Editions or Flavors of Java:-
When Java was originally released in 1996, it was just java and no such thing as “editions” was there. but as use of Java increased, then in 1999 SUN categorized it into 3 editions called J2SE, J2EE and J2ME.
Later on in 2006 they changed the naming and called them as JSE, JEE and JME.
These editions were named based on the kind of application which can be developed by learning that edition.
Java Standard Edition(JSE):- This is the most basic version of Java and it provides us core concepts of java language like the basic types ,variables, operators and objects as well as high-level classes, arrays, that are used for networking, security, database access, graphical user interface(GUI) development etc.
Since it teaches us core concepts of Java that is why many people call it CORE JAVA, although Sun never gave this name.
It used for developing desktop applications like calculators, chat application, single user game etc.
Java Enterprise Edition(JEE):- The Java EE which stands for Java Enterprise Edition is built on top of the Java SE platform and is a collection of libraries used for building "enterprise applications"(usually web applications).
In simple terms, we can say JEE is used for developing web applications which run on server.
Some popular applications developed using JEE are:- amazon.in, alibaba.com, irctc.co.in, ideacellular.com, airtel.in etc.
However, we can not directly start learning JEE unless we know JSE.
Java Micro Edition(JME):- Java ME is the slimmer version of Java targeted towards small devices such as mobile phones.
Generally people tends to think of the micro edition as the mobile edition. In reality, the micro edition is used not just for mobile phones, but for all kind of devices such as television sets, printers, smart cards and more.
But as Smartphone technology arrived the use of JME has reduced as Android has superseded it.
Components of Java:- When we download Java or JSE, we get 3 major components which are:-
1) JVM:- Java Virtual Machine
2) JRE:- Java Runtime Environment
3) JDK:- Java Development Kit
Java Virtual Machine(JVM):- JVM is an abstract machine that can execute pre-compiled java programs.
In simple terms, it is the code execution component of Java.
It is designed for each platform(OS+CPU) supported by Java and this means that every platform will have a different version of Java.
Why JVM is called a virtual machine?
Ans:- JVM is called virtual machine because it is a software layer but it behaves as if it is a complete machine(platform) that is all the tasks which are done by a machine while running a program in other languages like c c++, are actually done by JVM in Java.
For example:- starting the execution by calling main(), allocating memory for the program, memory cleanup etc.
JVM contains following important components:-
1) Interpreter
2) Garbage Collector
Are Java Compiler and Interpreter same?
Ans:- No, not at all.
The Java compiler converts source code to byte code and it is not a part of JVM, rather it comes with JDK. The interpreter lives inside the JVM and converts byte code to machine understandable form.
Java Runtime Environment(JRE):- JRE is an acronym for Java Run-time Environment.
It contains a JVM along with JVM along with Java classes, packages and set of runtime libraries. So the JVM, while running a Java program uses the classes and other libraries supplied by JRE.
If we do not want to write a Java program, and we just want to run it then we only need a JRE.
Java Development Kit(JDK):- It is a bundle of software that we can use to develop java based applications. It means that it is the complete set, we require for compiling as well as the running the Java program.
It itself contains the JRE, set of library classes, Java compiler, jar(java archives) and additional files needed to write Java applications.
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