java split source files

I am new to java and I have two classes (class calc and button) that I need to split into separate files and class calc uses class button. they both compile however when I run class A it fails. How can I do this?

This is the code for class calc

package start; 
import javax.swing.*;  
import java.awt.event.*;  
import java.awt.Container;  
import java.awt.Insets;  
import java.awt.Dimension;  
import button.*;

public class calc {
 private button calc_buttons;

 private static void creategui(){
  JFrame window = new JFrame("hello dynamic window");

  buttons.createbuttons();
  buttons.setOpaque(false);
  window.setContentPane(buttons);
  window.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
  window.pack();
  window.setVisible(true);

 }

 static public void main(String[] args){
  creategui();
 }

}

this is the code for class button

package button;

import javax.swing.*;
import java.awt.event.*;
import java.awt.Container;
import java.awt.Insets;
import java.awt.Dimension;

public class button /*extends JPanel implements ActionListener*/{

 protected static JButton button1, button2, button3, button4, button5, button6, button7;
 protected static JButton button8, button9, button_fact, button_exp, button_sqrt, button_abs;
 protected static JButton button_sin, button_cos, button_tan, button_percent, button_rcl;
 protected static JButton button_MC, button_e, button_pi, 开发者_运维知识库button_Mplus, button_Mminus;
 protected static JButton button_C, button_AC, button_MS, button_sign;
 protected static JButton button_plus, button_minus, button_div, button_mult, button_equal;

 static public void calc_button(){


 }

}

when I compile I get no error messages but when I run the calc class I get this

Exception in thread "main" java.lang.NoClassDefFoundError: calc (wrong name: start/calc) at java.lang.ClassLoader.defineClass1(Native Method) at java.lang.ClassLoader.defineClassCond(ClassLoader.java:632) at java.lang.ClassLoader.defineClass(ClassLoader.java:616) at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:141) at java.net.URLClassLoader.defineClass(URLClassLoader.java:283) at java.net.URLClassLoader.access$000(URLClassLoader.java:58) at java.net.URLClassLoader$1.run(URLClassLoader.java:197) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(URLClassLoader.java:190) at java.lang.ClassLoader.loadClass(ClassLoader.java:307) at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301) at java.lang.ClassLoader.loadClass(ClassLoader.java:248)

Go one directory higher (into the directory that contains "start" and "button") and do this:

java start.calc

By the way, it's a convention to let class names start with a capital letter.