Java is a general-purpose programming language that was first released in 1995 by Sun Microsystems (now owned by Oracle Corporation). The language was designed by James Gosling, Patrick Naughton, Chris Warth, Ed Frank, and Mike Sheridan at Sun Microsystems.
JVM stands for Java Virtual Machine. It is a virtual machine that provides an environment for executing Java bytecode. The JVM is responsible for interpreting the bytecode and executing the instructions on the target platform.
The structure of the JVM can be divided into three main components:
1. Classloader:The Classloader is responsible for loading the bytecode of the class files into the JVM. It loads the class files from the file system, network or other sources, and converts them into the internal representation used by the JVM.
2. Runtime Data Area:The Runtime Data Area is where the JVM stores data and runtime information during the execution of a Java program. It is divided into several components:
* Method Area: The Method Area stores class-level data, such as the class definition, method code, and constant pool.
* Heap: The Heap is the runtime memory area where objects are allocated. All Java objects are allocated on the heap.
* Stack: The Stack is where the JVM stores method-level data, such as local variables, method arguments, and method return values.
* PC Registers: The PC Registers hold the address of the currently executing instruction. Each thread has its own set of PC Registers.
* Native Method Stack: The Native Method Stack is used to store data and information for native methods.
3. Execution Engine:The Execution Engine is responsible for executing the bytecode of a Java program. It contains several components:
* Interpreter: The Interpreter reads the bytecode instructions and executes them one by one.
* Just-In-Time (JIT) Compiler: The JIT Compiler compiles frequently executed bytecode into native machine code for faster execution.
* Garbage Collector: The Garbage Collector is responsible for managing memory on the heap. It automatically frees memory that is no longer needed by the program.
Overall, the JVM is a key component of the Java platform. It provides a layer of abstraction between the Java program and the underlying hardware, allowing Java programs to run on any platform that has a JVM installed.
There are several types of Java applications that can be developed using the Java programming language:
1. Standalone applications:These are applications that run on a user's computer as a standalone program. They don't require an internet connection or a web browser to function. Examples of standalone applications include desktop applications like media players, image editors, and games.
2. Web applications:These are applications that run on a web server and can be accessed by users through a web browser. Java web applications are commonly developed using the Java Servlet API and JavaServer Pages (JSP). Examples of Java web applications include e-commerce websites, online banking systems, and social networking sites.
3. Mobile applications:Java can be used to develop mobile applications for Android devices. Android uses a version of Java called Android Java (or simply, Android). Developers can use the Android Studio IDE and the Android SDK to create mobile applications using Java.
4. Enterprise applications:These are large-scale applications that are used by organizations to manage their business processes. Java is widely used for developing enterprise applications because of its scalability, security, and reliability. Enterprise Java applications typically use frameworks such as Spring and Java Enterprise Edition (Java EE).
5. Embedded systems:Java can also be used to develop software for embedded systems such as microcontrollers, sensors, and other small devices. Java Micro Edition (Java ME) is a version of Java that is specifically designed for embedded systems.
Overall, Java is a versatile language that can be used to develop a wide range of applications, from small standalone applications to large enterprise systems.
