I'm new to Java and busy working through the Sams - Teach yourself java in 24 Hours.

As I go through all of the workshops I try to understand everthing but I just can't understand the following statement in the LottoMadness Class:

LottoEvent lotto = new LottoEvent(this); - what is "this" refering to?



I also don't understand the constructor method of the LottoEvent class

public LottoEvent(LottoMadness in) {
gui = in;
}




The full code for the LottoMadness and LottoEvent class follows:





import java.awt.*;
import javax.swing.*;

public class LottoMadness extends JFrame {

LottoEvent lotto = new LottoEvent(this);

// set up row 1 ================================================== ==========
JPanel row1 = new JPanel();
ButtonGroup option = new ButtonGroup();
JCheckBox quickpick = new JCheckBox("Quick Pick", false);
JCheckBox personal = new JCheckBox("Personal", true);


// set up row 2 ================================================== ==========
JPanel row2 = new JPanel();
JLabel numbersLabel = new JLabel("Your picks: ", JLabel.RIGHT);
JTextField[] numbers = new JTextField[6];
JLabel winnersLabel = new JLabel("Winners: ", JLabel.RIGHT);
JTextField[] winners = new JTextField[6];

// set up row 3 ================================================== ==========
JPanel row3 = new JPanel();
JButton stop = new JButton("Stop");
JButton play = new JButton("Play");
JButton reset = new JButton("Reset");

// set up row 4 ================================================== ==========
JPanel row4 = new JPanel();
JLabel got3Label = new JLabel("3 of 6: ", JLabel.RIGHT);
JTextField got3 = new JTextField("0");
JLabel got4Label = new JLabel("4 of 6: ", JLabel.RIGHT);
JTextField got4 = new JTextField("0");
JLabel got5Label = new JLabel("5 of 6: ", JLabel.RIGHT);
JTextField got5 = new JTextField("0");
JLabel got6Label = new JLabel("6 of 6: ", JLabel.RIGHT);
JTextField got6 = new JTextField("0", 10);
JLabel drawingsLabel = new JLabel("Drawings: ", JLabel.RIGHT);
JTextField drawings = new JTextField("0");
JLabel yearsLabel = new JLabel("Years: ", JLabel.RIGHT);
JTextField years = new JTextField();

public LottoMadness() {
super("Lotto Madness");
setSize(550, 270);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
GridLayout layout = new GridLayout(5, 1, 10, 10);
setLayout(layout);

// Add listeners ================================================== =====
quickpick.addItemListener(lotto);
personal.addItemListener(lotto);
stop.addActionListener(lotto);
play.addActionListener(lotto);
reset.addActionListener(lotto);


//Create row 1 ================================================== =======
FlowLayout layout1 = new FlowLayout(FlowLayout.CENTER,
10, 10);
option.add(quickpick);
option.add(personal);
row1.setLayout(layout1);
row1.add(quickpick);
row1.add(personal);
add(row1);



//Create row 2 ================================================== =======
GridLayout layout2 = new GridLayout(2, 7, 10, 10);
row2.setLayout(layout2);
row2.add(numbersLabel);
for (int i = 0; i < 6; i++) {
numbers[i] = new JTextField();
row2.add(numbers[i]);
}
row2.add(winnersLabel);
for (int i = 0; i < 6; i++) {
winners[i] = new JTextField();
winners[i].setEditable(false);
row2.add(winners[i]);
}
add(row2);


//Create row 3 ================================================== =======
FlowLayout layout3 = new FlowLayout(FlowLayout.CENTER,
10, 10);
row3.setLayout(layout3);
stop.setEnabled(false);
row3.add(stop);
row3.add(play);
row3.add(reset);
add(row3);


