understand JRE & JDK ,difference between openjdk-8-jdk-headless & openjdk-8-jdk

Question:-1
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what is the difference between JDK & JRE
===============================
JDK stands for java development kit
it provides environment 
to write java code
to compile java code
to execute java code
JDK -YOU CAN WRITE CODE  
     YOU CAN COMPILE CODE
     YOU CAN EXUECTE CODE
JRE
---
JRE stands for Java Run Environment 
it provides execution environment for java application 
JRE -YOU CAN ONLY EXECUTE CODE (TESTING)
     or YOU CAN RUN JAVA CODE (TESTING)  


QA/STAGING/PROD SERVERS:->We recommend JRE only
                         because we run the code only  
DEV SERVERS:------------>We recommend JDK only
                         developer write code
                         compile code
                         execute code 
                         also
                         We recommend JDK 
 
but sometimes we also install JDK in QA/STAGING servers also
to install necessary DEBUG tools which requires JDK
Why we install JDK on QA/Staging Servers
========================================
because JDK includes some of the diagnostic and monitoring tools
sometimes bug appears only the STAGING environment but not in our local machine
in this time these tools will help us..
so, in this context we install JDK also 

Question:-2
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in amazon Linux /redhat Linux servers how to list out a particular package versions?
============================================================
yum whatprovides python
yum whatprovides java 
======================
it list out all the versions of java
EX:OUTPUT 
JAVA 1.8
JAVA 1.11
     1.17
     1.21
     1.25
Question:-3
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in ubuntu servers how to list out a particular package versions
============================================
apt list "python3-*"
apt list "openjdk-*"
====================
it list out all the versions of java
openjdk-8-jdk-headless
openjdk-8-jre-headless
openjdk-8-jdk
openjdk-8-jre
openjdk-11-jdk-headless
openjdk-11-jdk
openjdk-17-jdk-headless
openjdk-17-jdk
openjdk-21-jdk-headless
openjdk-21-jdk
openjdk-21-jre
openjdk-25-jdk-headless
openjdk-25-jdk
openjdk-25-jre-headless

PART-1
======
openjdk-17-jdk-headless ---code -compile - execution -DEV
openjdk-17-jre-headless ---only for execution ---->QA/STAGING/PROD
apt install openjdk-17-jdk-headless
apt install openjdk-17-jre-headless

PART-2
======
openjdk-17-jdk
openjdk-17-jre

Question:-4
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what is the difference between openjdk-8-jdk & openjdk-8-jdk-headless
=====================================================================
generally java software is created for GUI & CLI purpose
but in our case we are using Linux servers /ubuntu server
1.openjdk-8-jdk-headless --->fast install (less files) -less time
it avoids or removes GUI libraires or files from the installation
we get only CLI 
so that it is easy to install jdk fastly in our machine
it is recommended to install 

2.openjdk-8-jdk------------->slow install---(more files) -more time
                             
it installs GUI + CLI completely 
but in our case we are using Linux /ubuntu which is CLI OR CUI 
it is not recommended to install 

Question:-5
-----------
is python available default in ubuntu ?
Yes, Python is available by default on almost every modern version of Ubuntu. 

Question:-6
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is git available default in ubuntu ?
Yes, git is available by default on almost every modern version of Ubuntu.