运行简单的Java程序时出现NOClassDefFound错误

Question

This code is compile fine, but whenever I try to run, it gives an error says NoClassDefFound. What is the possible reason and solution, please explain.

package myPack;

public class PasswordVerification
{
    public boolean verify(String usrId, String pass)
    {
        if(usrId.equals("pranjut")&&pass.equals("password"))
        {
            return true;
        }else
        {
            return false;
        }
    }

    public static void main(String [] main)
    {
         PasswordVerification vp=new PasswordVerification();
         System.out.println(vp.verify("pranjut","password"));
    }

}

Answer 1

Are you sure you're calling with the correct package name prefix (ie "java myPack.PasswordVerification")?

Also, there are some improvements you can make-

• Testing a string variable, better to test the constant against the variable- eg if ("prajnut".equals(userId) rather than if (userId.equals), as the first form is immune to NullPtrExceptions if you happen to pass in an empty string.

• you can simplify by removing the "else" clause -you really only need 1 line

  return "prajnut".equals(id)&& "password".equals(pass):

Answer 2

Make sure you are in the directory that contains the myPack folder. You should not be within the myPack folder. I just tried it on my linux machine and it looks like it automatically included the working folder in the classpath, but only if the CLASSPATH environment variable is NOT set. If it is set, then you should either add the current folder to it, or specify the classpath on the command line as follows:

java -cp . myPack.PasswordVerification

Answer 3

Be sure that you're at the root project.

if you type "dir" ( windows) or "ls" other Unix-like os, you should see a directory name "myPack".

then type java myPack.PasswordVerification

here some suggestion to code better and respect the Java coding conventions

package myPack;

public class PasswordVerification{


    public boolean verify(String usrId, String pass){
        if("pranjut".equals(usrId) && "password".equals(pass)){
            return true;
        }
        return false;

    }

    public static void main(String[] main){
       PasswordVerification vp=new PasswordVerification();
       System.out.println(vp.verify("pranjut","password"));
    }

}