If you’re a Java developer, then you may know this aspect of the Java programming language. However, if you’re new to the world of Java or want to learn about Java Virtual Machine, then the information mentioned here will guide you better.
In this blog, we will discuss everything about Java Virtual Machine (JVM) based on the following key points.
Table of Contents
- What is Java Virtual Machine?
- What is the Use of Java Virtual Machine?
- What are the Different Ways of Java Virtual Machine?
- Architecture of Java Virtual Machine
- How Does Java Virtual Machine Work?
- How Does Execution Engine Manage System Resources?
- Memory and Garbage Collection
- Why JVM is Needed?
Let’s get started.
What is Java Virtual Machine?
Any source code needs to be compiled and interpreted before its execution. Java uses the combination of both compiler and interpreter. Java code is first compiled into Java Byte Code which is in Binary form, and then a special Java interpreter interprets them for a particular platform.
Java ByteCode is the machine language for Java Virtual Machine. The JVM translates the compiled binary byte code into a specific machine language. JVM is a subpart of the Java Runtime Environment (JRE).
As the JVM is an abstract machine, it works on top of the current processes. It can be implemented in hardware or software. JVM and Java APIs together make the Java platform. The important use of the JVM is HotSpot.
What is the Use of Java Virtual Machine?
From the above explanation of Java Virtual Machine (JVM), it is clear to say the fact that, it loads, verifies, and executes Java bytecode in the shortest possible time. Best known as the interpreter or the core of Java programming language because it executes Java programming.
What are the Different Ways of Java Virtual Machine?
Java Virtual Machine (JVM) is defined in three different ways as follows:
- The JVM Specification
The JVM is a software specification where its working is specified. However, the execution provider is completely authorized to choose the algorithms.
- The JVM Implementation
The right execution of the SPECIFICATIONS results in an actual software that is called JVM implementation, known as JRE (Java Runtime Environment). There are so many implementations of both open source and proprietary.
- The JVM Instance
Once JVM Specification is implemented correctly and published as a software product, it can be downloaded and run as a program. This downloaded program is the JVM instance.
The Architecture of Java Virtual Machine
Hope the above explanation answered the question – What is Java Virtual Machine? Now, let’s understand the architecture of Java Virtual Machine. The JVM architecture consists of a classloader, memory area, execution engine, and more.
- ClassLoader
The class loader helps in loading class files. It performs three functions – Loading, Linking, and Initialization.
- Method Area
Java Virtual Machine method area stores class structures such as metadata, the regular runtime pool, and the code for methods.
- Heap
Heap stores all the objects, their related instance variables, and arrays. This is because memory is common and shared over multiple threads.
JVM language Stacks
JVM language stacks store local variables, and it is partial outcomes. Each thread comes with its own JVM stack, created concurrently as the thread is created. When a method is invoked, a new frame is created and deleted when the method invocation process is complete.
- PC Registers
The PC register has the address of the JVM instruction which is currently executing, In Java, there is a separate PC register for each thread.
- Native Method Stacks
Native method stacks store the instruction of native code that depends on the native library. It is coded in other languages instead of Java.
- Execution Engine
This software is used to test hardware, software, or entire systems. The test execution engine does not store any data about the tested product.
- Native Method interface
It is a programming framework that allows Java programs that are running in a Java Virtual Machine to call by libraries and native applications.
- Native Method Libraries
Native Libraries is a group of Native Libraries (C, C++) that are required by the Execution Engine.
How Does Java Virtual Machine Work?
Java Virtual Machine acts as a run-time engine to run Java applications. Java calls the main method available in Java code.
JVM is a part of the Java Runtime Environment (JRE).
Java applications are based on the concept of Write Once Run Anywhere (WORA). So, you need to write the Java programs only once and can run the programs on multiple platforms without modifying the Java code.
When a .java file is compiled, the compiler creates the .class files (containing byte-code) with the same names as that of the class available in a .java file.
When a .class file is run, it undergoes various steps.
How Does Execution Engine Manage System Resources?
The Java Virtual Machine disposes the unused memory and, this garbage collection is the mechanism, which actually does that disposal. It also allocates and maintains the referential structure that is taken for granted by the Java developers. Apart from the memory, this execution engine is responsible for managing the resources for file system access and the network I/O. This machine is interoperable across operating systems. For every application’s requirement, the implementation, the engine should be responsive to every Operating system’s environment. This is how the JVM becomes capable of handling all in-the-wild demands.
Memory and Garbage Collection
One of the most common interactions with Java Virtual Machine is all about, “heap and stack”. It displays the memory usage and adjusts the JVM’s memory settings.
In JVM, the memory is managed through a garbage collection feature which is a contrasting method used in other programming languages. However, earlier program memory was a daunting task that was left only for developers to handle.
The garbage Collection feature of JVM always keeps an eye on the program to identify the empty space and remove unused memory to increase performance. The garbage collection is handled inside the JVM instead of the program. Moreover, the process uses the developer’s and operator’s specifications for individual program use.
Why JVM is Needed?
Java Virtual Machine is needed to manage the tasks that it performs and which are crucial for the development of Java programs. JVM performs the following tasks
- Loads the code
- Runs the code
- Validates code
- Provides a reliable run-time environment for different applications
- Offers a memory area
- Provides a Register set
- Provides the garbage collection heap
- Reports critical errors
- Provides a class file format
To Conclude
However, the JVM (Java Virtual Machine) was primarily developed for only JAVA but now, it allows several other scripting and programming languages including Kotlin, Groovy, and Scala. Also, other programming languages like Python with Jython, Common Lisp with Armed Bear Common Lisp, Ruby with JRuby, and JavaScript with Rhino can also run on top of it. Looking forward, it can be said that there is a bright future for JVM and we can see it as a prominent part of the development landscape for sure.
FAQs
Q.1. What does Java Virtual Machine do?
Ans. The Java Virtual Machine performs several operations including Loading code, Verifying code, Executing code, and Providing Runtime Environment. However, it has two primary functions:
- Allowing Java programs to run on any device or OS
- Managing and Optimizing Program Memory
Q.2. Is JVM a software?
Ans. Java Virtual Machine is the specification for a software program that runs code and provides the runtime environment for that code.
Q.3. How many JVMs can run on a single machine?
Ans. Unlimited! You can run multiple JVMs on a single machine. For example, you can run a separate JVM for running applets and another JVM for the execution of Java Byte Code on a single machine.
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