1. Drawing in a frame – Java GUI
Lesson 31:
Drawing in a frame – Java GUI

2. The Calculator In this example we will start using
RECAP
In this example we will start using
JLabels
the GridLayout
Typecasting to double from a text input
With use of JButtons, JFrame, Containers, Listeners and JTextFields we will create a calculator java application using the GUI components in the swing library

3. RECAP // MiniCalc.java - demo gridlayout import java.awt.*;
import javax.swing.*;
class MiniCalc{
public static void main (String[] args){
JFrame frame = new JFrame("MiniCalc");
Container pane = frame.getContentPane();
//Creating the major components
JTextField firstNumber= new JTextField(20);
JTextField secondNumber= new JTextField(20);
JTextField result= new JTextField(20);
JButton addButton = new JButton("Add");
JButton subButton = new JButton("Subtract");
pane.setLayout(new GridLayout(4,2));
pane.add(new JLabel("Enter a number"));
pane.add(firstNumber);
pane.add(secondNumber);
pane.add(new JLabel("Result"));
pane.add(result);
pane.add(addButton);
pane.add(subButton);
DoMath listener = new DoMath(firstNumber, secondNumber, result);
subButton.addActionListener(listener);
addButton.addActionListener(listener);
frame.pack();
frame.show(); }
RECAP

4. RECAP // DoMath.java import javax.swing.*; import java.awt.event.*;
class DoMath implements ActionListener{
DoMath(JTextField first, JTextField second, JTextField result){
inputOne = first;
inputTwo = second;
output = result; }
public void actionPerformed(ActionEvent e){
double first, second;
first = Double.parseDouble(inputOne.getText().trim());
second = Double.parseDouble(inputTwo.getText().trim());
if (e.getActionCommand().equals("Add"))
output.setText(String.valueOf(first+second));
else
output.setText(String.valueOf(first-second));
private JTextField inputOne, inputTwo, output;

5. Running the application

6. Drawing in a frame
We will use the graphics and the Jframe together with a simple loop that creates references for a line.
The line needs a starting x,y coordinate and an ending ending x,y coordiante
We will use the class Star for definition and the class StartTest for executing our star

7. Drawing in a frame Importing the libraries
// StarTest.java - display a starburst
import java.awt.*;
import javax.swing.*;
class StarTest{
public static void main (String[] args){
JFrame frame = new JFrame("StartTest");
Container pane = frame.getContentPane();
Star star = new Star();
pane.add(star);
frame.pack();
frame.show(); }
Creating a class called StartTest
Creating a main section
Creating a frame named frame and labeled StarTest

8. Drawing in a frame // StarTest.java - display a starburst
import java.awt.*;
import javax.swing.*;
class StarTest{
public static void main (String[] args){
JFrame frame = new JFrame("StartTest");
Container pane = frame.getContentPane();
Star star = new Star();
pane.add(star);
frame.pack();
frame.show(); }
Creating a container named pane, and associating it with our frame called frame.
Creating an object named star based on the definition of Star (our class we will cover later)
Adding our star to the container for our frame

9. Drawing in a frame // StarTest.java - display a starburst
import java.awt.*;
import javax.swing.*;
class StarTest{
public static void main (String[] args){
JFrame frame = new JFrame("StartTest");
Container pane = frame.getContentPane();
Star star = new Star();
pane.add(star);
frame.pack();
frame.show(); }
Packing the frame to smallest size
Showing the frame

10. The Star Class Importing the libraries
// Star.java - draws a star
import javax.swing.*;
import java.awt.*;
class Star extends JComponent{
public void paint (Graphics g){
double x1, x2, y1, y2;
for (double angle=0; angle<Math.PI;
angle = angle + Math.PI / 16) {
x1=Math.cos(angle) * RADIUS + RADIUS;
y1=Math.sin(angle) * RADIUS + RADIUS;
x2=Math.cos(angle + Math.PI) * RADIUS + RADIUS;
y2=Math.sin(angle + Math.PI) * RADIUS + RADIUS;
g.drawLine((int)x1, (int)y1,(int)x2, (int)y2); }
public Dimension getMinimumSize(){
return new Dimension(2 * RADIUS, 2 * RADIUS);
public Dimension getPreferredSize(){
private static final int RADIUS = 100;
Importing the libraries
Creating a derived class based on the class called JComponents from the library
Creating a public class named paint using the Graphics features

