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Editorial Team
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Asked: 2026-05-16T16:20:18+00:00

Hey, this is probably a simple question, but I am having trouble running my

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Hey, this is probably a simple question, but I am having trouble running my java program from command line. I have 3 java files that I compiled and now I have 3 class files in a directory. I want to run them and pass a string parameter to my main.

Code Sample:

package dfa;
public class Main {

public static void main(String[] args) {

    DFA myDFA = new DFA();

    run(myDFA, args);
}

public static void run(DFA myDFA, String[] args)
{
    String test = args[0];
    if(myDFA.accept(test))
        System.out.println("yes");
    else
        System.out.println("no");
}
}

How I am running it:

java -classpath . Main.class testString

Error:

Exception in thread "main" java.lang.NoClassDefFoundError: Main/class
Caused by: java.lang.ClassNotFoundException:Main.class
.
.
.
.
Could not find the main class: Main.class

New Error:

Exception in thread "main" java.lang.NoClassDefFoundError: dfa/class
Caused by: java.lang.ClassNotFoundException:dfa.class
....Could not find the main class: dfa.Main
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1 Answer

  1. Editorial Team

    You shouldn’t put the .class extension when your run java.

    java -classpath . Main testString is enough if you class is in the default package.

    By default, the first non-option argument is the name of the class to be invoked. A fully-qualified class name should be used.

    It means that if your class is in a package you have to use java my.package.project.Main

    In your case :

    java -classpath . dfa.Main testString

    To execute this command you must be in the parent folder of dfa directory.

    Resources :

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