The Java ecosystem is the broad set of tools, technologies, libraries, and frameworks that surround and support the Java programming language. It encompasses everything needed to develop, deploy, and manage Java applications. It revolves around JDK, JRE, JVM
The JVM acts like a translator that allows your computer to run Java programs and other languages compiled into Java bytecode. It translates the code into something your computer's hardware can understand and execute.
Loading load
Load .class files into memory. Locates, loads, and links class files (Java bytecode) for execution.
Linking
Initialization
Initialization is the final step where the JVM prepares a class or interface for use. This step happens after the class has been loaded (into memory) and linked.
Method Area
Method area Stores class-level data such as methods and variables, the runtime constant pool, and code for methods.
public class Person {
private String name;
public void setName(String name) {
this.name = name;
}
}
When you define a class Person, the Method Area stores the structure of the Person class, including its methods (setName) and fields (name), and the runtime constant pool which contains references like method names and constant values.
Heap
Heap is where the runtime memory objects are allocated. The heap is shared among all threads and is where the garbage collection process occurs.
Person p = new Person();
When you create a new Person object, it is allocated on the Heap.
Stack Area
Stack area stores frames, which contain local variables, operand stacks, and references to the runtime constant pool of the class being executed. Each thread has its own stack.
public void someMethod() {
int a = 10;
int b = 20;
int sum = a + b;
}
Each time someMethod is called, a new frame is pushed onto the Stack Area. This frame includes local variables (a, b, and sum), an operand stack for intermediate calculations, and a reference to the method’s class in the Runtime Constant Pool.
Program Counter (PC) Register
PC contains the address of the current JVM instruction being executed. Each thread has its own PC register.
Native Method Stack
Similar to the Java stack, but used for native methods.
Interpreter
Interpreter reads Java bytecode and executes it line by line, converting each bytecode instruction into a sequence of machine-level instructions that can be executed by the CPU.
Just-In-Time (JIT) Compiler
Converts bytecode into native machine code at runtime to improve performance.
Garbage Collector
Garbage collector is responsible for automatically managing memory in the JVM. It identifies and deallocates memory that is no longer in use, freeing it up for new objects.
JRE is a software package that provides the necessary environment to run Java applications. It is designed to execute Java bytecode on a machine, making it an essential part of the "write once, run anywhere" (WORA) principle of Java.
public class Person {
private String name;
public void setName(String name) {
this.name = name;
}
}
Person p = new Person();
public void someMethod() {
int a = 10;
int b = 20;
int sum = a + b;
}
JDK (Java Development Kit) │ ├── JRE (Java Runtime Environment) │ │ │ ├── JVM (Java Virtual Machine) │ │ ├── Class Loader │ │ ├── Bytecode Verifier │ │ ├── Execution Engine │ │ │ ├── Interpreter │ │ │ ├── Just-In-Time (JIT) Compiler │ │ │ └── Garbage Collector │ │ └── Runtime Libraries (core libraries like java.lang, java.util, etc.) │ │ │ └── Java APIs (Core libraries and additional libraries) │ ├── Development Tools (like javac, jdb, jar, javadoc, etc.) └── Documentation (API docs, guides)
Exécution<🎝>Tâches
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Classe<🎝>Bibliothèques
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Java<🎝>Native<🎝>Interface<🎝>(JNI)
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Sécurité<🎝>Responsable<🎝>
Le <🎝>Security<🎝>Manager<🎝>applique<🎝>des<🎝>politiques<🎝>de sécurité<🎝>pour les<🎝>Java<🎝>applications,<🎝>restreignant<🎝>les actions<🎝>telles<🎝>que <🎝>l'accès<🎝>aux fichiers, aux<🎝>connexions<🎝>au réseau<🎝>et<🎝>l'<🎝>exécution<🎝>de<🎝>potentiellement<🎝>dangereux<🎝>code.
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javac<🎝>(Java<🎝>Compilateur)
javac<🎝>est<🎝>utilisé<🎝>pour<🎝>pour<🎝>convertir<🎝>Java<🎝>code source<🎝>(.java<🎝>fichiers)<🎝>en<🎝 >bytecode<🎝>(.class<🎝>fichiers).<🎝>Ce<🎝>bytecode<🎝>est<🎝>puis<🎝>exécuté<🎝>par<🎝>le<🎝>Java<🎝>Virtuel <🎝>Machine<🎝>(JVM).
java<🎝>(Java<🎝>Application<🎝>Lanceur)
java<🎝>commande<🎝>lance<🎝>une<🎝>application Java<🎝>.<🎝>Elle<🎝>charge<🎝>les<🎝>classes<🎝>nécessaires,<🎝> interprète<🎝>le<🎝>bytecode,<🎝>et<🎝>démarre<🎝>l'<🎝>application.
jdb<🎝>(Java<🎝>Débogueur)
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jar<🎝>(Java<🎝>Archive<🎝>Outil)
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javadoc<🎝>(Java<🎝>Documentation<🎝>Générateur)
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| Feature/Aspect | JVM | JRE | JDK |
|---|---|---|---|
| Purpose | Executes Java bytecode | Provides the environment to run Java applications | Provides tools to develop, compile, debug, and run Java applications |
| Includes | JVM itself, which includes class loader, bytecode verifier, and execution engine | JVM + Core libraries (like java.lang, java.util, etc.), and other runtime components | JRE + Development tools (like javac, jdb, jar, etc.), documentation |
| Components | - Class Loader - Bytecode Verifier - Execution Engine (Interpreter, JIT) |
- JVM - Core Java libraries - Java Plug-in - Java Web Start |
- JRE - Java Compiler (javac) - JAR Tool (jar) - Debugger (jdb) - Documentation Generator (javadoc) - Other development tools |
| Main Functionality | Executes Java bytecode, enabling platform independence | Provides the minimum requirements to run Java applications | Allows developers to write, compile, and debug Java code |
| Who Uses It? | End-users running Java applications | End-users running Java applications | Java developers writing and compiling Java applications |
| Installation Size | Smallest | Larger than JVM but smaller than JDK | Largest (includes JRE and development tools) |
| Developer Tools | No | No | Yes (includes compiler, debugger, profiler, etc.) |
| Required to Run Java Programs | Yes | Yes | No (but needed to create Java programs) |
| Platform Independence | Provides platform independence by abstracting the underlying hardware | Yes, because it includes the JVM | Yes, it includes everything from JRE |
| Examples of Usage | - Running any Java application (e.g., desktop applications, servers) | - Running Java applications in production or end-user environments | - Writing and compiling Java code - Packaging applications - Debugging |
| Availability | Part of JRE and JDK | Standalone or part of JDK | Standalone package |
JDK (Java Development Kit) │ ├── JRE (Java Runtime Environment) │ │ │ ├── JVM (Java Virtual Machine) │ │ ├── Class Loader │ │ ├── Bytecode Verifier │ │ ├── Execution Engine │ │ │ ├── Interpreter │ │ │ ├── Just-In-Time (JIT) Compiler │ │ │ └── Garbage Collector │ │ └── Runtime Libraries (core libraries like java.lang, java.util, etc.) │ │ │ └── Java APIs (Core libraries and additional libraries) │ ├── Development Tools (like javac, jdb, jar, javadoc, etc.) └── Documentation (API docs, guides)
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