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Java was created in 1991 by James Gosling and others at Sun Microsystems to be a platform-independent programming language for use in embedded systems. It was designed to be simple, object-oriented, and robust. The key aspects that enabled portability and security were compiling Java code to bytecode that runs on a Java Virtual Machine, rather than producing native machine code. These features, along with its support for multithreading, made Java well-suited for use on the Internet through applets and addressed security and portability issues.
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- 1. The History and Evolution of Java Lecture-1 Tamjid Rahman Faculty Stamford University
- 2. Java • Java is first and foremost a programming language. • Computer language innovation and development occurs for two fundamental reasons: – To adapt to changing environments and uses – To implement refinements and improvements in the art of programming • The development of Java was driven by both elements in nearly equal measure.
- 3. Java’s Lineage • Java is related to C++, which is a direct descendant of C. • Much of the character of Java is inherited from these two languages. • From C, Java derives its syntax. Many of Java’s object oriented features were influenced by C++. In fact, several of Java’s defining characteristics come from—or are responses to—its predecessors. • Each innovation in language design was driven by the need to solve a fundamental problem that the preceding languages could not solve. • Java is no exception.
- 4. The Creation of Java • Java was conceived by James Gosling, Patrick Naughton, Chris Warth, Ed Frank, and Mike Sheridan at Sun Microsystems, Inc. in 1991. • It took 18 months to develop the first working version. • This language was initially called “Oak,” but was renamed “Java” in 1995. • The original impetus for Java was not the Internet! • Instead, the primary motivation was the need for a platform-independent (that is, architecture-neutral) language that could be used to create software to be embedded in various consumer electronic devices, such as microwave ovens and remote controls.
- 5. The Creation of Java (cont…) • Many different types of CPUs are used as controllers. The trouble with C and C++ (and most other languages) is that they are designed to be compiled for a specific target. • Although it is possible to compile a C++ program for just about any type of CPU, to do so requires a full C++ compiler targeted for that CPU. • The problem is that compilers are expensive and time- consuming to create. • An easier—and more cost-efficient—solution was needed. • In an attempt to find such a solution, Gosling and others began work on a portable, platform-independent language that could be used to produce code that would run on a variety of CPUs under differing environments. • This effort ultimately led to the creation of Java.
- 6. How Java Changed the Internet • Java had a profound effect on the Internet. • Besides applet, Java also addressed some of the thorniest issues associated with the Internet: portability and security. • Let’s look more closely at each of these-
- 7. How Java Changed the Internet-Applets (cont…) • An applet is a special kind of Java program that is designed to be transmitted over the Internet and automatically executed by a Java-compatible web browser. • Furthermore, an applet is downloaded on demand, without further interaction with the user. • If the user clicks a link that contains an applet, the applet will be automatically downloaded and run in the browser. • Applets are intended to be small programs. • They are typically used to display data provided by the server, handle user input, or provide simple functions, such as a loan calculator, that execute locally, rather than on the server. • In essence, the applet allows some functionality to be moved from the server to the client.
- 8. How Java Changed the Internet-Applets (cont…) • The creation of the applet changed Internet programming because it expanded the universe of objects that can move about freely in cyberspace. • The applet is a dynamic, self-executing program. Such a program is an active agent on the client computer, yet it is initiated by the server. • As desirable as dynamic, networked programs are, they also present serious problems in the areas of security and portability. • Obviously, a program that downloads and executes automatically on the client computer must be prevented from doing harm. • It must also be able to run in a variety of different environments and under different operating systems. • As you will see, Java solved these problems in an effective and elegant way. Let’s look a bit more closely at each.
- 9. How Java Changed the Internet-Security • Every time we download a “normal” program, we are taking a risk, because the code we are downloading might contain a virus, Trojan horse, or other harmful code. • At the core of the problem is the fact that malicious code can cause its damage because it has gained unauthorized access to system resources. • In order for Java to enable applets to be downloaded and executed on the client computer safely, it was necessary to prevent an applet from launching such an attack. • Java achieved this protection by confining an applet to the Java execution environment and not allowing it access to other parts of the computer. • The ability to download applets with confidence that no harm will be done and that no security will be breached may have been the single most innovative aspect of Java.
