Java syntax Floating-point literals A floating-point literal is a number with a decimal point and/or exponent. A floating-point literal is written in either standard or scientific notation. For example, 123.456 is in standard notation, while 1.23456e+2 is in scientific notation. Floating-point literals are stored in the 64-bit double type (the default type), or the 32-bit float type. To store a floating-point literal in the float type, append the letter f or F to the end of the number. Boolean literals A boolean literal represents two possible states: true or false. Boolean literals are stored in the data type boolean. Unlike C/C++ where the states of a Boolean value are represented by 0 (false) and 1 (true), Java represents these states using the keywords true and false. Character literals A character literal represents a single Unicode character. Character literals are always surrounded by single quotes; for example, A and 9 are character literals. Java uses the char type to store single characters. Note The Unicode character set is a 16-bit set that supplants the 8-bit ASCII set. The Unicode set can define up to 65,536 values, which is enough to include symbols and characters from other languages. Check out the Unicode home page at www.unicode.org for more information. Escape sequences A special type of character literal is called an escape sequence. Like C/C++, Java uses escape sequences to represent special control characters and characters that cannot be printed. An escape sequence is represented by a backslash () followed by a character code. The following table summarizes these escape sequences: Character Escape Sequence Backslash \ Backspace b Carriage return r Continuation Double quote Form feed f Horizontal tab t Newline n Octal character DDD Single Quote Unicode character uHHHH 9-4 Learning Java with JBuilder
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Java syntax practice to follow them. The following table lists some of these conventions based on the type of identifier: Type of Identifier Convention Examples Class name The first letter of each word is Mammal, SeaMammal capitalized Function name The first letter of each, except the getAge, setHeight first, word is capitalized Variable name The first letter of each, except the age, brainSize first, word is capitalized Constant names Every letter is capitalized and MAX_HEIGHT, underscores are used between words MAX_AGE Literals A literal, or constant, represents a value that never changes. Think of an identifier as something that represents a value, whereas a literal is a value. For example, the number 35 is a literal; the identifier age represents a number which could be 35. In Java, a literal can be a number (integer or floating-point), a Boolean, a character, or a string. Integer literals Integer literals are written in three formats: decimal (base 10), hexadecimal (base 16), and octal (base 
. Decimal literals are written as ordinary numbers, hexadecimal literals always begin with 0X or 0x, and octal literals begin with 0. For example, the decimal number 10 is 0xA or 0XA in hexadecimal format, and 012 in octal format. An integer literal can be stored in the data types byte, short, int, or long. By default, Java stores integer literals in the int data type, which is restricted to 32-bits. To store an integer literal in the long data type, which can store 64-bit values, add the character l or L to the end of the literal. For example, the literal 9999L is stored as long. The following lines of code use integer literals: int x = 12345; //12345 is a literal int y = x * 4; //4 is a literal In the first line, the literal 12345 is stored directly in the int variable x. In the second line, the literal 4 is used to compute a value first, which in turn is stored in the int variable y. Note that even though an integer literal represents a constant value, it can still be assigned to an integer variable. Think of the variable as a storage unit that at any one time can represent a single literal value. This also applies to the other literal types. Java language basics 9-3
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Java syntax together. The following lists the typical language elements and shows how the language syntax is concerned with these elements: Identifiers: How are variable names composed? What are the naming restrictions and conventions? Literals: How are constant names composed? How are their values assigned? Keywords: What are the language s predefined words? How are they used and how are they not used? Statements: What is a statement and how is one written? Code blocks: How are statements grouped together? Comments: How can the programmer add comments and notes to the program? Expressions: What is an expression and how is one written? Operators: What are the operators used in the language? How are they used in expressions? Can a programmer define his/her own operators? Identifiers An identifier is a name that uniquely identifies a variable, a method, or a class (we will discuss variables later in this chapter; methods and classes are discussed in Chapter 10, Object-oriented programming in Java ). In most languages, there are restrictions on how identifiers are composed. The following lists Java s restrictions on identifiers: All identifiers must begin with a letter, an underscore ( _ ), or a dollar sign ($) An identifier can include, but not begin with numbers An identifier cannot include a white space (tab, space, linefeed, or carriage return) Identifiers are case-sensitive Java keywords cannot be used as identifiers Note Since some C library names begin with an underscore or a dollar sign, it is best to avoid beginning an identifier name with these characters. Importing a C library into a program that uses an underscore or a dollar sign to start an identifier name might cause name clashing and confusion. In addition to these restrictions, certain conventions are used with identifiers to make them more readable. Although these conventions do not affect the compiler in any way, it is considered a good programming 9-2 Learning Java with JBuilder
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C h a p t e r 9 Java language basics This chapter will answer the following questions: What are identifiers, and what are the restrictions on their declaration? What is a literal? What is an escape sequence? What are Java s keywords? What is a code block? What is an expression? What are Java s operators? What data types does Java support? How do Java s data types differ from those of C/C++? What are the looping constructs in Java? What are the conditional statements in Java? Java syntax Before you can effectively read or write programs in any language, you need to know about the language s syntax rules and restrictions. A language s syntax defines the way programs are written in that language; more specifically, the syntax of the language defines the language elements, the way these elements are used, and the way they are used Java language basics 9-1
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Part II Getting Started with Java Getting Started with Java
