Exception in thread “main” java.lang.NoClassDefFou

问题:

My file directory:

project/src/m2mcom/entities/AutomatedTelnetClient.java
           /web/Simple.java           
           /org/apache/commons/net/telnet/TelnetClient.java 

The source code of the Simple.java:

package m2mcom.web;
import m2mcom.entities.AutomatedTelnetClient;
import java.util.*;
import java.io.*;

public class Simple {
    public static void main(String [] args) {
        try {
            AutomatedTelnetClient telnet = new AutomatedTelnetClient();
            String answer = telnet.request();
            System.out.println(answer);
        } catch (Exception e) {
            System.err.println("Error");
        }
    }
}

And when I execute Simple.class, without any errors of compilation, I get this error message:

C:\Users\Victor\Desktop\project2\src\m2mcom\web>java Simple
Exception in thread "main" java.lang.NoClassDefFoundError: Simple (wrong name: m
2mcom/web/Simple)

Does anyone know how to solve this?

回答1:

You're executing the command in the wrong folder, with the wrong classname. You need to use the fully qualified name (FQN) when running a Java class. And of course, you have to be in the right directory. In your example, the FQN of your class is m2mcom.web.Simple (combination of the package m2mcom.web and the simple name Simple).

As far as deducing the right directory, your classes are stored in a hierarchical folder structure, which basically starts in C:\Users\Victor\Desktop\project2\src.

So to correctly execute your program, from C:\Users\Victor\Desktop\project2\src, do;

java m2mcom.web.Simple

回答2:

package m2mcom.web;

remove above line and recompile it. when you run your code in netbeans it including in a m2mcom.web package.that is not in your class file.

回答3:

So you have to be in the directory right above the package name when you execute the java command which should be in the form packagename.classname without the .class suffix.