Class, Parent Help

[whitedragon551]

Ok need your help again.

My instructions are to create a class named Book that contains data fields for title and number of pages. Include get and set methods for these fields. Next, create a subclass named TextBook, which contains additional field that holds a grade level for the TextBook and additional methods to get and set the grade level field. Write an application that demonstrates using objects of each class.

Book.java

//Book.java by Tyler 11/10/2012

import java.util.*;

public class Book

{
private int pageNum;
private String title;
Date today = new Date();

	public Book(int pn, String name)
	{
	pageNum = pn;
	title = name;
	}

	//Setter/Getter for pageNum
	public int getpageNum()
	{
	return pageNum;
	}
	
	public void setpageNum(int pn)
	{
	pageNum = pn;
	}
	//Setter/Getter for Title
	public String getTitle()
	{
	return title;
	}
	
	public void setTitle(String name)
	{
	title = name;
	}
	
	public void display()
	{
	System.out.println("Book.java" + "\nby Tyler " + today);
	System.out.println("Book Title: " + title + "\nNumber of Pages: " + pageNum);
	}
}

TextBook.java

//TextBook.java by Tyler 11/10/2012

public class TextBook extends Book
{
private String gradeLevel;

public TextBook(int pageNum, String title, String gl)
	{
	super(pageNum, title);
	gradeLevel = gl;
	}
	
	//Setter/Getter for gradeLevel
	public String getGradeLevel()
	{
	return gradeLevel;
	}
	
	public void setGradeLevel(String g)
	{
	gradeLevel = g;
	}

	public void display()
	{
	super.display();
	System.out.println("Grade Level: " + gradeLevel);
	}

}

DemoBook.java

//DemoBook.java by Tyler 11/10/2012

public class DemoBook
{
	public static void main(String[] args)
	{
	Book oneBook = new Book(250, "Awesome Story");
	TextBook oneTextBook = new TextBook(350, "Awesomer Story", 12);
	
	oneBook.display();
	oneTextBook.display();
	}
}

Everything has compiled fine. However when I try to run DemoBook.java from the Windows cmd prompt I get an error that says:

C:\Users\Tyler\Documents\School Work\CIS280\Project 6>java DemoBook.java
Exception in thread "main" java.lang.NoClassDefFoundError: DemoBook/java
Caused by: java.lang.ClassNotFoundException: DemoBook.java
at java.net.URLClassLoader$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
Could not find the main class: DemoBook.java. Program will exit.

I have no idea what this error means. Ive only seen this when you try to run a program without a main. However this has a main. Not sure whats wrong or where to look.

[whitedragon551]

Fixed it. Changed the setter/getter in TextBook from calling in a String G to String GL and it worked.

[Tolls]

And, presumably, ran it using:
java DemoBook
rather than:
java DemoBook.java
which is incorrect.