ActionListener needs to Respond to User pressing Enter key

package TemperatureConverter;

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.border.*;
import java.text.*;

public class ConvertTempFrame extends JFrame 
{
	
	/**
	 * 
	 */
	private static final long serialVersionUID = 1L;
	private ActionListener earpiece;
	private JTextField inputbox = new JTextField(10);
	private JTextField outputbox = new JTextField(10);
	private JRadioButton CelsiusIn;
	private JRadioButton FahrenheitIn;
	private JRadioButton KelvinIn;
	private JRadioButton CelsiusOut;
	private JRadioButton FahrenheitOut;
	private JRadioButton KelvinOut;
	private JLabel inputTitle = new JLabel("Temp Value:");
	private JLabel outputTitle = new JLabel("Converted Temp Value:");
	DecimalFormat two = new DecimalFormat("0.00");
	
	public ConvertTempFrame()
		{
		//creates 2 panels for border with the input and the output fields
		JPanel inputPanel = new JPanel();
		inputPanel.add(inputTitle);
		inputPanel.add(inputbox);
		JPanel outputPanel = new JPanel();
		outputPanel.add(outputTitle);
		outputPanel.add(outputbox);
		outputbox.setEditable(false);
		add(inputPanel, BorderLayout.NORTH); 
		add(outputPanel, BorderLayout.SOUTH);
		class ChoiceListener implements ActionListener 
		{
			public void actionPerformed(ActionEvent event) 
			{
				outputConvertedTemp();//performed when a button is selected
			}
		}
		earpiece = new ChoiceListener();
		createConversionTable();
		setSize(400, 200);
	}
	public void createConversionTable()
	{
		//creates center panel to hold radio button panels
		JPanel leftPanel = RadioButtonInput(); 
		JPanel rightPanel = RadioButtonOutput();
		JPanel conversionTable = new JPanel();
		conversionTable.setLayout(new GridLayout(1, 2));
		conversionTable.add(leftPanel);
		conversionTable.add(rightPanel);
		add(conversionTable, BorderLayout.CENTER);
	}
	public JPanel RadioButtonInput()
	{
		//creates the input radio buttons, groups them, aligns them, puts a border on, returns the panel
		CelsiusIn = new JRadioButton("Celsius");
		CelsiusIn.addActionListener(earpiece);
		FahrenheitIn = new JRadioButton("Fahrenheit");
		FahrenheitIn.addActionListener(earpiece);
		KelvinIn = new JRadioButton("Kelvin");
		KelvinIn.addActionListener(earpiece);	
		ButtonGroup group = new ButtonGroup();
		group.add(CelsiusIn);
		group.add(FahrenheitIn);
		group.add(KelvinIn);
		JPanel radioButtonsInput = new JPanel();
		radioButtonsInput.setLayout(new GridLayout(3, 1));
		radioButtonsInput.add(CelsiusIn);
		radioButtonsInput.add(FahrenheitIn);
		radioButtonsInput.add(KelvinIn);
		radioButtonsInput.setBorder(
				new TitledBorder(new EtchedBorder(), "Degree Input"));
		return radioButtonsInput;		
	}
	public JPanel RadioButtonOutput()
	{
		//creates the output radio buttons, groups them, aligns them, puts a border on, returns the panel
		CelsiusOut = new JRadioButton("Celsius");
		CelsiusOut.addActionListener(earpiece);
		FahrenheitOut = new JRadioButton("Fahrenheit");
		FahrenheitOut.addActionListener(earpiece);
		KelvinOut = new JRadioButton("Kelvin");
		KelvinOut.addActionListener(earpiece);
		ButtonGroup group2 = new ButtonGroup();
		group2.add(CelsiusOut);
		group2.add(FahrenheitOut);
		group2.add(KelvinOut);
		JPanel radioButtonsOutput = new JPanel();
		radioButtonsOutput.setLayout(new GridLayout(3, 1));
		radioButtonsOutput.add(CelsiusOut);
		radioButtonsOutput.add(FahrenheitOut);
		radioButtonsOutput.add(KelvinOut);
		radioButtonsOutput.setBorder(
				new TitledBorder(new EtchedBorder(), "Degree Output"));
		return radioButtonsOutput;		
	}
	
	
	public void outputConvertedTemp()
	{
		
		//reads buttons selected to determine output
		int temp;
		double newtemp = 0;
		temp = Integer.parseInt(inputbox.getText());
		if (CelsiusIn.isSelected() & KelvinOut.isSelected())
			newtemp = (temp + 273.15);//c to k
		else if (FahrenheitIn.isSelected() & KelvinOut.isSelected())
			newtemp = ((temp + 459.67) * 0.556);//f to k
		else if (KelvinIn.isSelected() & FahrenheitOut.isSelected())
			newtemp = (((temp * 1.8) - 459.67));//k to f
		else if (CelsiusIn.isSelected() & FahrenheitOut.isSelected())
			newtemp = (((1.8) * temp) + 32);//c to f
		else if (FahrenheitIn.isSelected() & CelsiusOut.isSelected())
			newtemp = ((.556) * (temp - 32));//f to c
		else if (KelvinIn.isSelected() & CelsiusOut.isSelected())
			newtemp = (temp - 273.15);//k to c
		//the following are to ensure that the output stays what it should be
		else if (CelsiusIn.isSelected() & CelsiusOut.isSelected())
			newtemp = temp;
		else if (FahrenheitIn.isSelected() & FahrenheitOut.isSelected())
			newtemp = temp;
		else if (KelvinIn.isSelected() & KelvinOut.isSelected())
			newtemp = temp;
		String degree = "" + (char)186;
		outputbox.setText(" " + two.format(newtemp) + degree);
		
	}	
}

package TemperatureConverter;
import javax.swing.*;
public class ConvertTemp 
{
	public static void main(String[] args) 
	{
		//creates main box panel for everything to go in
		JFrame frame = new ConvertTempFrame();
		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		frame.setTitle("Temperature Converter");
		frame.setVisible(true);
	}
}