Java Tutorial

Java Tutorial Java Features C++ vs Java Java History Java Hello World Java Development Kit Java Runtime Environment Java Virtual Machine Difference between JDK, JRE, and JVM Memory Areas in Java Java Operators Java Keywords Primitive Data Types Variables

Java Loops

Java Do While Loop Java While Loop Java For Loop Java Enhanced For Loop

Java Programs

Java Basic Programs Factorial Program in Java Fibonacci Series Program in Java Prime Number Program in Java Palindrome Number Program in Java Armstrong Number Program in Java Anagram Program in Java Pattern Programs in Java Calculator Program in Java Leap Year Program in Java Addition Program in Java Number Pattern Programs in Java Star Pattern Programs in Java Package Program in Java Pyramid Program in Java Sorting Program in Java String Palindrome Program in Java Even Odd Program in Java For Loop Program in Java If Else Program in Java Switch Case Program in Java GCD Program in Java LCM Program in Java Hello Program in Java Matrix Program in Java Menu Driven Program in Java Series Program in Java Client Server Program in Java Swapping Program in Java Pig Latin Program in Java Tower of Hanoi Program in Java Recursion Program in Java Matrix Multiplication Program in Java Perfect Number Program in Java Classes and Objects in Java Example Programs String Programs in Java Array Programs in Java Constructor Program in Java Inheritance Program in Java Abstract class Program in Java Interface Program in Java Encapsulation Program in Java Polymorphism Program in Java Exception Handling Program in Java Multithreading Program in Java Thread Program in Java Collection Programs in Java ArrayList Program in Java Stack Program in Java Applet Program in Java Swing Program in Java JDBC Program in Java How to run Java program in command prompt How to run Java program in Eclipse

Java Sorting

Sorting Algorithms in Java Merge Sort in Java Quick Sort in Java Bubble Sort in Java Insertion Sort in Java Selection Sort in Java Heap Sort in Java Radix Sort in Java Topological Sort in Java Bucket Sort in Java Counting Sort in Java

Java OOPs Concepts

OOPs - Object Oriented Programming Objects and Classes in Java Java Naming Conventions Constructors in Java Java this keyword Java static keyword Inheritance in Java Aggregation in Java Java super keyword Constructor Chaining and Constructor Overloading Java Polymorphism Static and Dynamic Binding in Java Java Abstraction Abstract class in Java Interface in Java Difference between Abstract class and Interface Java final keyword Packages in Java Access Modifiers in Java Java Wrapper classes Java Numbers Java Characters Java Integer Java Boolean Java Arrays Java Command Line Arguments Java strictfp Keyword Java Math

Java Strings

Java Strings Java String Methods StringBuilder in Java StringBuffer in Java Java Regular Expressions StringBuffer vs StringBuilder String vs StringBuffer String vs StringBuilder String Manipulation in Java Java String Concatenation How to Reverse a String in Java String Array in Java How to Compare Two Strings in Java How to Concatenate Two Strings in Java Why String in Immutable in Java java.lang.NumberFormatException for Input String String Pool in Java Java Generate Random String How to take String Input in Java Java String Interview Questions

Java Exceptions

Exception Handling in Java Java try catch Java throw Java throws Difference between throw and throws Java finally Java Custom Exception Java Exception Propagation

Garbage Collection

Automatic Resource Management in Java Java Garbage Collection Java finalize() Java gc() Difference between final, finally and finalize

Multithreading

Multithreading in Java Process and Thread in Java Basic Terms in Multithreading Java Thread creation Thread Scheduler in Java Java Thread class DeadLock in Java

Java IO

Java IO Java Read File Java BufferedWriter Java InputStreamReader Java File Java Read File Line By Line Java FileOutputStream Jar File in Java

Serialization

Java Serialization Java transient

Networking

Java Network Programming Java Socket Programming Java URL Java URLConnection HttpURLConnection in Java Java InetAddress Java DatagramSocket and Java DatagramPacket

