Difference between JDK, JRE and JVM.

Hello viewers, Once again welcome back to Java Jagran. Today I am going to discuss "Difference between JDK, JRE and JVM". So Let's start:

JDK

• JDK is an acronym for Java Development Kit. 
• It physically exists. 
• It contains JRE + development tools. 

JDK is also known as Java Development Kit which provides all necessary tools to develop any Java application as well as run it.

JRE

• JRE is an acronym for Java Runtime Environment. 
• It is used to provide a runtime environment. 
• It is the implementation of JVM. 
• It physically exists. 
• It contains set of libraries + other files that JVM uses at runtime. 
• Implementation of JVMs is also actively released by other companies besides Oracle.

Java Runtime Environment provides all necessary libraries and files which is required by JVM to execute any bytecode/.class file. For example: If you want to run any applet on your browser you have to install JRE on your system.

JVM

• JVM (Java Virtual Machine) is an abstract machine. It is a specification that provides a runtime environment in which java bytecode can be executed.
• JVMs are available for many hardware and software platforms. JVM, JRE and JDK are platform dependent because the configuration of each OS differs. But, Java is platform independent.
• The JVM performs following main tasks:

• Loads code
• Verifies code
• Executes code
• Provides runtime environment

As a developer, we write a Java program i.e *.java file. Further, we compile the Java program and the *.class file is generated which is also known as bytecode. Now to execute this bytecode we need a something. But what exactly is that? Java Virtual Machine(JVM) is a virtual machine which runs the Java bytecode/.class file and generates the output.

Features of Java

Hello Readers, Once again welcome back to Java Jagran. Today I am going to discuss features of java. There is given many features of java. They are also known as java buzzwords. Here I am listing some important features of java.

• Simple
• Object-Oriented
• Platform independent
• Secured
• Robust
• Architecture neutral
• Portable
• Dynamic
• Interpreted
• High Performance
• Multithreaded
• Distributed

Now let's discuss each feature in detail.

Simple:

• The syntax is based on C++ (so easier for programmers to learn it after C++).
• Removed much confusing and/or rarely-used features e.g., explicit pointers, operator overloading etc.
• No need to remove referenced objects because there is Automatic Garbage Collection in java.

Object-oriented

• Object-oriented means we organise our software as a combination of different types of objects that incorporate both data and behaviour.
• Object-oriented programming(OOPs) is a methodology that simplifies software development and maintenance by providing some rules.
• Basic concepts of OOPs: Object,Class,Inheritance,Polymorphism,Abstraction,Encapsulation

Platform Independent

• A platform is the hardware or software environment in which a program runs.
• There are two types of platforms software-based and hardware-based. Java provides a software-based platform.The Java platform differs from most other platforms in the sense that it is a software-based platform that runs on the top of other hardware-based platforms.
• It has two components:
• Runtime Environment
• API(Application Programming Interface)
• Java code can be run on multiple platforms e.g. Windows, Linux, Sun Solaris, Mac/OS etc. Java code is compiled by the compiler and converted into bytecode. This bytecode is a platform-independent code because it can be run on multiple platforms i.e. Write Once and Run Anywhere(WORA).

Secured

• Java is secured because: 
• No explicit pointer: Java Programs run inside virtual machine sandbox
• Classloader: Adds security by separating the package for the classes of the local file system from those that are imported from network sources.
• Bytecode Verifier: Checks the code fragments for illegal code that can violate access right to objects.
• Security Manager: determines what resources a class can access such as reading and writing to the local disksecurities
• These are provided by java language. Some security can also be provided by application developer through SSL, JAAS, Cryptography etc.

Robust

• Robust simply means strong. Java uses strong memory management. There are lack of pointers that avoids security problem. There is automatic garbage collection in java.
• There is exception handling and type checking mechanism in java.

Architecture-neutral

• There is no implementation dependent features e.g. size of primitive types is fixed.
• In C programming, int data type occupies 2 bytes of memory for 32-bit architecture and 4 bytes of memory for 64-bit architecture. But in java, it occupies 4 bytes of memory for both 32 and 64 bit architectures.

Portable

• We may carry the java bytecode to any platform.

High-performance

• Java is faster than traditional interpretation since byte code is “close” to native code still somewhat slower than a compiled language (e.g., C++)

Distributed

• We can create distributed applications in java. RMI and EJB are used for creating distributed applications. We may access files by calling the methods from any machine on the internet.

Multi-threaded

• A thread is like a separate program, executing concurrently. We can write Java programs that deal with many tasks at once by defining multiple threads. The main advantage of multi-threading is that it doesn’t occupy memory for each thread. It shares a common memory area. Threads are important for multi-media, Web applications etc.

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