![Common scenarios where exceptions
may occur
Scenario where NumberFormatException occurs
The wrong formatting of any value, may occur NumberFormatException.
Suppose I have a string variable that have characters, converting this
variable into digit will occur NumberFormatException.
String s="abc";
Scenario where ArrayIndexOutOfBoundsException occurs
If you are inserting any value in the wrong index, it would result
ArrayIndexOutOfBoundsException as shown below:
int a[]=new int[5];
a[10]=50; //ArrayIndexOutOfBoundsException
9](https://image.slidesharecdn.com/exceptionhandlinginjava-180403090205/85/Exception-handling-in-java-9-320.jpg)
![Java catch block
Java catch block is used to handle the Exception. It must be used after the try
block only.
You can use multiple catch block with a single try.
public class Testtrycatch2{
public static void main(String args[]){
try{
int data=50/0;
}catch(ArithmeticException e){System.out.println(e);}
System.out.println("rest of the code...");
}
}
12](https://image.slidesharecdn.com/exceptionhandlinginjava-180403090205/85/Exception-handling-in-java-12-320.jpg)
![java throw keyword example
public class TestThrow1{
static void validate(int age){
if(age<18)
throw new ArithmeticException("not valid");
else
System.out.println("welcome to vote");
}
public static void main(String args[]){
validate(13);
System.out.println("rest of the code...");
}
}
18](https://image.slidesharecdn.com/exceptionhandlinginjava-180403090205/85/Exception-handling-in-java-18-320.jpg)
![Java Exception propagation
public static void main(String args[]){
TestExceptionPropagation1 obj=new TestExceptionPropagation1();
obj.p();
System.out.println("normal flow...");
}
}
20](https://image.slidesharecdn.com/exceptionhandlinginjava-180403090205/85/Exception-handling-in-java-20-320.jpg)
Exception handling in java
- 1. Exception Handling in Java MADE BY : POOJA ROY 1
- 2. Exception Handling in Java The exception handling in java is one of the powerful mechanism to handle the runtime errors so that normal flow of the application can be maintained. In this page, we will learn about java exception, its type and the difference between checked and unchecked exceptions. 2
- 3. What is exception Dictionary Meaning: Exception is an abnormal condition. In java, exception is an event that disrupts the normal flow of the program. It is an object which is thrown at runtime. Exception Handling is a mechanism to handle runtime errors such as ClassNotFound, IO, SQL, Remote etc. 3
- 4. Advantage of Exception Handling The core advantage of exception handling is to maintain the normal flow of the application. Exception normally disrupts the normal flow of the application that is why we use exception handling. Let's take a scenario: statement 1; statement 2; statement 3; statement 4; statement 5;//exception occurs statement 6; statement 7; statement 8; statement 9; statement 10; Suppose there is 10 statements in your program and there occurs an exception at statement 5, rest of the code will not be executed i.e. statement 6 to 10 will not run. If we perform exception handling, rest of the statement will be executed. That is why we use exception handling in java. 4
- 5. Hierarchy of Java Exception classes 5
- 6. Types of Exception here are mainly two types of exceptions: checked and unchecked where error is considered as unchecked exception. The sun microsystem says there are three types of exceptions: Checked Exception Unchecked Exception Error 6
- 7. Difference between checked and unchecked exceptions ) Checked Exception The classes that extend Throwable class except RuntimeException and Error are known as checked exceptions e.g.IOException, SQLException etc. Checked exceptions are checked at compile-time. 2) Unchecked Exception The classes that extend RuntimeException are known as unchecked exceptions e.g. ArithmeticException, NullPointerException, ArrayIndexOutOfBoundsException etc. Unchecked exceptions are not checked at compile-time rather they are checked at runtime. 3) Error Error is irrecoverable e.g. OutOfMemoryError, VirtualMachineError, AssertionError etc. 7
- 8. Common scenarios where exceptions may occur Scenario where ArithmeticException occurs If we divide any number by zero, there occurs an ArithmeticException. int a=50/0;//ArithmeticException Scenario where NullPointerException occurs If we have null value in any variable, performing any operation by the variable occurs an NullPointerException. String s=null; System.out.println(s.length());//NullPointerException 8
