Why is Java Platform Independent Language?

Java has established itself as a premier programming language due to its robust features and platform independence. Why is Java Platform Independent? The key lies in its Java Virtual Machine (JVM), which allows Java code to be compiled into bytecode, enabling it to run on any operating system without modification. This “Write Once, Run Anywhere” capability makes Java highly portable compared to languages like C and C++.

Java’s dominance in application development, web development, and tool creation is further strengthened by its object-oriented programming (OOP) principles, including abstraction, encapsulation, inheritance, and polymorphism. Additionally, Java’s extensive library ecosystem and IDE support, such as Eclipse, IntelliJ, and NetBeans, make it a preferred choice for developers.

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What is a Platform, and What is a Platform-Independent Language?

A platform combines hardware and software on which computer programs run. It encompasses the operating system, hardware architecture, and various software components that provide an environment for executing applications. Different platforms can have different hardware architectures, operating systems, and other software configurations. Each platform may have its own set of libraries, APIs, and system resources.

Moreover, if you talk about Platform-Independent Language, it is a programming language that is designed to be executable on different platforms without requiring major modifications to the code. In other words, programs written in a platform-independent language can run on various platforms without significant changes or adaptations.

Java is a prime example of a platform-independent language. It achieves platform independence through the Java Virtual Machine (JVM).

Platform-independent languages like Java offer several advantages. Some of them are: 

• Portability

Programs can be written once and executed on multiple platforms, reducing development effort and maintenance.

• Reduced Compatibility Issues

Since the JVM handles platform-specific details, developers don’t need to worry about low-level platform differences.

• Cost Savings

Developing separate program versions for each platform can be time-consuming and costly. A platform-independent language can reduce these expenses.

• Wider Audience

Platform-independent programs can reach a broader audience as they are not limited to a specific operating system or hardware architecture.

• Consistency

The program’s behavior remains consistent across different platforms, ensuring a predictable user experience.

How does a program execute in Java?

In Java, a program is executed through a series of steps that involve compilation and execution by the Java Virtual Machine (JVM). Here’s a high-level overview of how a Java program is executed:

• Writing the Java Code

You start by writing your Java code using a text editor or an Integrated Development Environment (IDE).

• Compilation

Once you’ve written your Java code, save it with a .java extension. To execute the code, you must compile it into bytecode, a platform-independent intermediate representation. You use the Javac command (Java Compiler) to compile your .java files. Compilation generates .class files containing bytecode.

• Bytecode Generation

During compilation, the Java compiler translates your human-readable source code into bytecode instructions that represent the operations your program should perform.

• Class Loading

The Java Class Loader subsystem loads the compiled .class files. The Class Loader loads the classes into memory when they are first accessed. The class loading process also involves loading referenced classes.

• Bytecode Verification

Before the bytecode is executed, the JVM performs a verification step to ensure that the bytecode is well-formed and doesn’t violate security constraints. This helps prevent runtime errors and security vulnerabilities.

• Execution

The JVM’s execution engine processes the bytecode instructions one by one. It uses Just-In-Time (JIT) compilation techniques to convert some or all of the bytecode into native machine code for the specific platform on which the program is running. This improves execution speed.

• Runtime

While the program runs, the JVM manages memory, thread execution, and other runtime aspects. It also provides various runtime services like garbage collection for memory management.

• Execution Completion or Termination

The program continues to execute until it reaches the main method’s end or an explicit termination condition is met. Once the program’s execution completes, the JVM performs any necessary cleanup operations and terminates.

It’s important to note that why java is platform independent is achieved through the JVM. You write your code once and compile it into bytecode, which can be executed on any platform with a compatible JVM implementation.

Overall, the combination of compilation and execution stages within the JVM allows Java programs to be efficient, secure, and portable across different platforms.

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Compiling a Code

Whenever we write a code, we follow the syntaxes of a programming language, which would have a fair amount of readability. And it contains few words, phrases, variable names, method names, etc. All these things are considered to be human-readable and human-understandable text. Join our fullstack development bootcamp course if you are interested in fullstack. 

So a machine uses a compiler to convert the source code into a machine-readable code which is also referred to as machine-level language. The compiler builds the machine-level code in a specific presentation such that it can be easily understood by the CPU and hence execute it seamlessly. 

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This building of machine-level language differs by each programming language and each operating system. For example, c/c++ generates a .exe file that is not the same for two machines if they are running on a different operating system.

And here arises the problem!

This building of machine-level language differs by each programming language and each operating system. For example, c/c++ generates a .exe file that is not the same for two machines if they are running on a different operating system.

And here arises the problem!

When a machine level language differs by each operating system, then we cannot run a code that is compiled in a different machine in a new machine, unless both of the systems operate on the same operating system. This feels like crap for many programmers and developers.