AWT

Java AWT

Swing

Swing in Java

Java Collections

Collections in Java Java List Interface ArrayList in Java LinkedList in Java Vector in Java Stack in Java ArrayList vs LinkedList in Java ArrayList vs Vector in Java Java Set Interface HashSet in Java LinkedHashSet in Java TreeSet in Java Java Queue Interface PriorityQueue in Java ArrayDeque in Java Java Map Interface HashMap in Java LinkedHashMap in Java TreeMap in Java Dictionary in Java Hashtable in Java Properties in Java Collections class in Java Java Comparable Java Comparator Comparable vs Comparator in Java

Java Generics

Generics in Java

Java Annotations

Annotations in Java

Java JDBC

Java JDBC Tutorial

Java Differences

Java vs JavaScript Python vs Java Kotlin vs Java Java vs C++ C# vs Java Static vs Non-static in Java C vs Java int vs Integer in Java Stack vs Heap in Java Java Array vs ArrayList

How to

How to run Java program How to set path in Java How to check the Java version in cmd How to install Java in Windows 10 How to run Java program in cmd How to call a method in Java How to sort an array in Java How to iterate HashMap in Java How to write Java program How to create an array in Java How to create a package in Java How to generate random numbers in Java How to input String in Java How to create thread in Java How to find length of String in Java How to sort a string in Java How to use scanner in Java How to achieve multiple inheritance in Java How to run Java program in Eclipse How to call a function in Java How to create array of objects in Java How to create custom exception in Java How to achieve abstraction in Java How to call static method in Java

Java 8 Features

Java 8 Features Lambda Expressions in Java Functional Interface in Java Streams in Java Java Base64 Encoding and Decoding Parallel Arrays Sort in Java

Java 9 Features

Java 9 Tutorial Java 9 Try With Resources Java 9 Interface Private Method

Java Servlet Tutorial

Java Servlets Tutorial

Java JSP Tutorial

Java JSP Tutorial

Hibernate Tutorial

Hibernate Tutorial

Spring Tutorial

Spring Tutorial

Spring MVC Tutorial

Spring MVC Tutorial

Jenkins Tutorial

Jenkins Tutorial

Java Math Methods

Math.abs() Math.acos() Math.addExact() Math.asin() Math.atan () Math.atan2() Math.cbrt() Math.ceil() Math.copysign() Math.cos() Math.cosh() Math.decrementExact() Math.exp() Math.expm1() Math.floor() Math.floorDiv() Math.floorMod() Math.getExponent() Math.hypot() Math.IEEEremainder() Math.incrementExact() Math.log() Math.log10() Math.log1p() Math.max() Math.min() Math.multiplyExact() Math.multiplyFull() Math.negateExact() Math.nextAfter() Math.nextDown() Math.nextUp() Math.pow() Math.random() Math.rint() Math.round() Math.scalb() Math.signum() Math.sin() Math.sinh() Math.sqrt() Math.subtractExact() Math.tan() Math.tanh() Math.toDegrees() Math.toIntExact() Math.toRadians() Math.ulp()

Java String Methods

toCharArray() copyValueOf() endsWith() equals() equalsIgnoreCase() format() getBytes() getChars() hashCode() indexOf() intern() isEmpty() join() lastIndexOf() length() replace() replaceAll() replaceFirst() split() startsWith() subSequence() substring() toLowerCase() toUpperCase() trim() valueOf()

Java Conversion

Java Convert String to int Java Convert int to String Java Convert String to long Java Convert long to String Java Convert String to float Java Convert float to String Java Convert String to double Java Convert double to String Java Convert String to Date Java Convert Date to String Java Convert String to Object Java Convert Object to String Java Convert String to char Java Convert char to String Java Convert int to long Java Convert long to int

Misc

Functional Interfaces in Java Singleton class in Java Awesome explanation of Strings in Java Object class in Java Static class in Java All the important string methods in Java String Handling Method in Java What are Array strings in Java Advantages and Disadvantages of Strings in Java Big Decimal class in Java Class definition in Java Char and String differences in Java Difference between String, StringBuffer and StringBuilder in java Replace character in string Java String Coding Interview Questions in Java What is String in Java? String isnullorempty in Java String Matches in Java Trim Method in String Java Bean class in Java Libraries in Java Arithmetic Operations on String in Java Convert Char array to string in java Check whether Java is installed or not How to calculate time difference in Java How to stop execution after a certain time in Java Jagged Array in Java Java ArraylistRemove() Time Complexity Java Swing Time Picker Zigzag Array in Java

Exception Handling in Java

Before looking at how exceptions are handled in java, it is necessary to see what an exception is.

