Specifying the Exceptions Thrown by a Method

  • The throws keyword indicates what exception type may be thrown by a method.


  • There are many exception types available in Java: ArithmeticException, ClassNotFoundException, ArrayIndexOutOfBoundsException, SecurityException, etc. 


    •  
public class MyClass {
  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...)
  }
}

How to Throw Exceptions

  • The throw Statement All methods use the throw statement to throw an exception. The throw statement requires a single argument: a throwable object.


  • Throwable objects are instances of any subclass of the Throwable class. Here's an example of a throw statement. 


    •  
throw someThrowableObject;

  • Let's look at the throw statement in context. 


    •  
public class MyClass {
  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...)
  }
}