- 9. Common scenarios where exceptions may occur Scenario where NumberFormatException occurs The wrong formatting of any value, may occur NumberFormatException. Suppose I have a string variable that have characters, converting this variable into digit will occur NumberFormatException. String s="abc"; Scenario where ArrayIndexOutOfBoundsException occurs If you are inserting any value in the wrong index, it would result ArrayIndexOutOfBoundsException as shown below: int a[]=new int[5]; a[10]=50; //ArrayIndexOutOfBoundsException 9
- 10. Java Exception Handling Keywords There are 5 keywords used in java exception handling. try catch finally throw throws 10
- 11. Java try block Java try block is used to enclose the code that might throw an exception. It must be used within the method. Java try block must be followed by either catch or finally block. Syntax of java try-catch try{ //code that may throw exception }catch(Exception_class_Name ref){} Syntax of try-finally block try{ //code that may throw exception }finally{} 11
- 12. Java catch block Java catch block is used to handle the Exception. It must be used after the try block only. You can use multiple catch block with a single try. public class Testtrycatch2{ public static void main(String args[]){ try{ int data=50/0; }catch(ArithmeticException e){System.out.println(e);} System.out.println("rest of the code..."); } } 12
- 13. output Exception in thread main java.lang.ArithmeticException:/ by zero rest of the code... 13
- 14. Internal working of java try-catch block 14
- 15. Java finally block Java finally block is a block that is used to execute important code such as closing connection, stream etc. Java finally block is always executed whether exception is handled or not. Java finally block follows try or catch block. 15
- 16. Java finally block 16
- 17. Java throw keyword The Java throw keyword is used to explicitly throw an exception. We can throw either checked or uncheked exception in java by throw keyword. The throw keyword is mainly used to throw custom exception. We will see custom exceptions later. The syntax of java throw keyword is given below. 17
- 18. java throw keyword example public class TestThrow1{ static void validate(int age){ if(age<18) throw new ArithmeticException("not valid"); else System.out.println("welcome to vote"); } public static void main(String args[]){ validate(13); System.out.println("rest of the code..."); } } 18
- 19. Java Exception propagation class TestExceptionPropagation1{ void m(){ int data=50/0; } void n(){ m(); } void p(){ try{ n(); }catch(Exception e){System.out.println("exception handled");} } 19
- 20. Java Exception propagation public static void main(String args[]){ TestExceptionPropagation1 obj=new TestExceptionPropagation1(); obj.p(); System.out.println("normal flow..."); } } 20
- 21. Java Exception propagation 21
- 22. Java Exception propagation In the above example exception occurs in m() method where it is not handled,so it is propagated to previous n() method where it is not handled, again it is propagated to p() method where exception is handled. Exception can be handled in any method in call stack either in main() method,p() method,n() method or m() method. 22
- 23. Java throws keyword The Java throws keyword is used to declare an exception. It gives an information to the programmer that there may occur an exception so it is better for the programmer to provide the exception handling code so that normal flow can be maintained. Exception Handling is mainly used to handle the checked exceptions. If there occurs any unchecked exception such as NullPointerException, it is programmers fault that he is not performing check up before the code being used. 23
- 24. Difference between throw and throws in Java throw Java throw keyword is used to explicitly throw an exception. Checked exception cannot be propagated using throw only. Throw is followed by an instance. Throw is used within the method. You cannot throw multiple exceptions. throws Java throws keyword is used to declare an exception. Checked exception can be propagated with throws. Throws is followed by class. Throws is used with the method signature. You can declare multiple exceptions e.g. public void method()throws IOException,SQLException. 24
- 25. Thank you 25