Lab#1 (14/3/1431h) Introduction To java programming cs425

1. Lab#1 (14/3/1431h)Introduction To java programming cs425 Prepared By: I.RaniahAlghamdi

2. About Java • Java (with a capital J) is a high-level, third generation programming language. • Java is most similar to C++ in syntax. • Java has considerably more functionality than C, primarily because of the large class library. • It is platform independent programming language (Write once, run every where) : • The Java compiler produces a special format called byte code. • Java byte code can run on any Java Virtual Machine (JVM) regardless of computer architecture • Byte code still need an interpreter to execute them on any given platform (ex: Sun's program java (with a little j)) . CPIT 425, Spring 2010

3. Java is Simple and Safe • Java was designed to make it much easier to write bug free code by: • keeping the language simple. • It is automatic memory management. • Java uses an automatic garbage collector to manage memory in the object lifecycle. • There are no pointers in Java. • Java programs cannot access arbitrary addresses in memory. CPIT 425, Spring 2010

4. Java is Simple and Safe • Java has strong typing • Variables must be declared • Casts are strictly limited to casts between types that make sense. int to a long √ byte to a short √ long to a booleanX int to a String. X • implements a robust exception handling mechanism • Java enabled web browser checks the byte codes of an applet to verify that it doesn't do anything nasty before it will run the applet. CPIT 425, Spring 2010

5. Most special in Java • Java lets you write special programs called applets that can be downloaded from the Internet and played safely within a web browser. • Traditional computer programs : • have far too much access to your system (downloaded and executed) • Even more dangerous software would be promulgated if any web page you visited could run programs on your system. • Java solves this problem by restricting what an applet can do. • A Java applet cannot write to your hard disk without your permission. • It cannot write to arbitrary addresses in memory and thereby introduce a virus into your computer. • It should not crash your system. CPIT 425, Spring 2010

6. Java is Object-Oriented • An Object : it consists of state and related behavior. An object stores its state in fields and exposes its behavior through methods. • A Class : it is the blueprint from which individual objects are created. • Inheritance: Object-oriented programming allows classes to inherit commonly used state and behavior from other classes. use the extends keyword, followed by the name of the class to inherit from: class subClassextendssuperClass CPIT 425, Spring 2010

7. Java is Object-Oriented Cont. • Interface: just like classes except that they use the word interface instead of class and is restricted to containing method declarations without bodies. Interface interface_name { } And to use the interface in the class definition: Public class class_name implements interface_name { } • A package: is a namespace that organizes a set of related classes and interfaces. The Java platform provides an enormous class library (a set of packages). This library is known as the "Application Programming Interface", or "API“. CPIT 425, Spring 2010

8. Language Basics • Variables • Instance Variables (Non-Static Fields) • Class Variables (Static Fields) • Local Variables (method’s variables) • Parameters • Primitive Data Types: byte, short, int, long, float, double, boolean, char. • Arrays CPIT 425, Spring 2010

9. Java Development Kit (JDK) • (JDK) is a Sun Microsystems product aimed at Java developers. • Some of JDK contents: • java – The loader for Java applications. This tool is an interpreter and can interpret the class files generated by the javac compiler. • javac – The compiler, which converts source code into Java bytecode • jar – The archiver, which packages related class libraries into a single JAR file. • jdb – The debugger • appletviewer – This tool can be used to run and debug Java applets without a web browser. CPIT 425, Spring 2010

10. Reading from a file • For writing a java program to read file line by line: • Use import java.io.*; • DefineFileInputStreamobject to obtain input bytes from a file in a file system (to open the file). • Define DataInputStream object to let an application read primitive Java data types from an underlying input stream in a machine-independent way. • Define InputStreamReader object which is used as a bridge from byte streams to character streams. CPIT 425, Spring 2010

11. Reading from a file Cont. • Define BufferedReaderobject to Read text from a character-input stream, buffering characters so as to provide for the efficient reading of characters, arrays, and lines. • Read File Line By Line using readLine() method of BufferedReaderobject. • Close the input stream. CPIT 425, Spring 2010

12. Need to do… • Practice to write to a file… You will need that later in your HWs. • For writing to a file, you will need to use FileOutputStreamobject. CPIT 425, Spring 2010

13. Good References • http://java.sun.com/docs/books/tutorial/java/index.html GOOD LUCK  CPIT 425, Spring 2010