Compiling Jars

To compile Java files into a JAR file, follow these steps:

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1. Compile Java Files into .class Files

Run this in the terminal (assuming your Java files are in the src directory):

javac -d out src/*.java

• -d out places compiled .class files into the out directory.
• src/*.java compiles all Java files in src.

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2. Create a Manifest File (Optional, for Executable JARs)

Create a manifest.txt file specifying the entry point (if applicable):

Main-Class: com.example.Main

(Replace com.example.Main with your actual main class.)

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3. Package Everything into a JAR

Run the following command:

jar cfm app.jar manifest.txt -C out .

• c → Create a JAR.
• f → Specifies the output file (app.jar).
• m → Uses the manifest.txt file.
• -C out . → Adds compiled files from the out directory.

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4. Run the JAR File

If it's an executable JAR:

    java -jar app.jar

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Alternative: Without Manifest

If you don’t need an executable JAR (e.g., it's a library):

jar cf app.jar -C out .

This just creates a JAR of compiled classes without an entry point.

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Automation Using Gradle or Maven

If you're using Gradle, add this to build.gradle:

jar {
    manifest {
        attributes 'Main-Class': 'com.example.Main'
    }
}

Then build it with:

gradle jar

If you're using Maven, package with:

mvn package

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That’s it! 🚀 Now you have a .jar file ready to use.