11. Drawing in a frame Creating four variables:
// Star.java - draws a star
import javax.swing.*;
import java.awt.*;
class Star extends JComponent{
public void paint (Graphics g){
double x1, x2, y1, y2;
for (double angle=0; angle<Math.PI;
angle = angle + Math.PI / 16) {
x1=Math.cos(angle) * RADIUS + RADIUS;
y1=Math.sin(angle) * RADIUS + RADIUS;
x2=Math.cos(angle + Math.PI) * RADIUS + RADIUS;
y2=Math.sin(angle + Math.PI) * RADIUS + RADIUS;
g.drawLine((int)x1, (int)y1,(int)x2, (int)y2); }
public Dimension getMinimumSize(){
return new Dimension(2 * RADIUS, 2 * RADIUS);
public Dimension getPreferredSize(){
private static final int RADIUS = 100;
Creating four variables:
x1 = starting coordinate for the line
y1 = starting coordinate for the line
x2 = ending coordinate for the line
y2 = ending coordinate for the line

12. Drawing in a frame A loop for drawing 16 lines
// Star.java - draws a star
import javax.swing.*;
import java.awt.*;
class Star extends JComponent{
public void paint (Graphics g){
double x1, x2, y1, y2;
for (double angle=0; angle<Math.PI;
angle = angle + Math.PI / 16) {
x1=Math.cos(angle) * RADIUS + RADIUS;
y1=Math.sin(angle) * RADIUS + RADIUS;
x2=Math.cos(angle + Math.PI) * RADIUS + RADIUS;
y2=Math.sin(angle + Math.PI) * RADIUS + RADIUS;
g.drawLine((int)x1, (int)y1,(int)x2, (int)y2); }
public Dimension getMinimumSize(){
return new Dimension(2 * RADIUS, 2 * RADIUS);
public Dimension getPreferredSize(){
private static final int RADIUS = 100;
A loop for drawing 16 lines
Fancy math using the Math class for finding the endpoints and start points of the line to be drawn

13. Drawing in a frame Drawing the line.
// Star.java - draws a star
import javax.swing.*;
import java.awt.*;
class Star extends JComponent{
public void paint (Graphics g){
double x1, x2, y1, y2;
for (double angle=0; angle<Math.PI;
angle = angle + Math.PI / 16) {
x1=Math.cos(angle) * RADIUS + RADIUS;
y1=Math.sin(angle) * RADIUS + RADIUS;
x2=Math.cos(angle + Math.PI) * RADIUS + RADIUS;
y2=Math.sin(angle + Math.PI) * RADIUS + RADIUS;
g.drawLine((int)x1, (int)y1,(int)x2, (int)y2); }
public Dimension getMinimumSize(){
return new Dimension(2 * RADIUS, 2 * RADIUS);
public Dimension getPreferredSize(){
private static final int RADIUS = 100;
Drawing the line.
This requires 4 points and they need to be integers, so we cast these variables as integers (they are actually doubles)

14. // Star.java - draws a star
import javax.swing.*;
import java.awt.*;
class Star extends JComponent{
public void paint (Graphics g){
double x1, x2, y1, y2;
for (double angle=0; angle<Math.PI;
angle = angle + Math.PI / 16) {
x1=Math.cos(angle) * RADIUS + RADIUS;
y1=Math.sin(angle) * RADIUS + RADIUS;
x2=Math.cos(angle + Math.PI) * RADIUS + RADIUS;
y2=Math.sin(angle + Math.PI) * RADIUS + RADIUS;
g.drawLine((int)x1, (int)y1,(int)x2, (int)y2); }
public Dimension getMinimumSize(){
return new Dimension(2 * RADIUS, 2 * RADIUS);
public Dimension getPreferredSize(){
private static final int RADIUS = 100;
The class JComponent includes definitions of these methods which by default returns the value of 0. Here we redefine those methods so that the layout manager provides an area large enough for the whole star to show. The class Dimension is a standard java class that simple encapsulates two integers treated as height and width.
When the method pack is called for a JFrame the layoutmanager of the content pane will call one of the methods getMinimumSize() or getPreferredSize(). The call depends on the Layout manager and other factors. The value returned is used to determine the location and size.

15. Drawing in a frame

16. Drawing in a frame
We used the graphics and the Jframe together with a simple loop that creates references for a line.
The line needs a starting x,y coordinate and an ending ending x,y coordiante
We used the class Star for definition and the class StartTest for executing our star
We manipulated the container manager