Swing GUI Components

1. Swing GUI Components You can create graphics components to place on your applet using classes available in the Swing package ( javax.swing ) Class names start with J : JTextField , JLabel, JButton Objects are created by calling a class constructor: JLabel xLabel = new JLabel("x = "); JTextField xField = new JTextField(width); JButton moveButton = new JButton("Move",buttonIcon); JButton anotherButton = new JButton(“go”);

2. use Control panel These components are placed in a control panel, a container for user interface components. JPanel thePanel = new JPanel (); thePanel.add(xLabel); thePanel.add(xField); thePanel.add(moveButton); thePanel.add(anotherButton); This panel can then be placed in a frame, and the frame shown. JFrame theFrame = new JFrame(); theFrame.setcontentPane(thePanel); theFrame.pack(); theFrame.show(); *it is possible to put the panel directly on the applet, but more GUI experience is needed …

3. public class myFrapp extends Applet { public myFrapp() { JLabel xLabel = new JLabel("x = "); //instantiate components JTextField xField = new JTextField(5); JLabel yLabel = new JLabel(“y = "); JTextField yField = new JTextField(5); JButton anotherButton = new JButton(“Go"); JPanel thePanel = new JPanel (); //place components on panel thePanel.add(xLabel); thePanel.add(xField); thePanel.add(yLabel); thePanel.add(yField); thePanel.add(anotherButton); JFrame theFrame = new JFrame(); //put panel in frame and show theFrame.setContentPane(thePanel); theFrame.pack(); //adjust components to framesize theFrame.show(); }

4. Let’s execute applet myFrapp so far…….. ( website: myFrapp1.java )

5. In order to recognize when the button is pressed, we need an event listener which is registered with the button !! public class myFrapp extends Applet{ public myFrapp() { //instantiate components NEW!! //create a listener class NEW!! //register a listener object with button component //place components on panel //put panel in frame and show }

6. Button clicks create ActionEvent objects A class which is to be used for creating action listener object must implement the ActionListener interface. *also in java.awt.event package The ActionListener interface contains one abstract method: void actionPerformed(ActionEvent event);

7. So our listener must implement the ActionListener interface. public class myFrapp extends Applet{ public myFrapp() { //instantiate components //create listener class class BtnListener implements ActionListener{ public void actionPerformed(ActionEvent e){ // code task to be done when button is pushed } } //register a listener object with button component ActionListener bltn = new BtnListener(); anotherButton.addActionListener(bltn); //place components on panel //put panel in frame and show }

8. Let’s finish our applet so that when the user presses the button, the values in the textfields are used to reposition a triangle on the applet.

9. A Triangle class would be helpful here, so assume: public class Triangle{ private double startx, starty; public Triangle(double sx, double sy) { startx = sx; starty = sy; } public void setTri( double sx, double sy){ startx = sx; starty = sy; } public void draw (Graphics2D g) { // code which draws a triangle at position (startx,starty) using // graphics environment g } }

10. //THIS WILL DRAW the first TRIANGLE public class myFrapp extends Applet{ private Triangle tri = new Triangle(50.00,50.00); public myFrapp() { //instantiate components //create a listener class //register a listener object with button component //place components on panel //put panel in frame and show } public void paint (Graphics g) Graphics2D g2 = (Graphics2D) g; tri.draw(g2); } //now we are ready to write that button listener

11. The button listener class…… class BtnListener implements ActionListener{ public void actionPerformed(ActionEvent e){ double newx = Double.parseDouble(xField.getText()); * double newy = Double.parseDouble(yField.getText()); tri.setTri(newx,newy); repaint(); } } • //register a listener object with button component • ActionListener bltn = new BtnListener(); • anotherButton.addActionListener(bltn); * If declared as local variables, must be declared as final………

12. Check that this runs correctly………. (website: myFrapp.java)

13. We now know all we need to write a frame application.. Examine the following applet:

14. public class myFrapp extends Applet { public myFrapp() { JLabel xLabel = new JLabel("x = "); //create gui components final JTextField xField = new JTextField(5); JLabel yLabel = new JLabel(“y = "); final JTextField yField = new JTextField(5); JButton anotherButton = new JButton(“Go"); //set up listener for button class BtnListener implements ActionListener{ public void actionPerformed(ActionEvent e){ int val1 = Integer.parseInt(xField.getText()); * int val2 = Integer.parseInt(yField.getText()); val1 = val1+val2; xField.setText(Integer.toString(val1)); } } ActionListener lstn = new BtnListener(); anotherButton.addActionListener(lstn);

15. // constructor continued JPanel thePanel = new JPanel (); //place components on panel thePanel.add(xLabel); thePanel.add(xField); thePanel.add(yLabel); thePanel.add(xField); thePanel.add(anotherButton); JFrame theFrame = new JFrame(); //put panel in frame and show theFrame.setContentPane(thePanel); theFrame.pack(); //adjust components to framesize theFrame.show(); } //end constructor } //end applet

16. Check that this runs correctly………. (website: Step1.java) We really didn’t need the applet at all…………..

17. This is what we have so far …….. • public class Step1 { public static void main (String [] args) { public Step1() { • //create gui components • //set up listener for button • //create panel • //place components on panel • //create frame • //put panel in frame and show • } • } public class Step1 extends Applet { now we have a frame application ……..

18. Check that this runs correctly………. (website: Step2.java) Now let’s provide a larger output area and customize the frame a bit………

19. Now the output is sent to a text area….. JLabel xLabel = new JLabel("x = "); final JTextField xField = new JTextField(width); JLabel yLabel = new JLabel("y = "); final JTextField yField = new JTextField(width); final JTextArea sumArea = new JTextArea(10,20); JButton anotherButton = new JButton("Go"); //create listener class class BtnListener implements ActionListener{ public void actionPerformed(ActionEvent e){ int val1 = Integer.parseInt(xField.getText()); int val2 = Integer.parseInt(yField.getText()); val1 = val1 + val2; sumArea.append("The result is: " + val1); } }

20. // put components on panel and set panel color to red //add components to panel JPanel thePanel = new JPanel (); thePanel.setBackground(Color.red); thePanel.add(xLabel); thePanel.add(xField); thePanel.add(yLabel); thePanel.add(yField); thePanel.add(anotherButton); thePanel.add(sumArea);

21. and program will now exit when frame is closed, Size the frame rather than pack, Set a background color for the frame (frame is UNDER the panel) Place the frame is a particular location JFrame theFrame = new JFrame(); theFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); Dimension dim = new Dimension(200,300); theFrame.setSize(dim); theFrame.setBackground(Color.cyan);//this is UNDER the panel theFrame.setLocation(0,0); theFrame.setContentPane(thePanel); theFrame.show();

22. Check that this runs correctly………. (website: Step3.java) Try packing the frame and see what happens……….