Error and Exception

Error : 

• Mistake that cant be handle or recover using programming logics.
• In java it is a sub-class of Throwable Interface.

Type of Errors:

• Syntax Error
• Logical Error
• Runtime Error

Syntax Error:

Errors that arise to avoid  the rules or structure of the language have not been followed. They are detected by the compiler.

Logical Error:

Errors that occur when a program doesn't perform the way it was intended to.

Runtime Error:

Errors that occur while the program is running if the environment detects an operation that is impossible to carry out.

Some typical causes of errors:

• Memory errors (i.e. memory incorrectly allocated, memory leaks,OutOfMemory)
• File system errors (i.e. disk is full, disk has been removed)
• Network errors (i.e. network is down, URL does not exist)
• Calculation errors (i.e. divide by 0)

Exception:

It is the unexpected condition that arise during the program compilation or execution .

It terminates the program compilation or execution abnormally.

It can be handle using programming mechanism (exception handling).

Type of Exception:

• Compile-Time Exception or Checked Exception
• Run-Time Exception or UnChecked Exception

Compile-Time Exception(Checked Exception):

• Exception that arise during the compilation of program,in this type of exception compiler forced to deal with exception .
• It  inherited from the core Java class Exception. They represent exceptions that are frequently considered “non fatal” to program execution.
• Checked exceptions must be handled in our code, or passed to parent classes for handling.

Run-Time Exception(UnChecked Exception):

• Exception that arise during execution of program and that terminates execution flow abnormally.
• It doesn't stop compiler to create .class(byte code).
• It can be handle using exception handling mechanism.

Exception Hierarchy:

Some Checked Exception are:

Some Checked Exception are:

Exception Handling Mechanism:

Java provide some exception handling blocks and clause for handle the exception.

  These are............

• try

• catch

• finally

• throw 

• throws

Use of exception handling mechanism:

In above method, generated exception is catchd inside catch block.

In above method  ,throws IO-Exception is used to declare exception and throw is used to throw exception.

Declaring exceptions:

• Every method must state the types of checked exceptions it might throw. This is known as declaring exceptions.

     

    Example:

         public void myMethod()  throws IOException

         public void myMethod()  throws IOException, OtherException

Throwing exceptions:

When the program detects an error, the program can create an instance of an appropriate exception type and throw it. This is known as throwing an exception. 

Example:

        throw new TheException();

        TheException ex = new TheException();
        throw ex;

        

        or

         throw new Exception();

Catching exceptions:

• It catch the generated exception and show the type of exception,line number where exception is generated,and file in which exception is generated using the method printStackTrace().

try {

  statements;  // Statements that may throw exceptions

}

catch (Exception1 e1) {

//  statements;

}

catch (Exception2 e2) {

//  statements;

}

catch (ExceptionN en) {

  //statements

}

//in Jdk-7 catch can have multiple-parameters

catch( final NullPointerException | ArithmeticException e)

{

e.printStackTrace();

}

Common Exception in Java Programming:

• NullPointerException
• ArithmeticException
• NumberFormatException
• FileNotFoundException
• ClassNotFoundException
• ArrayIndexOutOfBoundsException
• etc..............

Exception Handling with method Overriding:

  The Overriding method can throw:

• No exception
• One or more of the exceptions thrown by the overridden method.
• 
  

  The Overriding method cant throw:

• Additional exceptions not thrown by the overridden method.
• Super-Classes of the exceptions thrown by the overridden method.
• It cant throw any checked exception when overridden method doesn't declare any exception,in this it allow to declare only unchecked exception.

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