How to Execute a Java .class File from the Command Line?

Executing Java .class Files from Command Line

Executing compiled Java classes from the command line requires some additional steps beyond simply typing "java [class-name]". One common reason for encountering errors is forgetting to include the classpath in the command.

To execute the Echo.class file presented in the question, use the following command:

java -cp . Echo "hello"

The "-cp" option specifies the classpath, which in this case is the current directory (".") where the Echo.class file resides.

Alternatively, if the current directory is not part of the classpath, you can manually add it by setting the CLASSPATH environment variable:

SET CLASSPATH=%CLASSPATH;.
java Echo "hello"

Once the classpath is properly configured, you may encounter a "NoSuchMethodError: main" exception. This error indicates that the main method is missing from the Echo.class file. Ensure that the public static void main(String[] args) method is defined in the Echo class.

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