Thread: problem using a text feild

Hello, i am trying to calculate a value the set into a text feild but I Cant get it to work (the variable last). My code is included below, I just cant understand why it does not work. Look at the bottom or so 20 lines also the problem area attached below whole code.

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;
 
 	class Calculator extends JFrame
 	{
 	JTextField firstnumber, operator, answer, secondnumber;  /*initialises the three text feilds*/
 
 
 	JMenu copyMenu;						       		/*creates the menu*/
 	JMenuItem swap, compare; 		           		/*creates the menu options*/
 	JMenuBar bar;                              		/*creates the menu bar*/
 	JButton calculate;
 
 		private JPanel labelTextPanel(String lab, JTextField txt)
	{
		JPanel pan = new JPanel();
		pan.setLayout(new FlowLayout());
		pan.add(new JLabel(lab));
		pan.add(txt);
		return pan;
	}
 
 	public Calculator()
  	{
 	setTitle("calculator");
	setSize(400, 290);
	setLocation(400, 300);
 
	Container c = getContentPane();		       		/*creates the content pane, adds colour and sets a flow layout*/
	c.setBackground(Color.blue);
	c.setLayout(new FlowLayout());
 
	calculate = new JButton("calculate");
  	c.add(calculate);
 
	firstnumber = new JTextField (20);
	c.add(firstnumber);					      		 /*creates the three text feilds on the content box and set length of 20*/
	JPanel p1 = labelTextPanel("first number", firstnumber);
	c.add(p1);
 
	operator = new JTextField (20);
	c.add(operator);
	JPanel p2 = labelTextPanel("operator", operator); /*calls the private method that creates the labels*/
	c.add(p2);
 
	secondnumber = new JTextField (20);
	c.add(secondnumber);
	JPanel p3 = labelTextPanel("secondnumber", secondnumber);
	c.add(p3);
 
	answer = new JTextField (20);
	c.add(answer);
	JPanel p4 = labelTextPanel("answer", answer);
	c.add(p4);
 
	swap = new JMenuItem("Swap");			   		/*adds the two menu options and gives there names*/
	compare = new JMenuItem("compare");
	copyMenu = new JMenu ("Copy and Compare"); 		/*creates the menu option button on bar and gives a title*/
	copyMenu.add(swap);
	copyMenu.add(compare);					   		/*adds the menu options*/
 
	bar = new JMenuBar();
	bar.add(copyMenu);						   		/*creates the bar and adds the previous menu option to the bar*/
	setJMenuBar(bar);
 
 
 
	swap.addActionListener(
	new ActionListener()
	{
	public void actionPerformed(ActionEvent e)
	{
	String temp1 = firstnumber.getText();			/*swaps the contents of the text boxes*/
	String temp2 = secondnumber.getText();
	firstnumber.setText(temp2);
	secondnumber.setText(temp1);
	}
	});
 
	compare.addActionListener(
	new ActionListener()
	{
	public void actionPerformed(ActionEvent e)
	{
	int first;
	int second;
 
	String temp7 = firstnumber.getText();
	String temp8 = secondnumber.getText();
	first = Integer.parseInt(temp7);
	second = Integer.parseInt(temp8);
 
	if (first < second)
	{
	answer.setText("the first number is less than the second");
	}
	else if (first > second)
	{
	answer.setText("the first number is greater than the second");
	}
	else
	{
	answer.setText("they are equal");
	}
 
	}
	});
 
	calculate.addActionListener(
	new ActionListener()
	{
	public void actionPerformed(ActionEvent e)
	{
	int total;
	int first;
	int second;
 
 
	String temp3 = firstnumber.getText();
	String temp4 = secondnumber.getText();
	String temp5 = operator.getText();
	first = Integer.parseInt(temp3);
	second = Integer.parseInt(temp4);
 
	if (temp5 == "-")
	{
	total = first - second;
	String last = Integer.toString(total);
 
	}
 
	}
	}
	);
 
	setVisible(true);						   		/*makes the whole GUI visible and allows the program to be exited*/
	setDefaultCloseOperation (JFrame.EXIT_ON_CLOSE);
  	}
 
 	}

	calculate.addActionListener(
	new ActionListener()
	{
	public void actionPerformed(ActionEvent e)
	{
	int total;
	int first;
	int second;
 
 
	String temp3 = firstnumber.getText();
	String temp4 = secondnumber.getText();
	String temp5 = operator.getText();
	first = Integer.parseInt(temp3);
	second = Integer.parseInt(temp4);
 
	if (temp5 == "-")
	{
	total = first - second;
	String last = Integer.toString(total);
 
	}
 
	}
	}
	);
 
	setVisible(true);						   		/*makes the whole GUI visible and allows the program to be exited*/
	setDefaultCloseOperation (JFrame.EXIT_ON_CLOSE);
  	}
 
 	}