Exception

Exception  Handling

Exception :
It is a technique of processing problems that occur during the execution of program.

Difference between Exception and Error :
Exception: It is unwanted and unexpected event that disturb the normal flow of program execution.

Error : Something that goes wrong in our application or program that leads to crash your output or logic.


How Exception  Handling Works ?

When  a problem occurs exception object is created, thrown and then handled.

Exception Handling Keyword:

Try- catch
Throw
Throws
Finally

Java Exception Hierarchy:

Types  of Exceptions:

Checked Exception : These are the exceptions that the java compiler enforces you to provide either by using try-catch mechanism or throws declaration mechanism. If this requirement is not met ,the compiler will issue an error messages indicating that the exception must be caught or declared.

Various checked exceptions defined in the java.lang.package are,

1.    ClassNotFoundException

2.    IllegalAccessException

3.    InstantiationException

4.    NoSuchMethodException

Unchecked Exception: These are the exceptions that the java compiler doesnot enforces you to explicity provide in the program code.

Various Unchecked Exceptions are,

1.    ArithmeticException

2.    ArrayIndexOutOfBoundsException

3.    ArrayStoreException

4.    ClassCastException

5.    IllegalArgumentException

6.    NegativeArraySizeException

7.    NullPointerException

8.    NumberFormatException

The java.lang package defines several classes and exceptions.

Exceptions	Description	Checked	Unchecked
ArithmeticException	Arithmetic  Errors such as divide by zero.	-	Yes
ArrayIndexOutOfBoundsException	Array index is not within array.length	-	Yes
ClassNotFoundException	Related Class not found	Yes	-
IOException	Input/Output field not found	Yes	-
IllegalArgumentException	Illegal arguments when calling a method	-	Yes
InterruptedException	One thred has been interrupted by another thread	Yes	-
NoSuchMethodException	Noexistent  method	Yes	-
NullPointerException	Invalid use of null reference	-	Yes
NumberFormatException	Invalid string for conversion to number	-	Yes

Exception Control Flow:

Getting  Information From Exception:

List of Method defined by Throwable  Class.

Methods	Description
String toString( )	Gives you a String object and description of the exception. This  methods is called by the println ( ) method when an object of throwable is passed to it as argument.
String getMessage( )	Gives you the description of the exception in program.
Throwable fillInStackTrace( )	Gives you aThrowable Object that contains a stack trace.
void print StackTrace( )	Gives you and print the stack trace
void printStackTrace(PrintStream stream)	Return the stack trace to a specific defined stream
String getLocalizedMessage	Return the Localized description of the exception

Throw: When you want to throw an exception explicitly , then use throw keyword.

 

Throws: This is  used when you are  not using the try catch statement in your code but you know that this particular class is capable of throwing so and so exception(only checked exceptions). 

Output:

• A new file named test will be created.

Finally: If an exception occur inside a try-catch block and there is no matching catch block, the method terminates without further executing lines of code .
If  you want that lines of code must be executed regardless of whether or not there is matching cathch block, put those lines inside the catch block.

Defining Your Own Exceptions:
You  can create your  own customized exception as per requirements of the application. On each application there is a specific constraints. For this, you create your own customized Exception defining all the constraints and ensure the integrity in the application.