Web server certificate - Chapter 2 Introduction to Java Applications 59 Software
Chapter 2 Introduction to Java Applications 59 Software Engineering Observation 2.1 Avoid using identifiers that contain dollar signs ($), as the compiler often uses dollar signs to create identifier names. In Chapter 2 through Chapter 7, every class we define begins with the public keyword. For now, we will simply require this keyword. The public keyword is discussed in detail in Chapter 8. Also in that chapter, we discuss classes that do not begin with keyword public. [Note: Several times early in this text, we ask you to mimic certain Java features we introduce as you write your own Java programs. We specifically do this when it is not yet important for you to know all of the details of a feature in order for you to use that feature in Java. All programmers initially learn how to program by mimicking what other programmers have done before them. For each detail we ask you to mimic, we indicate where the full discussion will be presented later in the text.] When you save your public class definition in a file, the file name must be the class name followed by the .java file-name extension. For our application, the file name is Welcome1.java. All Java class definitions are stored in files ending with the file-name extension .java. Common Programming Error 2.3 It is an error for a public class if the file name is not identical to the class name (plus the .java extension) in terms of both spelling and capitalization. Therefore, it is also an error for a file to contain two or more public classes. Common Programming Error 2.4 It is an error not to end a file name with the .java extension for a file containing an application s class definition. If the extension is missing, the Java compiler will not be able to compile the class definition. A left brace (at the end of line 4), {, begins the body of every class definition. A corresponding right brace (in line 13 in this program), }, must end each class definition. Notice that lines 6 11 are indented. This indentation is one of the spacing conventions mentioned earlier. We define each spacing convention as a Good Programming Practice. Good Programming Practice 2.6 Whenever you type an opening left brace, {, in your program, immediately type the closing right brace, }, then reposition the cursor between the braces to begin typing the body. This practice helps prevent errors due to missing braces. Good Programming Practice 2.7 Indent the entire body of each class definition one level of indentation between the left brace, {, and the right brace, }, that define the body of the class. This format emphasizes the structure of the class definition and helps make the class definition easier to read. Good Programming Practice 2.8 Set a convention for the indent size you prefer, and then uniformly apply that convention. The Tab key may be used to create indents, but tab stops may vary between editors. We recommend using three spaces to form a level of indent. Common Programming Error 2.5 If braces do not occur in matching pairs, the compiler indicates an error. Copyright 1992 2002 by Deitel & Associates, Inc. All Rights Reserved. 7/2/01
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