//Create row 4 ================================================== =======
GridLayout layout4 = new GridLayout(2, 3, 20, 10);
row4.setLayout(layout4);
row4.add(got3Label);
got3.setEditable(false);
row4.add(got3);
row4.add(got4Label);
got4.setEditable(false);
row4.add(got4);
row4.add(got5Label);
got5.setEditable(false);
row4.add(got5);
row4.add(got6Label);
got6.setEditable(false);
row4.add(got6);
row4.add(drawingsLabel);
drawings.setEditable(false);
row4.add(drawings);
row4.add(yearsLabel);
years.setEditable(false);
row4.add(years);
add(row4);

setVisible(true);
}

public static void main(String[] arguments) {
LottoMadness frame = new LottoMadness();
}






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

public class LottoEvent implements ItemListener, ActionListener,
Runnable {

LottoMadness gui;
Thread playing;

public LottoEvent(LottoMadness in) {
gui = in;
}

public void actionPerformed(ActionEvent event) {
String command = event.getActionCommand();
if (command.equals("Play")) {
startPlaying();
}
if (command.equals("Stop")) {
stopPlaying();
}
if (command.equals("Reset")) {
clearAllFields();
}
}

void startPlaying() {
playing = new Thread(this);
playing.start();
gui.play.setEnabled(false);
gui.stop.setEnabled(true);
gui.reset.setEnabled(false);
gui.quickpick.setEnabled(false);
gui.personal.setEnabled(false);
}

void stopPlaying() {
gui.stop.setEnabled(false);
gui.play.setEnabled(true);
gui.reset.setEnabled(true);
gui.quickpick.setEnabled(true);
gui.personal.setEnabled(true);
playing = null;
}

void clearAllFields() {
for (int i = 0; i < 6; i++) {
gui.numbers[i].setText(null);
gui.winners[i].setText(null);
}
gui.got3.setText("0");
gui.got4.setText("0");
gui.got5.setText("0");
gui.got6.setText("0");
gui.drawings.setText("0");
gui.years.setText("0");
}

public void itemStateChanged(ItemEvent event) {
Object item = event.getItem();
if (item == gui.quickpick) {
for (int i = 0; i < 6; i++) {
int pick;
do {
pick = (int) Math.floor(Math.random() * 50 + 1);
} while (numberGone(pick, gui.numbers, i));
gui.numbers[i].setText("" + pick);
}
} else {
for (int i = 0; i < 6; i++) {
gui.numbers[i].setText(null);
}
}
}

void addOneToField(JTextField field) {
int num = Integer.parseInt("0" + field.getText());
num++;
field.setText("" + num);
}

boolean numberGone(int num, JTextField[] pastNums, int count) {
for (int i = 0; i < count; i++) {
if (Integer.parseInt(pastNums[i].getText()) == num) {
return true;
}
}
return false;
}

boolean matchedOne(JTextField win, JTextField[] allPicks) {
for (int i = 0; i < 6; i++) {
String winText = win.getText();
if ( winText.equals( allPicks[i].getText() ) ) {
return true;
}
}
return false;
}

public void run() {
Thread thisThread = Thread.currentThread();
while (playing == thisThread) {
addOneToField(gui.drawings);
int draw = Integer.parseInt(gui.drawings.getText());
float numYears = (float)draw / 104;
gui.years.setText("" + numYears);

int matches = 0;
for (int i = 0; i < 6; i++) {
int ball;
do {
ball = (int) Math.floor(Math.random() * 50 + 1);
} while (numberGone(ball, gui.winners, i));
gui.winners[i].setText("" + ball);
if (matchedOne(gui.winners[i], gui.numbers)) {
matches++;
}
}
switch (matches) {
case 3:
addOneToField(gui.got3);
break;
case 4:
addOneToField(gui.got4);
break;
case 5:
addOneToField(gui.got5);
break;
case 6:
addOneToField(gui.got6);
gui.stop.setEnabled(false);
gui.play.setEnabled(true);
playing = null;
}
try {
Thread.sleep(100);
} catch (InterruptedException e) {
// do nothing
}
}
}