Java How To Program 8/e PDF

Java How to Program, 8/e 1 2 3  Java application programming  Videos at www.deitel.com/books/jhtp8/ ▪ Help you get started with Eclipse and NetBeans integrated development environments....

Java How to Program, 8/e 1 2 3  Java application programming  Videos at www.deitel.com/books/jhtp8/ ▪ Help you get started with Eclipse and NetBeans integrated development environments. 4  Java application ▪ A computer program that executes when you use the java command to launch the Java Virtual Machine (JVM).  Sample program in Fig. 2.1 displays a line of text. 5 6  Comments // Fig. 2.1: Welcome1.java ▪ // indicates that the line is a comment. ▪ Used to document programs and improve their readability. ▪ Compiler ignores comments. ▪ A comment that begins with // is an end-of-line comment—it terminates at the end of the line on which it appears.  Traditional comment, can be spread over several lines as in ▪ This type of comment begins with. ▪ All text between the delimiters is ignored by the compiler. 7  Javadoc comments ▪ Delimited by. ▪ All text between the Javadoc comment delimiters is ignored by the compiler. ▪ Enable you to embed program documentation directly in your programs. ▪ The javadoc utility program (Appendix M) reads Javadoc comments and uses them to prepare your program’s documentation in HTML format. 8 9 10  Blank lines and space characters ▪ Make programs easier to read. ▪ Blank lines, spaces and tabs are known as white space (or whitespace). ▪ White space is ignored by the compiler. 11 12  Class declaration public class Welcome1 ▪ Every Java program consists of at least one class that you define. ▪ class keyword introduces a class declaration and is immediately followed by the class name. ▪ Keywords (Appendix C) are reserved for use by Java and are always spelled with all lowercase letters. 13  Class names ▪ By convention, begin with a capital letter and capitalize the first letter of each word they include (e.g., SampleClassName). ▪ A class name is an identifier—a series of characters consisting of letters, digits, underscores (_) and dollar signs ($) that does not begin with a digit and does not contain spaces. ▪ Java is case sensitive—uppercase and lowercase letters are distinct—so a1 and A1 are different (but both valid) identifiers. 14 15 16 17  Braces ▪ A left brace, {, begins the body of every class declaration. ▪ A corresponding right brace, }, must end each class declaration. ▪ Code between braces should be indented. ▪ This indentation is one of the spacing conventions mentioned earlier. 18 19 20 21 22  Declaring the main Method public static void main( String[] args ) ▪ Starting point of every Java application. ▪ Parentheses after the identifier main indicate that it’s a program building block called a method. ▪ Java class declarations normally contain one or more methods. ▪ main must be defined as shown; otherwise, the JVM will not execute the application. ▪ Methods perform tasks and can return information when they complete their tasks. ▪ Keyword void indicates that this method will not return any information. 23  Body of the method declaration ▪ Enclosed in left and right braces.  Statement System.out.println("Welcome to Java Programming!"); ▪ Instructs the computer to perform an action  Print the string of characters contained between the double quotation marks. ▪ A string is sometimes called a character string or a string literal. ▪ White-space characters in strings are not ignored by the compiler. ▪ Strings cannot span multiple lines of code. 24  System.out object ▪ Standard output object. ▪ Allows Java applications to display strings in the command window from which the Java application executes.  System.out.println method ▪ Displays (or prints) a line of text in the command window. ▪ The string in the parentheses the argument to the method. ▪ Positions the output cursor at the beginning of the next line in the command window.  Most statements end with a semicolon. 25 26 27 28 29 30  Compiling and Executing Your First Java Application ▪ Open a command window and change to the directory where the program is stored. ▪ Many operating systems use the command cd to change directories. ▪ To compile the program, type javac Welcome1.java ▪ If the program contains no syntax errors, preceding command creates a.class file (known as the class file) containing the platform- independent Java bytecodes that represent the application. ▪ When we use the java command to execute the application on a given platform, these bytecodes will be translated by the JVM into instructions that are understood by the underlying operating system. 31 32 33 34  To execute the program, type java Welcome1.  Launches the JVM, which loads the.class file for class Welcome1.  Note that the.class file-name extension is omitted from the preceding command; otherwise, the JVM will not execute the program.  The JVM calls method main to execute the program. 35 36 37  Class Welcome2, shown in Fig. 2.3, uses two statements to produce the same output as that shown in Fig. 2.1.  New and key features in each code listing are highlighted.  System.out’s method print displays a string.  Unlike println, print does not position the output cursor at the beginning of the next line in the command window. ▪ The next character the program displays will appear immediately after the last character that print displays. 38 39  Newline characters indicate to System.out’s print and println methods when to position the output cursor at the beginning of the next line in the command window.  Newline characters are white-space characters.  The backslash (\) is called an escape character. ▪ Indicates a “special character”  Backslash is combined with the next character to form an escape sequence.  The escape sequence \n represents the newline character.  Complete list of escape sequences java.sun.com/docs/books/jls/third_edition/html/ lexical.html#3.10.6. 40 41 42