#CoreJava/IntroductionOfJava

What is Java?

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• Java is a class-based objected-oriented programming language.
• It was developed by James Gosling at Sun Microsystems_Inc in 1995, after taking it into possession by the Oracle Corporation in 2009.
• It is a general-purpose, high-level programming language that helps programmers and developers to write code once and run it anywhere.
• Java is considered both a compiled and interpreted language and also dynamically programming language.

Why use java? or List the features of Java programming language.

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• Java is a relatively simple and easy-to-use language compared with C/C++ programming language syntax.
• Java is a high- level and dynamically programming language.
• Some features are java supported very well, like
  • Cross Platform Independent
  • Object-Oriented - (java is not fully supported OOPs Concept)
  • Portable
  • Simple
  • Secure
  • Robust
  • Distributed
  • Architecture neutral
  • Multithreading etc.,
    So, we can use for java programming language.

Applications of Java

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• Mobile Applications (Android App Development based on java) Ex: Netfilx, Uber, etc
• Desktop Applications, Ex: Adobe Acrobat Reader
• Web Applications, Ex: Amazon
• Enterprise Applications, Ex: ERP (Enterprise Resource Planning) System, CRM (Customer Relationship Management) System
• Web Server & Application Server, Ex: Apache Tomcat (WS) and WebSphere, WebLogic (AS)

Why is Java not a pure object-oriented language?

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• Java is not 100% objects-oriented because of the existence of primitive data type.
• In Java some OOps Concept doesn't fully support it, especially the Multiple Inheritance Concept.

What is Architecture neutral?

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• Write Once, Run Anywhere: Java programs can run on any processor, regardless of vendor or architecture.
• Bytecode Independence: Java compiles into bytecode, which is platform-independent and allows cross-platform execution.
• Universal Compatibility: Ensures Java applications run on different systems without modification.

CORA OR WORA

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• Compile Once Run Anywhere
• Write Once Run Anywhere

Why java is a dynamic programming language?

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• If any programming language allows memory allocation is done at Run Time then that programming language is called a Dynamic Programming language. Example: Java, Python, etc.,
• Dynamic Language is designed to optimize programmer efficiency, so you can implement functionally with less code.
• If any programming language allows memory allocation is done at Compile Time then that programming language is called a Static Programming language. Example: C, C++, etc.,

How to run Java on your system?

• Download and install the JDK on your system.
• Check if Java is installed correctly by typing java --version or javac --version in the command prompt.
• If Java isn't installed properly, set the system variable for Java.
• Use an IDE like IntelliJ, Eclipse, or VS Code.
• Save your file with a .java extension (e.g., hello.java).
• Write your code using Java syntax.
• Compile the file by typing javac filename.java.
• Run the compiled file using java filename.

How Java works

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Java compilation and execution process:

1. Compile the Java file with javac filename.java to create bytecode (.class file).
2. Run the bytecode with java filename, which sends it to the JVM.
3. The JVM converts the bytecode into machine code and executes the program to produce the output.

Main Function

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• The main function in Java is the entry point of any Java application. It's where the program starts running.
• public: Accessible by any part of the program.
• static: No need to create an object to call it.
• void: It doesn't return any value.
• String[] args: Accepts command-line arguments.

JDK

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• The Java Development Kit (JDK) is used for developing java applications and applets
• It consists of JRE, compiler, debugger and other tools like archiver, document generator, etc.
• It is responsible for compiling, debugging, and executing.
• It is a platform-independent.

JRE

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• Java Runtime Environment is provided by Java to run the java applications.
• The components of JRE includes JVM, Class Loader, Bytecode verifier, Interpreter and Other libraries, etc.
• JVM is the most important component of JRE.
• It is a platform-dependent.

JVM

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• Java Virtual Machine is a part of the JRE.
• It is a specification that provides a run-time environment for Java applications.
• JVM is the responsible for executing bytecode.
• It is converting the byte code to machine code.
• It is a platform-dependent.

Compiler

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• A compiler is a tool which is used to translates the entire source code into intermediate code, known as bytecode, that bytecode, which is stored in a .class file.
• The compiled bytecode is platform-independent.

Compilation Time

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The time taken to convert the entire source code into bytecode.

Execution (or Runtime)

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The process of converting the .class file (bytecode) into binary or machine code and running the program with the given input.

Interpreter

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• Interpreter is used to execute the instructions line-by-line.
• It allows step-by-step execution of the program.

JIT

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• JIT is an integral part of the JVM.
• It is used to translate the bytecode into native machine code.
• This can result in faster performance and better runtime.

Garbage Collector

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• Garbage Collector is used to automatically manage the memory.
• It is used to allocate and deallocate memory.
• The developers don't involve these memory allocation process.

Features of garbage collector

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The features of garbage collection in Java are:

1. Automatic Memory Management: It automatically frees up memory by removing objects that are no longer in use.
2. No Manual Deallocation: Developers don't need to manually release memory, reducing errors.
3. Handles Circular References: It can detect and remove objects that reference each other but are no longer needed.

Allocate and Deallocate Memory

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In Java, memory is managed automatically:

1. Allocate Memory: Use the new keyword to create objects, which allocates memory from the heap.

   • Example: Person p = new Person();

2. Deallocate Memory: Java uses Garbage Collection to automatically free memory for objects that are no longer used, so you don’t need to manually deallocate it.

Byte Code

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• Bytecode in Java is the intermediate code generated after you compile your Java program.
• It's not machine-specific but can be understood by the Java Virtual Machine (JVM), which translates it into machine code for execution.
• Bytecode makes Java platform-independent.

Why java is a secured language?

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• Yes, Java is a secure language because its bytecode is protected, and no one can read it. Only the JVM can read and execute the bytecode.
• The bytecode runs in the JRE (Java Runtime Environment), and it won't work outside the JRE.
• Java's security manager and bytecode verification further enhance its safety.

Java is robust nature, how?

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• Java uses less hardware, making it better for memory management, performance, and efficiency.