CT 229. CT229 Lecture Notes. Labs. Tutorials. Lecture Notes. Programming II CT229. Objectives for CT229. IT Department NUI Galway

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1 Lecture Notes CT 229 Programming II Lecture notes, Sample Programs, Lab Assignments and Tutorials will be available for download at: Lecturer: Dr Ted Scully IT Department NUI Galway Note: Downloading lecture notes is not a substitute for attendance at lectures. Additional material will be covered in lectures that does not appear in the lecture notes. Any Problems -> Edward.Scully@nuigalway.ie 09/09/2006 CT229 09/09/2006 CT229 1 CT229 Labs 2-Semester Course: Regular Lab Assignments Practical Lab Exam (December) Tutorials Marks awarded for lab assignments and lab exam ~20% for assignments/lab exam, rest for written exam Lab Sessions: 2 hours/week BSc(IT) Weds Lab101 (4-6) BSc(P&A) Weds Lab101 (4-6) BE(EE) Thurs Lab101 (4-6) BE(E&CE) Thurs Lab101 (4-6) Labs start on Weds 13 th of Sept 09/09/2006 CT /09/2006 CT229 3 Tutorials Objectives for CT229 Tutorials: 1hr/week BSc(IT) Thurs IT203 (12-1) BSc(P&A) Thurs IT203 (12-1) BE(EE) Tues AC213 (12-1) BE(E&CE) Tues AC213 (12-1) Tutorials will commence in a few weeks Build on your knowledge of programming languages Provide you with a comprehensive understanding of the features of the Java programming language Provide you with experience of developing Java programs Show you how 'real world' algorithms and data structures are implemented and used in Java Introduce you to professional software coding techniques 09/09/2006 CT /09/2006 CT

2 Other Details Course Content (1) Recommended Reading: "Data Structures and Algorithms In Java", Goodrich & Tamassia, Wiley Java: How to Program, Deitel & Deitel, Prentice Hall (General-purpose Java book) Numerous online resources and examples ( Others: see library Notes and lectures! Overview of the Java language Syntax (Compared to C) Object Oriented Programming Composition, Inheritance, Polymorphism Interfaces and Abstract Classes Techniques to Analyse Algorithms Using Recursion List-Based Data Structures Queues; Stacks; Linked lists 09/09/2006 CT /09/2006 CT229 7 Course Content (2) What is Java Hash Tables Hashing functions; Collision processing Comparisons with other data structures Good Programming Practice Sorting and Searching Algorithms Trees Binary trees; tree algorithms; depth-first and breadthfirst searching; balanced trees; AVL trees Priority Queues and Heaps Introduction to Graphs Java is a high-level, third generation programming language Syntax based on C/C++ Designed by Sun Microsystems Publicly announced in 1995 Launch of Java coincided with increase in popularity of WWW Sun decided to apply Java technology to downloadable behaviour for Web browsers and servers Clearly a matter of the right capability being available at the right time! 09/09/2006 CT /09/2006 CT229 9 Turning a Java Program into Machine Code Compiling a Java Program All source code is first written in plain text files ending with the.java extension Source files are then compiled into.class files by the javac compiler A.class file does not contain code that is native to your processor; it instead contains bytecodes Java Interpreter (called Java Virtual Machine) converts bytecode into machine code Happens every time you run program Need different JVM for each type of architecture: run-time executable, available on almost all platforms 09/09/2006 CT /09/2006 CT

Running a Java Program Java Virtual Machine 09/09/2006 CT229 12 09/09/2006 CT229 13 The Java Platform What is the Java Application Programming Interface (API)?

It provides many useful capabilities for a java program such as file handling, graphics etc. (Can be thought of as a larger version of the.

3 Running a Java Program Java Virtual Machine 09/09/2006 CT /09/2006 CT The Java Platform What is the Java Application Programming Interface (API)? Java Platform consists of The Java Virtual Machine The Java Application Programming Interface (API) The Java API is a large software library that can be utilized by any Java program. It provides many useful capabilities for a java program such as file handling, graphics etc. (Can be thought of as a larger version of the.h libraries in the C programming language) It is grouped into libraries of related classes and interfaces; these libraries are known as packages. API Specification can be found on (for example api spec for J2SE can found at ) 09/09/2006 CT /09/2006 CT What are the advantage of using the Java Programming Language? What are the advantages of Java? Simple Object-oriented Safe Multi-Threaded Platform Independent High Performance 09/09/2006 CT /09/2006 CT

