Java Programming, Second Edition Chapter One Creating Your First Java Program

In this chapter, you will:  Learn about programming  Understand object-oriented programming concepts  Learn about the Java programming language  Start a Java program  Add comments to a Java program  Run a Java program  Modify a Java program

Learning about programming  Program - A set of instructions that you write to tell a computer what to do  Machine language - The language a machine works in  High-level programming languages - Languages that allow programmers to use terms such as “read,” “write,” and “add”  Syntax-The rules of the language  Logic – correct statements and order to produce outcome desired

Converting high level-language code  Compiler - All instructions converted at once from high-level language to machine language; new program is then run  C/C++, COBOL, FORTRAN, etc. compile  Interpreter - High-level language code is read and converted at run time line by line  Basic, Perl, PHP, Python are interpreted  Java is compiled, then interpreted

Procedural Programming  Procedural programming – step-by-step approach to problem-solving  Variables – hold values  Operations – read, write, math  Procedures are groups of operations  Calls – when a program jumps to a procedure

OOP Concepts  OOP is a different approach to problem- solving; conceptualizing objects instead of steps  Create objects, then applications that use these objects  Similar to concrete objects in the real world  Objects have states and methods  States are also called attributes  Methods are functions – blocks of code

OOP Concepts cont.  Class – a group of objects with common properties  Instance – single existing object of a class  Inheritance – objects inherit attributes from the parent class  Encapsulation – “data hiding”; programmer only needs to know the interface for a class, not its internal workings

Java Programming Language  Developed by Sun Microsystems as an object-oriented language that is both used for general-purpose business programs and for interactive World Wide Web-based Internet programs

Architecturally Neutral  The Java programming language can be used to write a program that will run on any platform or operating system using the JVM (Java Virtual Machine).  Java runs on a hypothetical computer known as the Java virtual machine (JVM)  When your source code program is compiled into byte code, an interpreter within the JVM interprets the byte code and interfaces with the operating system to produce the program results

Java Program Types  Java applets – programs embedded in a Web page  Java applications – stand-alone programs  Applications can be  Console-based: DOS-style input/output from keyboard to screen, or  Windowed – GUI interface

Starting a Java Program  Literal string- A series of characters that will appear exactly as entered  Arguments- Information that a method requires to perform its task System.out.println(“First Java Program”);

Java class name requirements  Must begin with a letter of the alphabet, [or an underscore, or a dollar sign]  Can only contain letters, digits, underscores, or dollar signs  Cannot be a Java reserved keyword  Cannot be one of the following values: true, false, or null

Printing a String  Access Modifier- Defines the circumstances under which a class can be accessed  static- Ensures that the method is accessible even though no objects of the class exist  void- The method does not return any value when it is called

Program Comments  Program Comments- Nonexecuting statements that you add to a program for the purpose of documentation  Line comments- //  Block comments - /* */  javadoc comments - /** */

Running a Java Program 1. You must compile the program you wrote (called the source code) into bytecode. 2. You must use the Java interpreter to translate the bytecode into executable statements.

Running a Java Program  The commands for compiling and executing are:  Compiling a program (from the DOS prompt)  javac Hello2.java  Executing a program  java Hello2

Modifying a Program  To produce the new output:  Modify the text file that contains the existing program  Change the class name  Change the literal string that currently prints and then add an additional text string

Errors  Run-time or Logic Errors- Occur when the syntax of the program is correct and the program is compiled, but produces incorrect results  Syntax Errors- Programming errors that occur when you introduce typing errors into your program

Documentation  has full Java documentation of every class, method, and attribute in the Java libraries, plus tutorials and more