But Java makes things easier, and java has a solution for this. Let’s get started.

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Why Java is Platform Independent Language?

So what happens when we compile code in java?

Whenever we enter a statement “javac filename.java” or compile a code in java, javac compiles the code. And it creates an intermediate code called Byte Code.

Bytecode adds this important feature in Java of being independent/ portable as this bytecode is independent of the platforms. This dependency eases the tasks as it can be used in various environments with lesser planning and translation.

This is where java makes difference between all different programming languages. It creates a .class file, which is considered as byte code. Whereas languages like c/c++ will create a natively executable code when they are compiled and thus makes them platform dependent.

Hold on, this is too early for celebration. This byte code is not executable. We need a translator for executing this byte code. And JVM does this job. Generally, JVM resides in the main memory of our computer. Java Virtual Machine acts as an interpreter and then executes the byte code generated by javac.

And now we are done, our code gets executed successfully.

So how does java going to manage it all alone?

And the answer would be, it’s because of the JVM. The byte code generated by source code compilation would run in any operating system, but the JVM present in a machine differs for each operating system. And this is how java is considered a platform-independent programming language.

To understand it properly, let’s understand the architecture and working of the JVM.

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JVM Architecture

JVM is part of the java runtime environment and is responsible for converting a .java file into a .class file. When we compile a java code JVM calls the main method in the source code.

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ClassLoader

It is a subsystem in the java virtual machine. It loads the .class file, checks if there are any exceptions and it is the reason for few runtime exceptions. And after checking it allocates the memory for the variables and the methods present, assign default values to variables and arrays. It also executes the static methods or variables present in the code.

The classes are loaded on demand and the java run time is not necessarily supposed to know of the file and its systems as the work is supposed to be done by the classloader.

There are 3 built-in class loaders inJVMm, bootstrap classloader, Extension classloader, Application classloader.

Just to briefly mention the workings of these classes-

1. Bootstrap Classloader- Loads the libraries of Java.
2. Extension Classloader- Load the codes in the directories of extensions or any other directory commanded by the system property.
3. Application Classloader- Loads code found on java.class.path eventually mapping these java.class.path to CLASSPATH environment variable.

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Memory Areas in JVM

Method/Class Area

It stores information like class names, method names, variables. It is a shared resource for all the methods and variables in a class. It works as a memory that stores information important to execute the task. It is shared on all the virtual machine threads. Its size depends upon the computation either fixed or expandable.

Heap

It stores the information of all the data stored in the heap area. It stores the data in a certain amount which will not be known until the program runs. It is used throughout the application. It is used for dynamic memory allocation. The creation of new objects happens in the heap area.

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JVM Language Stack

It stores the information in blocks also called stack-frames/frames, which stores the current information when there is a function call, stores local variables, it also plays a dominant role in thread management.

PC Register

It stores the address of the instruction which is currently being executed. It is useful in a multi-thread execution situation.

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Native Method Stack

It stores all the information of about the native methods used. It can access system-specific functions not available directly in Java. The main objective of this is to improve the system performance by memory-level communication.

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Execution Engine

The Execution engine will execute the byte code, and it removes the allocated memory to the objects which are unreachable or unreferenced. The interpreter in the execution engine will execute the byte code by reading it in a stream and interpreting line by line.

It also has an exciting part called JIT compiler (Just In Time Compiler), where it creates a native executable code for methods, so if there are multiple function calls then the JVM need not interpret it again, rather directly use the native executable code. Hence it improves the performance of execution.

Native Method Interface

This interface is used by java for interacting with the applications implemented in different languages like C/C++. The interaction is bidirectional, where the JVM may call those applications or can be called by those applications. It limits the portability due to the system-specific application of code. It facilitates interaction between native code (written in C/ C++) with other codes ( written in Java or other programming languages). This is also what makes Java platform independent. 

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Native Method Libraries

It keeps track of the native language libraries, which may be used by the execution engine. They are classified as the compilation of codes written for a specific architecture. They are platform-specific files.

Now that we’ve understood the architecture of the JVM let’s get back to our discussion. So this JVM is different for different operating systems, but the output generated by those JVMs will be the same for the same byte code provided.

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Conclusion

In this article we have discussed why is java platform independent. We’ve gone through a few unique features of java, understood what happens when we compile code in languages like C/C++ and understood the difference between natively executable code and byte code. We’ve walked through the explanation of why java is considered a platform-independent language and understood that JVM is the reason behind java’s platform independence. We had a look at JVM architecture for a better understanding. This article must have cleared the understanding if java is platform dependent or independent. 

Now that you are aware of the reason why java is platform-independent, explore other unique features of java and start utilizing them!

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