4 Java is Simple Java is Object Oriented A language that can be easily programmed without extensive programmer experience. Easy to interpret written code Syntax is straightforward and similar to that of C/C++ The fundamental concepts of Java technology are easily understood. Therefore, programmers can be productive from the very beginning. Employs automatic memory allocation and deallocation. No more alloc, free functions ( It is estimated that half of the bugs in C and C++ occur due to the allocation and deallocation of memory). The Object Oriented paradigm provides a level of abstraction for programmers. Programmers can conceptualise and implement code in terms of objects. In object-oriented programs data is represented by objects. Objects have two sections: Fields (instance variables) are the attributes of an object. They tell you what an object is. Methods tell you what function and object can perform 09/09/2006 CT /09/2006 CT Java is Safe Java is Multi-Threaded One of the primary objectives of java was to provide a programming language that would be secure from outside interference Java provides security within the language and the run-time system. Unlike C/C++, Java programs can t arbitrarily access addresses in memory. Garbage collector automatically deallocates memory when it is no longer needed. Java implements robust exception handling. That is, the execution of a program can catch and handle errors without crashing the program. Java provides the means to build applications with many concurrent threads of activity. A single java program may spawn multiple processes that share CPU time, giving the impression that these processes are running in parallel. Therefore a single Java program can have many different threads executing independently and continuously. Multi-threaded enabled applications can be difficult to construct and debug!! 09/09/2006 CT /09/2006 CT Java is Platform Independent Java is Platform Independent As previously mentioned a.java file is compiled by the javac compiler into a.class file, which contains bytecode. The java virtual machine (JVM) can then translate this into the executable machine code. Because the JVM is available for many different operating systems, the same.class files are capable of running on Microsoft Windows, the Solaris Operating System (Solaris OS), Linux, etc.. Write once, run anywhere This means the.class file is platform independent. I can run the same.class file on any platform that has a JVM. 09/09/2006 CT /09/2006 CT

High Performance Applications and Applets Java byte codes can be compiled on the fly to code that rivals C++ in speed using a just-in-time compiler A just-in-time compiler Bytecode compilation is the

5 High Performance Applications and Applets Java byte codes can be compiled on the fly to code that rivals C++ in speed using a just-in-time compiler A just-in-time compiler Bytecode compilation is the first step, reducing source code to a portable and optimizable intermediate representation When the code is executed, the JVM translates it into native machine code. This can be done on a per-file or per-function basis: functions can be compiled only when they are about to be executed (hence the name "just-in-time"). With Java, you can write Applications and Applets Applications: Standard, stand-alone programs Require a main() method in your code Applets: Programs embedded in a Web browser Web browser performs function of virtual machine Run by viewing a HTML page that has a link to the applet: downloaded along with text & graphics Run automatically on download: potential security risk! Limited functionality: e.g. disk access Applets are written to adhere to specific requirements: details later 09/09/2006 CT /09/2006 CT A Simple Java Program Explanation /* Simple Java program that prints a Hello message */ /* Ted Scully, Sept 2006 */ public class Hello { public static void main(string[] args) { System.out.println("Hello World!"); /* Simple Java program that prints a Hello message */ /* Ted Scully, Sept 2006 */ Comments: ignored by Java compiler public class Hello Begins a class definition Every Java program has at least one public class Body of the class is contained between { and public static void main(string[] args) Begins a method definition Every Java program has a method called main Definition of main method is always just like this 09/09/2006 CT /09/2006 CT Explanation Java Syntax V s C Syntax When program is run, it starts by executing commands in main, in sequence In this program, only 1 line in main The body of main is between { and Note: these parentheses are nested inside the others System.out.println("Hello World!"); Writes Hello World! to the system standard output When you run this program from the Command Prompt, the line is displayed in it First marks the end of main definition Second marks the end of Hello class definition 09/09/2006 CT /09/2006 CT

