Exception handling in Java

An exception is an unwanted or unexpected event that occurs during the execution of the program that disrupts the normal flow.

class Test
{
    public static void main(String[] args)
    {
        System.out.println("1");
        System.out.println("2");
        System.out.println("3");
        System.out.println("4");
        System.out.println("5");
        System.out.println(10/0);
        System.out.println("6");
        System.out.println("7");
    }
}

Output is printed only upto 5 and an arithmetic exception is shown

Difference between exception and error

Hierarchy of Exception

There are two types of exceptions in Java

• Checked exception/Compile time exception

• Unchecked exception/Run time exception

Exception keywords in Java

Whenever there is an exception, the method in which it occurs will create an object with the following properties:

• exception name

• description

• stack trace

We can get the exception as output using

1. e.printStackTrace();

   prints exception name, stack trace and description

2. SOP(e); // SOP(e.toString());

   prints exception name and description

3. SOP(e.getMessage());

   prints only decription

1. Try catch

//syntax
try
{
    //risky code
}
catch(ExceptionClassName ref.var.name)
{
    //handling code
}

class Test
{
    public static void main(String[] args)
    {
        try
        {
            int a=10,b=0,c;
            c=a/b;
        }
        catch(Exception e)
        {
            System.out.println(e);
        }
    }
}

2. Finally

Finally is the block that is always executed whether an exception is handled or not

class Test
{
    public static void main(String[] args)
    {
        try
        {
            int a=10,b=0,c;
            c=a/b;
        }
        catch(Exception e)
        {
            System.out.println(e);
        }
        finally
        {
            System.out.println("finally block");
        }
    }
}

3. Throw

public class Main {
  static void checkAge(int age) {
    if (age < 18) {
      throw new ArithmeticException("Access denied - You must be at least 18 years old.");
    }
    else {
      System.out.println("Access granted - You are old enough!");
    }
  }

  public static void main(String[] args) {
    checkAge(15); // Set age to 15 (which is below 18...)
  }
}

4. Throws

public class Main {
  static void checkAge(int age) throws ArithmeticException {
    if (age < 18) {
      throw new ArithmeticException("Access denied - You must be at least 18 years old.");
    }
    else {
      System.out.println("Access granted - You are old enough!");
    }
  }

  public static void main(String[] args) {
    checkAge(15); // Set age to 15 (which is below 18...)
  }
}