Using Objects Chapter 6 “CarCounter page 89 and 91 Local variables declared in a method only temporary carCount is a local variable good only while the method exists. It is an instance variable

Instantiation using random class Page 93 “RandomLines” Private Random randomPositions = new Random( ); –xEnd = randomPositions.nextInt (100); –Using the method to generate a number from the range 0 to 99

The Swing toolkit Imported as a Java library Components look the same on every platform (JButtons for example)

Events Action – like a button Change – adjust a slider “extends” current class (child) inherits from another class (parent)

Creating a JButton CarCounter extends JFame page 99 Private JButton button; button = new JButton (“Car Enterng”); –Window.add(button); When button clicked actionListener called

General Guides for using objects 1.Determine what is to be imported 2.Select a constructor (with “new”) to be used 3.Add window, if needed 4.Use the instance via it’s methods

Page 102 SumTextFields uses JLabel class to display non- changing text fields private JTextField number1Field, number2Field, sumField; JTextField class –A single line area to display text or input text – textField1 = new JTextField(15); –textField2 = new JTextField(“Hello!”,15); –String s; – s = textField1.getText( ); –textField1.setText(s);

JPanel class Used for drawing, or to hold objects such as buttons panel = new JPanel( ); –Panel.setPreferedSize(new Dimension(200,200)); – window.add(panel);

Timer class Regularly spaced events timers, control speeds Not visible as Buttons are

TimerExample page 105 Screenshot shows number of seconds Using timer.

JSlider “Raindrops” page 107 private JSlider slider; slider = new JSlider(JSlider.HORIZONTAL, 200, 2000, 1000); window.add (slider); … gapField = new JTextField(10); gapField.setText(Integer.toString ( slider.getValue( ) ) );

Summary The Java language has a vast number of classes which you can (and ought to) use. Do not write your own code without investigating the libraries first. You may check and search tutorials and references about the various classeshttp://