W1-Course Module-Introduction-to-Java.pdf

MODULE OF INSTRUCTION Introduction to Java This is the first module of the course Computer Programming 2 and it is about introducing Java. In this module we will be discussing the...

MODULE OF INSTRUCTION Introduction to Java This is the first module of the course Computer Programming 2 and it is about introducing Java. In this module we will be discussing the background of Java and the Java technology. We will also discuss the features and phases of Java. Java Background Java was developed in 1991 by a team of engineers called the “Green Team” led by James Gosling and released in 1995 by Sun Microsystems. It was initially called oak after an oak tree that stood outside his office. Java was originally designed to use in embedded chips in various consumer electronic appliances such as toasters and refrigerators. In 1995 its name was changed to Java because a trademark search revealed that Oak was used by Oak Technology and it was also redesigned for developing Web applications. All the Java releases since 2010 is owned by Oracle because they acquire Sun Microsystems in that year. Today Java is everywhere, in any devices and platform, in the Internet and local device, from smart phones to computers, games to business solutions. You can find Java anywhere and Java helps us to have a better future. What is Java Technology? A programming language, Java is a general-purpose programming language that can be used to create all kinds of applications on your computer. Java syntax is mostly derived from C and C++, therefore if you know how to write in C or C++ you could easily write Java programs. Computer Programming 2 1 Week 3-4 Administering Users and Roles A Java platform, it is a software environment where the Java program runs. There are four platforms that Java offers, these are:  Java Standard Edition (Java SE), it is used to develop client- side applications or an application that can run standalone.  Java Enterprise Edition (Java EE), it is used to develop server- side or network applications. There are several technologies that JavaEE offers, such as Java servlets, JavaServer Pages (JSP), and JavaServer Faces (JSF).  Java Micro Edition (Java ME), it is used to develop applications for small devices, such as cell phones, PDA and smart phones.  JavaFX is a platform for creating desktop applications and rich internet applications that run across a wide variety of devices. Phases of Java Program The first phase of a java program is writing your source code in a text editor or IDE (Integrated Development Environment). The text editors that can be used are notepad, vi, sublime, etc. and for the IDE are NetBeans, Eclipse, BlueJ, etc. The written code should be saved with the.java extension. 2 MODULE OF INSTRUCTION After creating the source file, you need to compile it using the javac compiler. This process will produce a compiled file containing bytecodes and with the extension name of.class. Normally the compiler (other programming language like C, C++, etc.) should produce object code (executable program) that is understandable by the processor, however in Java the compiled object is a.class file which contains bytecode that is not readable by your processor. The Java Virtual Machine is responsible in interpreting your.class file. It converts the bytecodes into another code that can be understood by your processor. Since it is interpreted, the code will only be translated everytime you perform operation of you program, unlike compiler all your code will be translated at once. Java Features The main reason why they created Java was to deliver a portable and secured programming language. In addition to these major features, other Java features are the following: 1. Simple 2. Object-Oriented 3. Platform independent 4. Secured 5. Robust 6. Architecture neutral 7. Portable 8. Dynamic 9. High Performance 10. Multithreaded 11. Distributed Computer Programming 2 3 Week 3-4 Administering Users and Roles Simple Java is simple because of the following:  It is easy to learn and the syntax is easy to understand, clean and user-friendly.  The syntax is mostly derived from C and C++ therefore it is easier to learn Java after C or C++. The confusing features of C++ were removed such as pointers, operator overloading etc.  It has Garbage Collector that automatically removed unreferenced or unused objects. One of the problems encountered when writing a program is memory leak or the program consumes too much available memory because the programmer forget to deallocate memory. In Java, you no longer need to deallocate the memory the garbage collection thread is responsible for cleaning your memory. Object Oriented In Java, program focuses on Object that may contain data or attributes and behaviour or methods. Java programs are made out of objects that interact with one another, and it can be easily extended since it is based on Object model. 4 MODULE OF INSTRUCTION Platform Independent A Java program is platform independent, which means you just need to write a program once and run it on many different operating systems. Unlike other programming languages such as C, C++, etc., they are compiled on a specific platform. The Java Virtual Machine or JVM is responsible for making the same program capable of running on multiple platforms. Code Security Java is secured which allow us to develop a program that is free from virus or tampering. Java is secured because of the following features: Computer Programming 2 5 Week 3-4 Administering Users and Roles  Java programs run inside a virtual machine (JVM). The Java Virtual Machine is an abstract machine that is implemented by emulating software on a real machine. Typically the program (created from another language like C) directly interacts with the operating system and if the program is infected with virus, it will definitely affect the operating system, unlike in Java program will not directly run though the operating system.  The Class Loader is responsible for loading classes into Java Virtual Machine. It adds security by separating the package for the classes of the local file system from those that are imported from network sources and classes are verified before it is loaded to JVM.  The Bytecode Verifier is responsible for traversing the bytecode and checking the code fragments for illegal code that can violate access right to object. It checks the bytecodes for the correct number and type of operands, data types are not accessed illegally, the stack is not over or underflowed and that methods are called with the appropriate parameter types. Robust Robust means strong and effective in all or most situations and condition. Java uses strong memory management and automatic garbage collection mechanism. It has no pointers that avoids security problem. There is an exception handling and type checking mechanism. The Java Compiler checks the program for any errors and interpreter checks any run time error. Architecture-neutral Architecture refers to the processor (CPU Architecture), Java programs can run on any processors without considering the architecture or vendor (providers). The languages like C or C++ is 6 MODULE OF INSTRUCTION architecture dependent which means you need to have a separate program for 32-bit and 64-bit Operating System. Portable According to Sun Microsystem: “Portability = Platform Independent + Architecture Neutral” Language Portability is when you can do the WORA ("Write once, run anywhere") program. Java bytecode can be ported to any platform regardless its architecture. It's a combination of platform independence and architectural neutral that makes Java portable. Dynamic Byte code makes Java become dynamic and can adapt to an evolving environment. New features can be easily integrated or the software can be easily extended without creating a new version. High Performance Even though Java is an interpreted language the execution speed of Java programs improved significantly because of just-in-time compilation (JIT). Java is also faster compared to any interpreted language because it uses byte code that is close to native code. Computer Programming 2 7 Week 3-4 Administering Users and Roles Multithreaded Multithreading is a capability of a single program to execute several tasks independently and continuously. Playing music while downloading the video file in one program is an example of multithreading. Multithreading is important for multimedia, network programming etc. Distributed Distributed computing is a model wherein the components of a software are located in multiple networked computers working together to achieve common goals. In this way, it will improve the efficiency and performance of the software. For example, in a 3- tier model, rendering user interface is performed in one computer, another computer conducts reading and writing to the database and business logic is done in another computer. Java allows you to create distributed software, since networking capability is integrated into it. LESSON SUMMARY: In this lesson, you should have been introduced to Java.  Java was developed in 1991 by James Gosling.  Java is a programming language and a platform.  Java code generates bytecodes after compilation and interpreted by JVM. 8 MODULE OF INSTRUCTION  Java is simple, object-oriented, platform independent, secured, robust, architecture neutral, portable, dynamic, high Performance, multithreaded and distributed. Computer Programming 2 9