How do I execute a Java .class file from the command line?

Executing Java .class Files from the Command Line

When attempting to execute a compiled Java class from the command line, such as Echo.class, users may encounter errors due to incorrect command syntax or classpath issues.

To properly execute Echo.class, use the following command:

java -cp . Echo "hello"

-cp Flag: This flag specifies the classpath, which is where Java searches for .class definitions. Here, the . (current directory) is added to the classpath.

Assuming Proper Compilation:

Ensure that the Echo.class file was compiled using javac Echo.java.

Potential Error: NoSuchMethodError

If after executing the correct command, an error message similar to Exception in thread "main" java.lang.NoSuchMethodError: main appears, it indicates that the Echo class does not have a main method. To fix this, confirm that the class contains the following code:

<code class="java">public class Echo {
    public static void main (String arg) {
        System.out.println(arg);
    }
}</code>

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