Java Exception Handling

There is always the possibility of errors occurring during the normal flow of a programme in any programming language. Handling the errors is known as Exception Handling.

We use try/catch block to handle exceptions.

You can specify a set of codes to be tested for errors inside the try statement and catch block containing the code to be executed if any error occurs.

Syntax for try/catch block

try
{
  // set of codes to try
}
catch(Exception ex)
{
  // codes to handle error
}

Example for try/catch block

  public class Main {
  public static void main(String[ ] args) {
    try {
      int[] numbers = {4,5,6};
      System.out.println(numbers[5]);
    } catch (Exception e) {
      System.out.println("Index out of range.");
    }
  }
}

Output

Index out of range.

Finally Statement

The finally block is executed irrespective of try or catch block execution.

Example for finally statement

public class Main {
  public static void main(String[ ] args) {
    try {
      int[] numbers = {4,5,6};
      System.out.println(numbers[5]);
    } catch (Exception e) {
      System.out.println("Index out of range.");
    }
    finally{
        System.out.println("End of try-catch block");
    }
  }
}

Throw Exception

With the help of throw keyword it is possible to create custom error.

Example for throwing error and handling it

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

  }

  public static void main(String[] args) {
    checkAge(15);
  }
}

Output

java.lang.Exception: Access denied - You must be at least 18 years old.