Frequently Ask Questions
Q: I have heard about a special type of Java program called a servlet. What is it?
A: A servlet is a small program that executes on the server. Just as applets dynamically extend the functionality of a web browser, servlets dynamically extend the functionality of a web server. It is helpful to understand that as useful as applets can be, they are just one half of the client/server equation. Not long after the initial release of Java it became obvious that Java would also be useful on the server side. The result was the servlet. Thus, with the advent of the servlet, Java spanned both sides of the client/server connection. Although the creation of servlets is beyond the scope of this beginner’s guide, they are something that you will want to study further as you advance in Java programming. (Coverage of servlets can be found in my book Java: The Complete Reference, published by Oracle Press/McGraw-Hill.)
Q: To address the issues of portability and security, why was it necessary to create a new computer language such as Java; couldn’t a language like C++ be adapted? In other words, couldn’t a C++ compiler that outputs bytecode be created?
A: While it would be possible for a C++ compiler to generate something similar to bytecode rather than executable code, C++ has features that discourage its use for the creation of Internet programs—the most important feature being C++’s support for pointers. A pointer is the address of some object stored in memory. Using a pointer, it would be possible to access resources outside the program itself, resulting in a security breach. Java does not support pointers, thus eliminating this problem.
Q: You state that object-oriented programming is an effective way to manage large programs. However, it seems that it might add substantial overhead to relatively small ones. Since you say that all Java programs are, to some extent, object-oriented, does this impose a penalty for smaller programs
A: No. As you will see, for small programs, Java’s object-oriented features are nearly transparent. Although it is true that Java follows a strict object model, you have wide latitude as to the degree to which you employ it. For smaller programs, their “object-orientedness” is barely perceptible. As your programs grow, you will integrate more object-oriented features effortlessly.
Q: Why does Java have different data types for integers and floating-point values? That is, why aren’t all numeric values just the same type?
A: Java supplies different data types so that you can write efficient programs. For example, integer arithmetic is faster than floating-point calculations. Thus, if you don’t need fractional values, then you don’t need to incur the overhead associated with types float or double. Second, the amount of memory required for one type of data might be less than that required for another. By supplying different types, Java enables you to make best use of system resources. Finally, some algorithms require (or at least benefit from) the use of a specific type of data. In general, Java supplies a number of built-in types to give you the greatest flexibility.
Q: Does the use of a code block introduce any run-time inefficiencies? In other words, does Java actually execute the { and }?
A: No. Code blocks do not add any overhead whatsoever. In fact, because of their ability to simplify the coding of certain algorithms, their use generally increases speed and efficiency. Also, the { and } exist only in your program’s source code. Java does not, per se, execute the { or }.
Q: You say that there are four integer types: int, short, long, and byte. However, I have heard that char can also be categorized as an integer type in Java. Can you explain?
A: The formal specification for Java defines a type category called integral types, which includes byte, short, int, long, and char. They are called integral types because they all hold whole-number, binary values. However, the purpose of the first four is to represent numeric integer quantities. The purpose of char is to represent characters. Therefore, the principal uses of char and the principal uses of the other integral types are fundamentally different. Because of the differences, the char type is treated separately in this book
Q: Why does Java use Unicode?
A: Java was designed for worldwide use. Thus, it needs to use a character set that can represent all the world’s languages. Unicode is the standard character set designed expressly for this purpose. Of course, the use of Unicode is inefficient for languages such as English, German, Spanish, or French, whose characters can be contained within 8 bits. But such is the price that must be paid for global portability.
Q: Is a string consisting of a single character the same as a character literal? For example, is “k” the same as ‘k’?
A: No. You must not confuse strings with characters. A character literal represents a single letter of type char. A string containing only one letter is still a string. Although strings consist of characters, they are not the same type.
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