- 10. How Java Changed the Internet-Portability • Portability is a major aspect of the Internet because there are many different types of computers and operating systems connected to it. • If a Java program were to be run on virtually any computer connected to the Internet, there needed to be some way to enable that program to execute on different systems. • It is not practical to have different versions of the applet for different computers. • The same code must work on all computers. • Therefore, some means of generating portable executable code was needed. • Java has the same mechanism that helps ensure security also helps create portability.
- 11. Java’s Magic: The Bytecode • The key that allows Java to solve both the security and the portability problems is that the output of a Java compiler is not executable code. Rather, it is 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). • In essence, the original JVM was designed as an interpreter for bytecode. • Many modern languages are designed to be compiled into executable code because of performance concerns. • However, the fact that a Java program is executed by the JVM helps solve the major problems associated with web- based programs.
- 12. Java’s Magic: The Bytecode (cont…) • 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. • The fact that 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. • Because bytecode has been highly optimized, the use of bytecode enables the JVM to execute programs much faster than you might expect. • HotSpot technology provides a Just-In-Time (JIT) compiler for bytecode.
- 13. Java’s Magic: The Bytecode (cont…) • A JIT compiler compiles code as it is needed, during execution. • Furthermore, not all sequences of bytecode are compiled—only those that will benefit from compilation. • The remaining code is simply interpreted. • However, the just-in-time approach still yields a significant performance boost. • Even when dynamic compilation is applied to bytecode, the portability and safety features still apply, because the JVM is still in charge of the execution environment.
- 14. The Java Buzzwords • The key considerations were summed up by the Java team in the following list of buzzwords: – Simple. Java was designed to be easy for the professional programmer to learn and use effectively. Assuming that anyone has some programming experience, (s)he will not find Java hard to master. – Object-Oriented. Although influenced by its predecessors, Java was not designed to be source-code compatible with any other language. This allowed the Java team the freedom to design with a blank slate. One outcome of this was a clean, usable, pragmatic approach to objects. The object model in Java is simple and easy to extend.
- 15. The Java Buzzwords (cont…) –Robust. The ability to create robust programs was given a high priority in the design of Java. To gain reliability, Java restricts us in a few key areas to force us to find our mistakes early in program development. At the same time, Java frees us from having to worry about many of the most common causes of programming errors. Because Java is a strictly typed language, it checks our code at compile time. However, it also checks your code at run time. To better understand how Java is robust, consider two of the main reasons for program failure: memory management mistakes and mishandled exceptional conditions (that is, run-time errors). Memory management can be a difficult, tedious task in traditional programming environments.
- 16. The Java Buzzwords (cont…) – For example, in C/C++, the programmer will often manually allocate and free all dynamic memory. This sometimes leads to problems, because programmers will either forget to free memory that has been previously allocated or, worse, try to free some memory that another part of their code is still using. Java virtually eliminates these problems by managing memory allocation and deallocation for you. (In fact, deallocation is completely automatic, because Java provides garbage collection for unused objects.) Exceptional conditions in traditional environments often arise in situations such as division by zero or “file not found,” and they must be managed with clumsy and hard-to-read constructs. Java helps in this area by providing object-oriented exception handling.
- 17. The Java Buzzwords (cont…) – Multithreaded. Java was designed to meet the real- world requirement of creating interactive, networked programs. To accomplish this, Java supports multithreaded programming, which allows you to write programs that do many things simultaneously. – Architecture-Neutral. A central issue for the Java designers was that of code longevity and portability. The Java designers made several hard decisions in the Java language and the Java Virtual Machine in an attempt to alter this situation. Their goal was “write once; run anywhere, any time, forever.” To a great extent, this goal was accomplished.
- 18. The Java Buzzwords (cont…) – Interpreted and High Performance. Java enables the creation of cross-platform programs by bytecode which was carefully designed so that it would be easy to translate directly into native machine code for very high performance by using a just-in-time compiler. Java run- time systems that provide this feature lose none of the benefits of the platform-independent code. – Distributed. Java is designed for the distributed environment of the Internet because it handles TCP/IP protocols. – Dynamic. Java programs carry with them substantial amounts of run-time type information that is used to verify and resolve accesses to objects at run time. This makes it possible to dynamically link code in a safe and