. How to merge PDFs? You can merge several documents into one. In PHP, you have a library called TCPDF which allows you to combine one or more PDF documents to one single document. In this article, we will create a new PDF by Merging PDF documents using TCPDF. Download the PDFMerger-tcpdf.zip here. Unzip it and copy it to the PHP server. Copy the PDF files into the same folder that you want to combine. Open the file: merge-pdf-example.php Provide
Read more

Import excel file into mysql in PHP

Image
  Upload Excel file and Import  it into MySQL in PHP  Create a table in some database with given code.   Download Library - extract it, rename the folder to library . Create index.php file with given code in a server. Create excelUpload.php with given code. Create db_config.php . Create one Excel file with some sample data as shown in the below image of Excel file. Create ' uploads ' folder in the same directory. Now start server, run the index.php. Upload a .xls file. If Everything is fine, Excel data inserted in the above created MySQL table - tbl_products . PHP Version:   5.5.11 Folder Structure      Query: CREATE TABLE IF NOT EXISTS `tbl_products` ( `id` int ( 11 ) NOT NULL AUTO_INCREMENT, `productname` varchar ( 100 ) DEFAULT NULL , `description` varchar ( 100 ) DEFAULT NULL , PRIMARY KEY (`id`) )     Top index.php <!DOCTYPE html> <html> <head> <title> coding-zon Demo - Upload Excel to MySQL in PHP </title> <lin
Read more