What is Exception?

Whenever a program is written, errors are encountered. Some of these errors are displayed at compile time and they demand to be corrected for the programs to run. Some of the errors do not show up at compile time but disrupts the normal flow of execution at run time. These errors are known as Exceptions in programming. "An exception is an unwanted condition that occurs at run time and disrupts the normal flow of execution of the code." An exception can also be thought as a run time error. The program with an exception is compiled successfully but not run. Exceptions occur when the operation initiated by the programmer is not valid. Most common types of exception are:
  • Division by zero.
  • Accessing an element of an array that is out of bound.
  • Trying to add a value in an array of the type not defined.
  • Accessing an element of a string that is out of bound.
  • Declaring array size as negative.
  • Etc.
When exceptions occur in the code, a sufficient mechanism is needed to handle it; else the program will not get executed smoothly. Java provides a mechanism to handle exceptions using five keywords namely; try, catch, throw, throws and finally. "Java exception is an object that describes the occurrence of an exception in the java code."

Types of exception:

We have three types of exception in java they are:
  1. Checked Exceptions: These exceptions are extended from the java.lang.Exception class and are handled in the body of code itself using the try and catch blocks.These exceptions occur at compile time and without handling them, the program cannot be executed further. E.g. File not found, SQL and IO exception.
  2. Unchecked Exceptions: These exceptions are extended from the java.lang.RuntimeException class and are not essentially handled in the code. Java Virtual Machine (JVM) handles such exceptions. These exceptions occur at run time. E.g. Index out of bound, division by zero, etc.
  3. Errors: They are the exceptions that cannot be handled in normal circumstances. They are usually created in response to catastrophic failure. E.g. Stack Overflow, out of memory error, virtual machine error, etc.

How to handle Exceptions?

The exception is handled in java by using 5 keywords:
  1. Try
  2. Catch
  3. Finally
  4. Throws
  5. Throw

1. Try and catch

Whenever a programmer feels that a block of code can throw some exception that section of code is written under the try block and set of operations to be performed after the exception is caught, written under the catch block. The catch block catches the exception thrown by the try block. A try block should always be followed by at least one catch block. Syntax of try and catch block:
try
{
.....................
..................... // code which is expected to throw an exception.
}
catch(Exception-name e)
{
.........................
......................... // process to handle the exception.
}
 

Program to illustrate the use of try and catch blocks

class Excep
{
public static void main(String args[])
{
int x,y;
try
{
x=0;
y=5567/5*x;
System.out.println("Result is"+y);
}
catch (ArithmeticException e)
{
System.out.println("Division by zero exception is encountered:"+e);
}
}
}
Output:
Division by zero exception is encountered: java.lang.ArithmeticException

Illustrating the use of multiple catch blocks.

In some cases, more than one exception can be thrown by a block of code. To handle multiple exceptions being thrown, we can use multiple catch blocks.
Syntax for using multiple catch blocks:
try
{
.............
}
catch(Exception-type1 e)
{ 
..............
}
catch(Exception-type2 e)
{ 
...............
}
catch(Exception-type N e)
{ 
...............
}
Program to show how multiple catch blocks are used within a program
class multicatch
{
public static void main(String args[])
{
int ar[] =new int[2];
ar[0]=5;
ar[1]=10; int b=5;
try
{
int x = ar[1]/b-ar[0];
System.out.println("The result of operation is"+x);
System.out.println("8th element of array is"+ar[7]);
}
catch(ArithmeticException e)
{
System.out.println("Divide by zero exception occurred"+ae);
}
catch(ArrayIndexOutOfBoundsException e) 
{
System.out.println("Element does not exist"+e);
}
catch(Exception e)
{
System.out.println("Exception occurred"+e);
}
}
In the above program, we have caught the main Exception class in the end and its specific cases are mentioned above. This is because all the specific exceptions are defined under the main exception class and if we use it at the very first place then the other catch statements will never be executed and we will get a compile time error stating; 'second catch statement is unreachable'.

