If statement?

I am trying to write a code that converts SAE to metric. I have to have Volume, Weight, and Lenght. under each one of those I need the option of gallon, quart, pint,cup under Volume. Under Weight Pound and ounce and under Length mile, yard, foot and inch.

currently I have a total of 4 classes. I have a Volume class, a Weight Class and a Length class that will accept the number inputed and do the conversion and send it to the main class.

I am trying to do it as an applet I start with the first 3 buttons when a choice is made those buttone are removed and the next set of buttons are redrawn. My problem is when the next choice is made it goes nowhere. I have the different options set up as methods and I am calling the methods.

This is the code I have so far for the main class. if I remove                          if(source == gallonButton)
       gallon();
it will compile but I don't know how to get to the next step. I know it should be simple I am just not getting it.


import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.applet.*;
import java.lang.*;

public class MetricProject12 extends JApplet implements ActionListener
{
      JButton volumeButton = new JButton("Volume");
      JButton lenghtButton = new JButton("Lenght");
      JButton weightButton = new JButton("Weight");
      
      JButton gallonButton = new JButton();
      JButton quartButton = new JButton();
      JButton pintButton = new JButton();
      JButton cupButton = new JButton();
      
      JButton poundButton = new JButton();
      JButton ounceButton = new JButton();
      
      JButton mileButton = new JButton();
      JButton yardButtton = new JButton();
      
      FlowLayout flow = new FlowLayout();
      Container con = getContentPane();
      
            JLabel mainLabel = new JLabel("Metric Conversion Project");
      JLabel optionExplainLabel = new JLabel("Please choose converstion type desired");


      
            public void init()
            {
            con.setLayout(flow);
            
            con.add(volumeButton);
            con.add(lenghtButton);
            con.add(weightButton);
            
            volumeButton.addActionListener(this);
            lenghtButton.addActionListener(this);
            weightButton.addActionListener(this);
            }//end init
            
            public void volume()
            {
                  remove (volumeButton);
                  remove (lenghtButton);
                  remove (weightButton);
                  repaint();
                  
                  FlowLayout flow = new FlowLayout(FlowLayout.CENTER);
                  con.setLayout(flow);
                  
                  JButton gallonButton = new JButton();
                  JButton quartButton = new JButton();
                  JButton pintButton = new JButton();
                  JButton cupButton = new JButton();
                                    
                  con.add(gallonButton);
                  con.add(quartButton);
                  con.add(pintButton);
                  con.add(cupButton);
                  
                  gallonButton.addActionListener(this);
                  quartButton.addActionListener(this);
                  pintButton.addActionListener(this);
                  cupButton.addActionListener(this);
                  
                  gallonButton.setText("Gallon");
                  quartButton.setText("Quart");
                  pintButton.setText("Pint");
                  cupButton.setText("Cup");
                  
            }//end volume
            
            public void weight()
            {
                  remove (volumeButton);
                  remove (lenghtButton);
                  remove (weightButton);
                  repaint();
                  
                  FlowLayout flow = new FlowLayout(FlowLayout.CENTER);
                  con.setLayout(flow);
                  
                  JButton poundButton = new JButton();
                  JButton ounceButton = new JButton();
                                    
                  con.add(poundButton);
                  con.add(ounceButton);
                  
                  poundButton.addActionListener(this);
                  ounceButton.addActionListener(this);
                  
                  poundButton.setText("Pound");
                  ounceButton.setText("Ounce");
                  


            }//end weight
            
            public void length()
            {
                  remove (volumeButton);
                  remove (lenghtButton);
                  remove (weightButton);
                  repaint();
                  
                  FlowLayout flow3 = new FlowLayout(FlowLayout.CENTER);
                  con.setLayout(flow3);

                  JButton mileButton = new JButton("Mile");
                  JButton yardButtton = new JButton("Yard");
                  JButton footButton = new JButton("Foot");
                  JButton inchButton = new JButton("inch");

                  con.add(mileButton);
                  con.add(yardButtton);
                  con.add(footButton);
                  con.add(inchButton);
            
                  mileButton.addActionListener(this);
                  yardButtton.addActionListener(this);
                  footButton.addActionListener(this);
                  inchButton.addActionListener(this);
                  
                  mileButton.setText("Mile");
                  yardButtton.setText("Yard");
                  footButton.setText("Foot");
                  inchButton.setText("Inch");
                  

            }//end lenght()
            
            public void gallon()
            {
                  remove (volumeButton);
                  remove (lenghtButton);
                  remove (weightButton);
                  repaint();
                  

                  String sGallon = JOptionPane.showInputDialog(null,"Please enter the number to be converted:");
                  double gallon = Double.parseDouble(sGallon);
                  
                  Volume vol = new Volume();
                  //creat an object from the Volume class
                  
                  vol.getGallon(gallon);
                  //pass the variable gallon to the getGallon method in the Volume class
                  
                  double liters;
                  liters = vol.getConvertGallon();

                  JLabel outputLabel = new JLabel();
                  outputLabel.setText(sGallon + "Gallons converted into liters is " + liters);
                  
            }//end gallon()
            
      public void actionPerformed(ActionEvent e)
      {
            Object source = e.getSource();
            {
                        if(source== volumeButton)
                        
                        volume();
                         if(source == gallonButton)
                         gallon();
                        
                        else if(source == weightButton)
                        
                              weight();
                        
                        else if(source == lenghtButton)
                        
                              length();
                        
            }//end object source
      }//end action performed
}//end class