Can constructor methods send back a value like other methods?


No, because there's no way to receive that value. Unlike other methods that can be used as part of an equation, the argument of a method, or other statements, constructors are only handled in response to a new statement. There's no way for that statement to receive a value that would be sent by the method.


Do you have to create an object to use class variables or methods?


Because class variables and methods aren't associated with a specific object, you don't need to create an object solely for the purpose of using them. The use of the Integer.parseInt() method is an example of this because you don't have to create a new Integer object just to convert a string to an int value.


Is there a list of all the built-in methods that Java supports?


Sun offers full documentation for all classes in the Java language, including all public methods you can use. The documentation is in HTML format, so you can browse easily through the classes to see what methods and variables they include. Visit the Java 2, version 5 documentation web page at http://java.oracle.com/j2se/1.5/docs/api. During the preparation of this tutorial, I spent enough time at this part of Sun's website to qualify for California residency.


When I run the VirusLook app without an argument, the program crashes with an ArrayIndexOutOfBoundsException error. What can I do to correct this?


This error occurs because of the effort to call the Integer.parseInt() method with a null string as the value of arguments[0]. One solution would be to test the value of arguments[0] with an if statement and call Integer.parseInt() only if arguments[0] is not null. This would require a default value for the numViruses variable. Arguments often require some kind of testing to make sure they have acceptable values before you use them.


What's the difference between the Integer object and the int variable type?


The first is an object, and the second is a simple variable type. Each of the variable types, such as char, int, and float, has a corresponding object. The object is used when you want to make use of an object's methods or treat the variable like an object. Because an Integer object can do things in a program that the int variable type cannot, it is convenient to have both.


What is the systematic IUPAC name for a carboxylic acid with a potassium ion in place of the acid hydrogen?


Potassium octanoate, a corrosive acid for which there is no known practical use. IUPAC, the International Union of Pure and Applied Chemistry, is a scientific council that recommends names for chemicals, atomic weights, and related areas of study. In 1997, the group participated in the decision to name atomic element 106 seaborgium after Berkeley nuclear physicist Glenn Seaborg.