Exception Handling in Java

Introduction to Exceptions:

• In the process of compilation and execution of Java application, chance of getting 3 types of errors (Syntax, Logical and Runtime).
• Exception is a Runtime Error.
• Exception is a class.
• Exception causes abnormal termination of program.
• Exception need to be handled.

Compile time errors: A syntactical error occurs when we violate programming language rules while writing programs.

class Check
{
	static
	{
		static int a=10 ; //Error: local variable cannot be static
	}
}

Some more examples:

• Every method should have return type
• Abstract and final cannot be combined.
• Class cannot be private.

Logical errors: The result is unexpected if the program is logically in correct. Compiler and JVM will not generate any error message in case of logical error.

class LogicalError 
{
	public static void main(String[] args) 
	{
		int a=5 , b=2 ;
		float c = a/b; (int / int = int)
		float c = (float)a/b ;  (float / int = float)
		System.out.println("Result : "+c);
	}
}

Runtime errors:

• It is called Exception.
• Violation of JVM rule gives Exception.
• A programmer need to analyze all the situations which can generate errors while application is running.
• Exception needs to be handled at runtime but logic must be implemented at compile time.
• Exception logic executes only when the problem has risen at runtime.

• Programmer need to define code for success and failure cases.
• Failure case always raises exception.
• Runtime error causes:
  • Abnormal termination of program
  • Informal information to End user.

import java.util.Scanner;
class ReadInt 
{
	public static void main(String[] args) 
	{
		Scanner scan = new Scanner(System.in);
		System.out.print("Enter ATM PIN : ");
		int pin = scan.nextInt();
		System.out.println("PIN is : " + pin);
	}
}

Compile the code: