Tiêu đề Notes 1.pdf ✅

1 The Java Virtual Machine : It is an abstract machine and it is the base for the Java platform and is ported onto various hardware- based platforms. The Java Application Programming Interface (API) : The API is a large collection of ready-made software components that provide many useful capabilities. It is grouped into libraries of related classes and interfaces; these libraries are known as packages. Object Oriented Programming using JAVA UNIT I The History and Evolution of Java What is Java 1. Java technology is both a programming language and a platform. 2. Java is a high level, robust, secured and object-oriented programming language. Java programming language: The Java programming language is a high-level and object-oriented language that can be characterized by all of the following buzzwords / features: i) Simple vii) Portable ii) Object oriented viii) Interpreted iii) Distributed ix) High Performance iv) Multithreaded x) Robust v) Dynamic xi) Secure vi) Architecture Neutral Java Platform: Any hardware or software environment in which a program runs is known as a platform. Since Java has its own runtime environment (JRE-Java Runtime Environment) and API, it is called platform. The Java platform has two components – API and Java Virtual Machine
2 The Creation of Java Java was originally developed to develop a language for digital devices such as set-top boxes and consumer electronic devices such as microwave ovens and remote controls. Java was developed by James Gosling, Patrick Naughton, Mike Sheridan at Sun Microsystems Inc. in 1991. It took 18 months to develop the first working version. The initial name was Oak but it was renamed to Java in 1995. Primary Motivation(s) for Java creation: 1. The primary motivation was the need for a platform-independent (architecture- neutral/portable) language that could be used to create software to be embedded in various consumer electronic devices, such as microwave ovens and remote controls. 2. The second important factor is the World Wide Web / Internet. a) Java is used to develop web based programs / Internet programming. b) The Internet consists of a diverse, distributed universe populated with various types of computers, operating systems, and CPUs. Platform Independence or Architecture Neutral or Portable: (Write Once, Run Anywhere) a) Java is a Platform Independent language. Java sometimes called as “Write Once, Run Anywhere (WORA)” language. b) Java achieves platform independence through bytecode and JVM. Java Program Execution: 1. In the Java programming language, all source code is first written in plain text files ending with the .java extension.
3 Bytecode: Bytecode is a highly optimized set of instructions designed to be executed by the Java run-time system, which is called the Java Virtual Machine (JVM). Java is platform independent but JVM is platform dependent: JVM is platform independent because JVM is designed to each platform separately. 2. Those source files are then compiled into .class files by the javac compiler. 3. A .class file does not contain code that is native to your processor; it instead contains bytecodes — the machine language of the Java Virtual Machine (Java VM). 4. The java launcher tool then runs your application with an instance of the Java Virtual Machine. 5. Through the JVM, the same application is capable of running on multiple platforms. Java’s magic: bytecode 1) Translating a Java program into bytecode makes it much easier to run a program in a wide variety of environments because only the JVM needs to be implemented for each platform. 2) Although the details of the JVM will differ from platform to platform, all understand the same Java bytecode. 3) A Java program is executed by the JVM also helps to make it secure. Because the JVM is in control, it can contain the program and prevent it from generating side effects outside of the system.