Cannot output my result using setText

Question

Everything in my code works fine except for the very last line. I have created a program that calculates a grade based on 5 inputs. After calculating the grade i try and display the result in the output field in my window. The line readsoutput.setText(grade) but it gives me the error when i compile "cannot find symbol". Now if i changed the variable (grade) to a value like ("100") it works no problem, so it appears that the problem has something to do with my variable, which is type double. I cannot figure out how to make my variable display in the output field. The full code is below. Thanks for your help.
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.util.*;
public class gradeCalculator extends JFrame implements ActionListener
public static final int WIDTH = 300;
public static final int HEIGHT = 240;
private TextField inputOne;
private TextField inputTwo;
private TextField inputThree;
private TextField inputFour;
private TextField inputFive;
private TextField output;
public static void main(String[]args)
gradeCalculator Calculator = new gradeCalculator();
Calculator.setVisible(true);
public gradeCalculator()
setTitle("GradeBook Calculator");
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setSize(WIDTH,HEIGHT);
Container contentPane = getContentPane();
contentPane.setLayout(new BorderLayout());
JPanel scorePanel = new JPanel();
scorePanel.setLayout(new GridLayout(5,2));
scorePanel.setBackground(Color.LIGHT_GRAY);
JLabel labelOne = new JLabel("Unit One: ",JLabel.RIGHT);
scorePanel.add(labelOne);
inputOne = new TextField ("",15);
inputOne.setBackground(Color.white);
scorePanel.add(inputOne);
JLabel labelTwo = new JLabel("Unit Two: ",JLabel.RIGHT);
scorePanel.add(labelTwo);
inputTwo = new TextField ("",15);
inputTwo.setBackground(Color.white);
scorePanel.add(inputTwo);
JLabel labelThree = new JLabel("Unit Three: ",JLabel.RIGHT);
scorePanel.add(labelThree);
inputThree = new TextField ("",15);
inputThree.setBackground(Color.white);
scorePanel.add(inputThree);
JLabel labelFour = new JLabel("Unit Four: ",JLabel.RIGHT);
scorePanel.add(labelFour);
inputFour = new TextField ("",15);
inputFour.setBackground(Color.white);
scorePanel.add(inputFour);
JLabel labelFive = new JLabel("Lab: ",JLabel.RIGHT);
scorePanel.add(labelFive);
inputFive = new TextField ("",15);
inputFive.setBackground(Color.white);
scorePanel.add(inputFive);
contentPane.add(scorePanel,BorderLayout.NORTH);
FlowLayout layout = new FlowLayout();
layout.setAlignment(FlowLayout.RIGHT);
JPanel averagePanel = new JPanel();
averagePanel.setLayout(layout);
averagePanel.setBackground(Color.GRAY);
JLabel average = new JLabel("Average: ");
averagePanel.add(average);
output = new TextField("",15);
output.setBackground(Color.white);
averagePanel.add(output);
contentPane.add(averagePanel,BorderLayout.CENTER);
JPanel buttonPanel = new JPanel();
buttonPanel.setLayout(new FlowLayout());
buttonPanel.setBackground(Color.LIGHT_GRAY);
JButton calButton = new JButton("Calculate");
calButton.addActionListener(this);
buttonPanel.add(calButton);
JButton resetButton = new JButton("Reset");
resetButton.addActionListener(this);
buttonPanel.add(resetButton);
contentPane.add(buttonPanel,BorderLayout.SOUTH);
public void actionPerformed(ActionEvent e)
if(e.getActionCommand().equals("Reset"))
inputOne.setText("");
inputTwo.setText("");
inputThree.setText("");
inputFour.setText("");
inputFive.setText("");
output.setText("");
else if(e.getActionCommand().equals("Calculate"))
String expression;
int result;
double grade;
expression = inputOne.getText();
result = Integer.parseInt(expression);
expression = inputTwo.getText();
result += Integer.parseInt(expression);
expression = inputThree.getText();
result += Integer.parseInt(expression);
expression = inputFour.getText();
result += Integer.parseInt(expression);
expression = inputFive.getText();
result += ((Integer.parseInt(expression))*0.5);
grade = (result/4.5);
output.setText(grade);
}

Answer 1

Thanks, I kinda knew what I needed to do, but couldn't quite figure it out. Your info pointed me in the right direction. I changed my code to this
String string = Double.toString(grade);
output.setText(string);and it seems to work fine now.
Thanks for your help.