2. Finally

Finally statement is usually written after the try and catch block. No matter whether any exception is thrown in the program or not, finally block always gets executed. For this reason, we use the finally block when we want a series of steps to always get executed. It can also be used to handle the exception that is not caught by the catch statement previously, or that is thrown by the try block. Each try block should have at least one catch or finally statement.
Syntax of finally
try
{
.........
}
catch(exception-type e)
{
..........
}
finally
{
...........
}

Program to illustrate the use of finally statement

class multicatch
{
public static void main(String args[])
{
int ar[] =new int[2];
ar[0]=5;
ar[1]=10; int b=5;
try
{
int x = ar[1]/b-ar[0];
System.out.println("The result of operation is"+x);
System.out.println("8th element of array is"+ar[7]);
}
catch(ArithmeticException e)
{
System.out.println("Divide by zero exception occurred"+ae);
}
catch(ArrayIndexOutOfBoundsException e) 
{
System.out.println("Element does not exist"+e);
}
catch(Exception e)
{
System.out.println("Exception occurred"+e);
}
finally
{
int z= ar[1]/ar[0];
System.out.println("Result is"+z);
}
}
}

3. Throw

With the help of throw keyword, it is possible for the programmer to explicitly throw an exception that is not defined in the Java run time system. The syntax of throw statement is-
throw throwableInstance;
Here, throwableInstance much be an
  • Object of Throwable class
  • Subclass of Throwable class
There are two ways of obtaining a throwable object:
  • Using a parameter in catch clause.
  • Creating an object with new keyword.
When throw keyword is encountered in the code, the normal flow is disrupted. The code is inspected try block, inspected to see if it has a catch statement to handle the exception, subsequently all the try blocks are checked, if no catch block is found then the exception is handled by the default exception handler.

Code to illustrate the use of throw keyword

class NewException extends Exception
{
NewException(String txt)
{
super(txt);
}
}
class TestNewException
{
public static void main(String args[])
{
int x = 1000000, y=1;
try
{
int z = x/y;
if(z>1000)
{
throw new NewException("Result is too large then desirable");
}
}
catch(NewException e)
{
System.out.println("User defined exception caught");
System.out.ptintln(e.getMessage());
} 
finally
{
System.out.println("This program was declined due to uncertain termination");
}
}
}

4. Throws

  • Throws keyword is used with the method declaration to let the user know that the method can throw an exception of the specified type.
  • Throws keyword is used when the method might throw an exception but there is no mechanism to handle the exception.

Program to illustrate the use of throws keyword

class ExcepLast
{
void divide() throws ArithmeticException
{
int a =55, b=0, c;
c = a/b;
}
public static void main(String args[])
{
try
{
divide();
}
catch(ArithmeticException e)
{
System.out.println("Exception is successfully caught"+e);
}
}
}

Difference Between Throw and Throws

Throw Throws
Throw is used to explicitly throw an exception. Throws is used to let the users know about the exception that might be thrown by a method.
Throw keyword is followed by an instance. Throws keyword is followed by a class.
Throw keyword is used within a method. Throws keyword is used with the method signature.
Multiple exceptions cannot be explicitly thrown. Multiple exceptions can be declared.
Propagation of checked exception is not possible. Propagation of checked exception is possible.


Difference between error and exception

Error Exception
An error is detected at compile time. Exception is detected at run time.
An error cannot be recovered. Exception can be recovered.
Errors are defined under the java.lang.Error package. Exceptions are defined under the java.lang.Exception package.
Errors cannot be handled by the program code. Exceptions can be handled in the program code.
Errors are defined as unchecked type. Exceptions are defined as checked as well as unchecked type.
e.g. missing semicolon, missing variable declaration, etc. e.g. dividing an integer by zero, accessing element that is out of bound, etc.



ADVERTISEMENT
ADVERTISEMENT