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Developing international applications Internationalization features in JBuilder These are features of JBuilder Professional and Enterprise. JBuilder includes the following features designed to help you easily create your Java applets and applications for the international marketplace. Multilingual sample application (The IntlDemo.jpr project is located in the samples/jbcl/multilingual directory of your JBuilder installation.) Resource Strings wizard to eliminate hard-coded strings dbSwing internationalization architecture and features UI designer internationalization support Full debugger support for Unicode IDE and compiler support for all JDK native encodings For more information, see Internationalizing programs with JBuilder in Building Applications with JBuilder and the Java documentation at http://java.sun.com/j2se/1.3/docs/guide/intl/index.html. 8-6 Learning Java with JBuilder
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Developing international applications JBuilder applications communicate with database servers through the Java Database Connectivity (JDBC) API, the JavaSoft database connectivity specification. JDBC is the all-Java industry standard API for accessing and manipulating database data. JBuilder database applications can connect to any database using its JDBC driver. JBuilder offers additional tools for developing database applications: JDataStore for data caching and compact persistence Transaction and crash recovery support Advanced concurrency control for increased application performance JDBC 2.0 Type-4 drivers (local and remote) JDataStore Explorer for visually managing DataStores JDBC database tools SQL Builder for visually creating and editing SQL queries to JDBC data sources JDBC Explorer for viewing database data, schema, and creating connections to URLs JDBC Monitor for monitoring SQL applications Data Modules Data Module designer Data Modeler Connection URL Builder For more information, see the Database Application Developer s Guide, the JDataStore Reference available from the Help menu, and the JDataStore Programmer s Guide. For technical questions, visit the database newsgroup on the Borland web page at http://www.borland.com/newsgroups/. Developing international applications As businesses continue to expand into the global marketplace, it is critical to develop applications for the international market. Special features in JBuilder make it easy to take advantage of Java s internationalization capabilities, allowing your applications to be customized for different countries or languages without requiring cumbersome changes to the code. Building distributed applications 8-5
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Building database applications Building database applications These are features of JBuilder Professional and Enterprise. You can use JBuilder s DataExpress components to build all-Java client-server applications, applets, and servlets for the Internet or intranet. With JBuilder Enterprise you can also build JavaServer Pages (JSP). Applications you build in JBuilder are all-Java at runtime and cross-platform. JBuilder allows you to access data and manipulate it using properties, methods, and events defined in the com.borland.dx packages of the DataExpress Component Library in conjunction with the com.borland.dbswing package. By using dbSwing components, you can extend the functionality of Swing components and provide your applications with data-aware capabilities. For more information, see the DataExpress Reference and dbSwing Reference available from the Help menu. JBuilder s modular DataExpress architecture has many benefits, including support for: Network computing Mobile computing Embedded applications Rapid development of user interfaces Using the designer, you can quickly create database applications by dragging and dropping components from the component palette onto your design. 8-4 Learning Java with JBuilder
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Java technologies These are features of JBuilder Enterprise You can also use JBuilder Enterprise to develop both web-based and enterprise applications based on Java 2 Enterprise Edition (J2EE) and these technologies: Common Object Request Broker Architecture (CORBA) CORBA is an open standards-based solution for distributed application development that allows clients and servers to be written in any language that CORBA supports on any platform. For more information, see the tutorial Exploring CORBA-based distributed applications in JBuilder in the Distributed Application Developer s Guide. CORBA interfaces with Java (Caffeine) VisiBroker (included with JBuilder Enterprise edition) incorporates features, collectively known as Caffeine, which enable you to define CORBA interfaces with Java. For more information, see Caffeine: defining CORBA interfaces with Java in the Distributed Application Developer s Guide. Enterprise JavaBeans (EJB) and EJB wizards With JBuilder s suite of EJB wizards, you can visually create Enterprise JavaBeans , the server-side component architecture for the Java platform. EJB wizards also simplify the grouping, testing, and deployment of EJBs by providing visual tools for creating EJB groups, a test client, and 1.1 XML Deployment Descriptors. For more information, see Developing Enterprise JavaBeans (EJB) in the Distributed Application Developer s Guide. JavaServer Pages Use JBuilder s JavaServer Pages wizard to create JavaServer Pages (JSP) quickly, making it easier and faster for you to build web-based applications using your choice of platforms and servers. For more information, see Developing JavaServer Pages in the Distributed Application Developer s Guide. HTML Clients HTML client applications are HTML forms connected to CORBA objects. For more information, see the tutorial Creating an HTML CORBA client application in the Distributed Application Developer s Guide. For more information on using JavaServer Pages, Remote Method Invocation, Enterprise JavaBeans, or CORBA on the Java platform, go to Sun s Java API web site at http://www.sun.com/products-n-solutions/software/api/java.html. Building distributed applications 8-3
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Java technologies private side, while libraries and compiler options are stored in the shared side. InternetBeans Express converts data presentations between HTML and Java. It can extract data from one and turn it into an appropriate format in the other. Java technologies These are features of JBuilder Professional and Enterprise JBuilder provides features that simplify distributed application development using the following technologies: Remote Method Invocation (RMI) With RMI you can create distributed Java-to-Java applications. For more information, see the tutorial Exploring Java RMI-based distributed applications in JBuilder in the Distributed Application Developer s Guide. Servlets Use JBuilder s Servlet wizard to quickly create servlets. These programs are written in the Java programming language, run on a server, and extend server functionality with such advanced features as security, easy database access, and easier integration with Java applets. For more information, see the tutorial Developing servlets in the Distributed Application Developer s Guide. 8-2 Learning Java with JBuilder
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