Hardcore Java

Chapter 5. Exceptional Code

The common attribute of all exceptional code is, not surprisingly, the proper use of exceptions. Exceptions can give your code immense debugging power and provide a base for indicating user errors. At one time, using exceptions for business logic errors was considered to be bad form. Instead of throwing an exception, the programmer was encouraged to use deeply nested if statements to catch user errors. Java has changed this perspective somewhat through the use of two types of exceptions, both of which are covered extensively in this chapter.

Two Types of Exceptions

Java started out by borrowing the C++ exception mechanism. However, early in the development of the JDK, Sun made some important modifications. Instead of only one category of exception, Java has two. Today, Java differentiates between an Exception and a RuntimeException. To understand how this differentiation is advantageous, you must first understand these two types of exceptions.

The Exception Subclasses

When a method can throw an Exception , the exception must be caught in the body of the method or declared in the throws clause of the method declaration:

public void someDatabaseMethod ( ) throws SQLException {
  // Do some JDBC Work.
}

In this code, the method someDatabaseMethod( ) can throw a SQLException if there is a problem with the database. Since SQLException is a descendant of the Exception class, someDatabaseMethod( ) must either handle the exception with a try-catch block or declare ...