Slide 10.6: Exceptions (cont.): The throw keyword

Slide 10.5: Exceptions (cont.): The finally keyword
Slide 10.7: Checked vs unchecked exceptions
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Exceptions (Cont.)

The throw Keyword
The throw statement allows you to create a custom error. The throw statement is used together with an exception type. There are many exception types available in Java, for example,

ArithmeticException, which is thrown when an exceptional arithmetic condition has occurred
ClassNotFoundException, which is thrown when an application tries to load a class, but no definition for the class with the specified name could be found
ArrayIndexOutOfBoundsException, which is thrown to indicate that an array has been accessed with an illegal index
SecurityException, which is thrown by the security manager to indicate a security violation

The exception type is often used together with a custom method. The following program throws an exception if age is below 18 (print “Access denied!”). If age is 18 or older, print “Access granted!”:

ThrowDemo.java (with a throw keyword)

public class ThrowDemo {
  public static void main( String[ ] args ) {
    checkAge( Integer.parseInt( args[0] ) );
  }
  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!" );
  }
}

shell> java ThrowDemo

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Slide 10.5: Exceptions (cont.): The finally keyword
Slide 10.7: Checked vs unchecked exceptions
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