Error creating instance of class from same package

Question

When I try to create an instance of a class that is in the same package, my IDE indicates that the constructor can not be found. Can anyone tell me what is wrong? Thanks. Below are the codes for both classes:
package com.practice;
import java.applet.*;
import java.awt.*;
import javax.swing.*;
public class WebProject extends Applet{
     public void init(){
                // The following line is where the IDE indicates there is an error
          UserInterface gui = new UserInterface();
     } // end init()
     public void start(){
     } // end start()
     public void stop(){
     } // end stop()
     public void destroy(){
     } // end destory()
} // end class
package com.practice;
import java.applet.*;
import java.awt.*;
import javax.swing.*;
public class UserInterface extends Applet{
     JPanel menuPanel = new JPanel();
     JPanel contentPanel = new JPanel();
     JPanel savePanel = new JPanel();
     ImageIcon saveIcon = new ImageIcon("workspace/images/toolbarButtongraphics/general/Save24");
     JButton saveButton = new JButton("Save", saveIcon);
     public UserInterface(){
          savePanel.add(saveButton);
          setLayout(new BorderLayout());
          add(menuPanel, BorderLayout.NORTH);
          add(contentPanel, BorderLayout.CENTER);
          add(savePanel, BorderLayout.SOUTH);
} // end UserInterface class

Answer 1

Thanks for the explanation and example. At first, I didn't understand what you were getting at, but after reading "Using Top-Level Containers" and "How to Use Root Panes" java tutorials it made much more sense. Unfortunately, the books I've read up to this point, did not cover those topics at all. The books simply stated that the first step in creating a Swing gui was to extend the JFrame, or JApplet, or etc.
Unfortunately, my original problem persists. I continue to get compile-time errors such as:
TestUserInterface.java:5: cannot find symbol
symbol: class UserInterface
location: class projects.web.TestUserInterface
                      UserInterface ui = new UserInterface(); Anyone know why?
Both the classes are in the same named packaged. Below is my code:
package projects.web;
import java.awt.*;
import javax.swing.*;
public class UserInterface extends JFrame{
     JPanel menuPanel = new JPanel();
     JPanel contentPanel = new JPanel();
     JPanel selectionPanel = new JPanel();
     JButton save = new JButton("Save");
     JButton addFiles = new JButton("Add");
     public UserInterface(){
     super("File Upload");
     setSize(500, 500);
     menuPanel.add(addFiles);
     selectionPanel.add(save);
     setLayout(new BorderLayout());
     add(menuPanel, BorderLayout.NORTH);
     add(contentPanel, BorderLayout.CENTER);
     add(selectionPanel, BorderLayout.SOUTH);
     } // end constructor
} // end UserInterface class
package projects.web;
public class TestUserInterface{
     public static void main(String[] args){
          UserInterface ui = new UserInterface();
} // end TestUserInterface class