6 Writing a Program Compiling and Running Use a text editor Notepad, Textpad, EditPlus, other... Save the file as Hello.java File name must be same as main class name The extension is always.java Important: Java is case-sensitive (like C) Programs themselves, commands, file names Use indentation Put a tab at the start of lines inside the first { 2 tabs for lines inside 2 sets of { Appropriate spaces and indentation improve code legibility Java Developers Kit (JDK) Downloadable from Sun javac - Java Compiler java - Java Interpreter (for standalone programs) javadoc - Java Document Generator javah - C File Generator javap - Java class disassembler jdb - Java Debugger appletviewer - Useful if you have no WWW browser These are all console (DOS) programs Graphical Java development environments also available 09/09/2006 CT /09/2006 CT Compiling and Running Basic Java Development To begin: Open a Command Prompt window Change to the directory containing your program (e.g. cd c:\myprogs) To compile your Java program: javac Hello.java Include the file extension Any compilation errors will be displayed with line numbers This produces Hello.class (bytecode) To run it: java Hello Leave off the.class extension As you have seen in the previous slides you need three separate tools to develop a basic java program. You need a tool to: Write the source code (Notepad, Textpad, etc.) Compile that source code into java bytecode (javac compiler) Execute the bytecode (java) Alternative: Write, compile and execute your java code in one program called an IDE (Integrated Development Environment) 09/09/2006 CT /09/2006 CT Java IDE Second Java Program IDE: Integrated Development Environment Editor, compiler, debugger, etc. Graphical user interface Aid productivity Some IDE s Borland JBuilder Symantec VisualCafe Microsoft Visual J++ Blue J ( Eclipse ( Program to Calculate Employee s Total Week s Wages: 1.Look up the employee s pay rate (rate) 2.Determine the number of hours worked (hrs) in week 3.If no. of hours worked < or = 40 then regular wages (wage) = hrs*rate and overtime pay (over) = 0 4.If hrs > 40 then wage = 40*Rate and overtime pay (over) = hrs - 40) * (1.5 * rate) 5.Total Wages (total) = wage + over 09/09/2006 CT /09/2006 CT

7 The Program The Program import javax.swing.joptionpane; // Dialog box methods public class Wages { public static void main(string[] args) { double rate, hrs, over, wage, total; String ratestr, hoursstr; /* Get data in string form: convert to double */ ratestr = JOptionPane.showInputDialog("Enter Hourly Rate:"); rate = Double.parseDouble(rateStr); hoursstr = JOptionPane.showInputDialog("Enter Hours Worked:"); hrs = Double.parseDouble(hoursStr); if (hrs <= 40) { wage = rate * hrs; over = 0; else { wage = rate * 40; over = (hrs - 40) * 1.5 * rate; total = wage + over; JOptionPane.showMessageDialog (null, Total weekly wages are " + total); System.exit(0); // Terminate program 09/09/2006 CT /09/2006 CT Main Features import javax.swing.joptionpane; Loads classes from Java API that program will use javax.swing is a graphical user interface package JOptionPane is a class in package for displaying msg boxes double rate, hrs, over, wage, total; String ratestr, hoursstr; Declares existence of four variables that can hold numerical data ( double-precision floating-point ), and two variables that can hold string (i.e. text) data ratestr = JOptionPane.showInputDialog("Enter Hourly Rate:"); Invokes a method called showinputdialog, which is part of the JOptionPane class (defined javax.swing package) Displays input box with text Enter Hourly Rate ratestr is set to whatever text the user types in Main Features rate = Double.parseDouble(rateStr); parsedouble is a method in Double class, that converts text ( 123 ) to a double number (123.0) Double is a class defined in the Java language package (java.lang); imported automatically if (hrs <= 40) Code to make a decision: which lines will be executed next depends on the data in the variable called hrs Exactly like C total = wage + over; Sets total equal to the sum of wage and over This line is after the if-block; it is executed after whichever of the previous blocks of code is executed 09/09/2006 CT /09/2006 CT Main Features JOptionPane.showMessageDialog (null, "Total weekly wages are " + total); Method that displays a message box Two arguments: 1: usually null 2: the text to display The + joins text; automatically converts numbers to text command (statement) can be split over more than one line The ; indicates the end of a statement System.exit(0); Method of the System class: terminates the program Required for graphical programs Like Double, System is part of java.lang package, which is imported automatically at the start of the program 09/09/2006 CT

CT 229 Fundamentals of Java Syntax

CT 229 Fundamentals of Java Syntax 19/09/2006 CT229 New Lab Assignment Monday 18 th Sept -> New Lab Assignment on CT 229 Website Two Weeks for Completion Due Date is Oct 1 st Assignment Submission is online