How to know the command line used by Eclipse to run the java program?

You can check the other parameters arguments, classpath, environment variables etc. that eclipse might be using to compile your program, from the Run Configurations window, which appears as a dropdown when you click the drop-down button next to the Run button in eclipse.

To get the full command line, you can open the Debug view from Window>Show View>Other.... Right click on the last launch and go to properties. Eclipse will list the exact command line.

The thing is Eclipse uses (by default) different directories for source and object files. If you want to execute a particular java file from the command line, you can either compile it by going inside your workspace directory/src directory and hit javac <MyClass>.java and then do java MyClass.

Or since it works in eclipse, you can go inside the 'bin' directory inside your workspace and do a java MyClass which will execute your pre compiled class.

As of 2019 (version 4.13.0):

Eclipse > Run > Run Configurations

There is a "Show Command Line" button that shows the full command Eclipse uses: