Definition for JDK,JRE,JVM,JIT

Source: Dev.to

01. How to download the JDK?

1. Open the command prompt.
2. Run java --version and press Enter.
3. If the JDK is installed, the version will be displayed.
4. If the command is not recognized, download and install the JDK from the official Oracle (or OpenJDK) website.

02. How to write a Java program using Notepad?

• Open Notepad (or Notepad++).
• Write your Java code.
• Save the file with a .java extension (e.g., HelloWorld.java).

03. How to set the command‑prompt path

1. Open the terminal or Command Prompt.

2. Navigate to the folder containing your source file, e.g.:

   cd Desktop

3. If the path is not set correctly, locate the folder in Explorer, copy its full path, and use:

   cd "C:\Path\To\Your\Folder"

4. Once the correct directory is set, you can compile and run the program.

04. How to compile and run the Java program using the command prompt

1. Open the terminal or Command Prompt and change to the directory where the .java file resides.

2. Compile the source file:

   javac HelloWorld.java

3. Run the compiled class:

   java HelloWorld

You should see the program’s output in the console.

05. Software for Java development

• Eclipse IDE
• Visual Studio Code
• IntelliJ IDEA

06. What is the JDK?

• JDK = Java Development Kit
• A software development kit used to write, compile, and run Java programs.
• Converts .java source files into .class bytecode files.

07. What is the JRE?

• JRE = Java Runtime Environment
• Provides the runtime environment (memory, libraries, etc.) required to run compiled Java programs.
• Utilizes the JVM to execute bytecode.

08. What is the JVM?

• JVM = Java Virtual Machine
• Executes Java bytecode on any platform that has a compatible JVM implementation.
• Every time you run a Java program, the JVM loads and runs the bytecode.

09. What is JIT?

• JIT = Just‑In‑Time Compiler
• Compiles parts of the bytecode to native machine code at runtime, improving performance.
• Operates automatically inside the JVM.