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CHAPTER-1(Introduction to Java)                                                  Bottom

 

History of java

Java was devoloped by James Gosling, Patrick Naughton, Chris Warth, Ed Frank, and Mike Sheridan at Sun Microsystems, Inc. in 1991.This language was initially called oak but was renamed in 1995.The original purpose for developing Java was not the Internet! Instead, the primary motivation was the need for a platform-independent (that is, architectureneutral) language that could be used to create software to be embedded in various consumer electronic devices, such as microwave ovens and remote controls. As you can probably guess, 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.


 

Features of Java

1.SIMPLE:- Java was designed to be easy for the professional programmer to learn and use effectively. If you already understand the basic concepts of object-oriented programming, learning Java will be even easier JAVA inherits many features from c /c++ and c# languages. Besides these similarities JAVA  has many ways of accomplishing a given task.

2.Object-Oriented:- Java is object oriented because java treats everything in terms of objects.We manage our programme code in a hierarchy of objects which is easy to handle as compare to non object oriented programming languages like C, COBOL ,PASCAL etc.

3. Robust:-JAVA provides robustness by executing the applications on different  platform successfully .Also  Java is a strictly typed language, it checks your code at compile time. However, it also checks your code at run time. Exceptional handling and automatic memory management are two main concepts to provide robustness.

4. Multithreaded:-JAVA provides a multithreading concept with the help of which we can perform many tasks simultaneously .It saves time and executes application faster in comparison to multithreaded programming.

5. Architecture-Neutral (Plateform Independent):- Java  provides our  program longevity and portability .The programmes written in java are based on “ WRITE ONCE  RUN ANY WHERE” . We only need "JVM" to run our programme on our operating system.

6. Portability:- Many types of computers and operating systems are in use throughout the world and many are connected to the Internet. For programs to be dynamically downloaded to all the various types of platforms connected to the Internet, some means of generating portable executable code is needed

7.Security:- JAVA also provides security by prohibiting the malicious programmes to access the critical resourses.

 



 

JVM (JAVA VIRTUAL MACHINE)

The key that allows Java to solve both the security and the portability problems just described 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).JVM is an interpreter for bytecode.the fact that a Java program is executed by the JVM helps solve the major problems associated with downloading programs over the Internet ,because in order to run a program a JVM is required and every operating system has an inbuilt java virtual machine so java applications can be run from anywhere in the world.

Bytecode is a compiled code of the java program , which is then interpreted by the Java Virtual Machine.The fact that a Java program is interpreted also helps to make it secure. Because the execution of every Java program is under the control of the JVM.The use of bytecode enables the Java run-time system to execute programs much faster

 


JIT(JUST IN TIME)

Java was designed for interpretation, compilation of bytecode into native code. Along these lines, Sun supplies its Just In Time (JIT) compiler for bytecode, which is included in the Java 2 release. When the JIT compiler is part of the JVM, it compiles bytecode into executable code in real time, on a piece-by-piece, demand basis. It is important to understand that it is not possible to compile an entire Java program into executable code all at once, because Java performs various run-time checks that can be done only at run time. Instead, the JIT compiles code as it is needed, during execution. 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 run-time system (which performs the compilation) still is in charge of the execution environment. Whether your Java program is actually interpreted in the traditional way or compiled on-the-fly, its functionality is the same.



Note :
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