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You can install OptiFine without also manually installing Java on macOS or Windows. Linux users must manually install Java to play Minecraft, so this guide does not apply. With all of these puzzle pieces in place, your Java JAR file will run without issues.Applies to macOS and Windows Only.

To run JAR files, first make sure you have Java installed, your environment is properly configured, and the JAR file’s manifest file lists the application’s entry-point. JAR files are an excellent way to distribute and deploy cross-platform applications written in Java. When the main-class is not specified in the manifest file, you must use the classpath flag ( -cp), not the -jar flag. Notice the flag to run the JAR file has changed from -jar to -cp. If you know the Java class that should act as the entry point of a runnable JAR, you can explicitly specify that file at the command line as follows: java -cp jarfilename.jar

The JAR file distributor wants you to specify the main-class on the command line.

The main-class to run was not listed in the runnable JAR file’s manifest file.

If you get this error when you run a JAR that should be executable, the problem could be one of these issues: If you try to execute a JAR file that is not meant to be run, you will get an error message that says: Java JAR error: Could not find or load main class. Some are just standard libraries with no execution capabilities at all. You can also open a JAR file in Windows PowerShell or an Ubuntu Terminal window with the following command if you have the JDK installed: jar xf name-of-jar-file.jar Why do I get a ‘Could not load main class’ error when I run my JAR? You can open Java JAR files with any Zip utility such as 7-Zip or WinRAR. If you look inside at its contents, you can open a JAR file and extract its contents with any standard ZIP or decompression utility. How do I extract the contents of a JAR file? A Java JAR file is really just a ZIP file with a.

The Java JAR file uses a standard compression algorithm used by all of the most popular tools. The JAR file encompasses every file required to support an application, zipped up and compressed into a single, archive file. The term ‘archive’ is really key to understanding what a JAR file is. The term JAR is an acronym built from the words: Java Application a Rchive. JAR files are simply ZIP files that contain all of the resources required to run a Java application.

Commands to create, extract and run JAR files Function If the JAR file to run is located in a different folder, you’ll need to provide a full path to the file. This Java JAR run command assumes the JAR in question is located in the current folder. How do you run a JAR at the command line?Īs long as you have Java installed, and the PATH variable points to the \bin directory of the JDK, you issue the following command to run a JAR file at the command line: java -jar jarfilename.jar