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  • Upgrade from version 8 to version 9 was not backward compatible and resulted in a lot of broken packages hence you will see a lot of companies still using Java 8.

  • Java 8 version number is 1.8. This changed with version 9.

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What is a JDK?
  • JDK is a set of development tools which will help us develop, build and run the java application.
  • These tools are present in the bin directory of the jdk attachments/Pasted image 20220915221906.jpg
    jdb is used for debugging java applications and javac is used for compiling java code.
  • JRE (Java Runtime Environment) is used to run the Java applications on any system.

    • JRE and the java command line utility are the only components required to run already built Java applications on a system.
  • Before version 9 of Java JDK and JRE were shipped as separate components.

    • So if you were not developing a Java application and just wanted to run them then you could have only downloaded the JRE.
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  • After version 9 JRE is packed into JDK.
  • JVM
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Building & Packaging

  • JAR stands for Java Archive it helps compress and combine multiple Java class files and its dependencies into a single distributable package.
    • jar cf JarFileName.jar file1 file2 ....
  • Incase of a web application we have static files like html and css. They are packaged in a WAR (Web Archive) file.
  • When jar command is run it automatically generates a manifest file within the package at path META-INF/MANIFEST.MF

    • This file contains information about the files packaged in jar file and any other meta data about the application
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    • One important information present in the meta data is the entry point to the application.
  • Once jar is built it can be run on any platform using java -jar JarFileName.jar

  • Generating documentation for the code: javadoc -d doc

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  • When working with large software it can get really cumbersome to package and generate documentation for the project.

    • This is where build tools like Maven, ANT and gradle are used.
  • ANT example:

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    • If we want to run specific sections of ANT then we can use ant compile jar

NPM (JavaScript)

  • When you install a npm package they are installed inside the node_modules folder in the current directory.
  • A directory by the name of the package is created it contains different files like, LICENSE, package.json and the lib folder contains the code.
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  • The package.json inside the package is the file which contains meta data for the package like its name, version, author, its git repository.
    • This file is useful when you are troubleshooting issues related to dependency.
When we import a package node first looks for the package in the local node_modules directory if the package is not found then it looks in other locations.

We can find the look up order by priority using the following command. attachments/Pasted image 20220915234559.jpg

  • We can install the package globally using: npm -g install <package-name>
  • There are two types of modules:
    • BuiltIn: These are installed automatically when nodejs is installed for the first time.
    • External


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  • Python versions:
    • Python2: 2000 - 2010
    • Python3: 2008 - Till Date.
  • When we install Python PIP gets installed automatically.
  • If we have multiple python versions then we will have different pips.
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So if you don't know to which python pip is pointing just use pip -V
  • When Python is installed it creates the following package structure.
    • A directory is created for each version of Python under the /usr/lib directory.
  • When we install a python package using pip it places it in the site-packages folder in the appropriate python folder.
    • This may not be completely true as they can also be installed in different locations.
  • Packages can also be 32 bit or 64 bit so a separate path is available.
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Finding the location of a particular package

pip show <package-name> attachments/Pasted image 20220916004310.jpg

  • When importing a package python looks at a list of paths to find and import the package.

    • We can list the paths using print(sys.path)
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  • To install a lot of packages we use requirements.txt

    • pip install -r requirements.txt
  • It is a best practice to specify the version of packages in requirements.txt file.
    • If no version is specified then python will install the latest version of the package.
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  • Upgrading a package: pip install <package-name> --upgrade
  • Uninstalling a package: pip uninstall <package-name>
  • Other package managers:

    • Eggs don't need to be unpacked but they are obsolete
    • Wheels are similar to eggs but they need to be unpacked.
  • To install a wheel package we do pip install package.whl

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Last updated: 2022-09-16