JAVA Programming

1
JAVA Programming

• Part II - Review

2
Is A Relationship

• Relies on inheritance
• This one thing is a type of this other thing.
• Keyword extends
• A class is tightly encapsulated if it protects
  the objects data by forcing calling code to use
  methods instead of directly accessing instance
  variables.
• public class Car
• public class Subaru extends Car

3
OO Terms

• public class Vehicle
• public class Car extends Vehicle
• public class Subaru extends Car
• Vehicle is the superclass of Car
• Car is the subclass of Vehicle
• Car is the superclass of Subaru
• Subaru is the subclass of Vehicle
• Vehicle is the parent class of Car
• Car is the child class of Vehicle
• Car is the parent of Subaru
• Subaru is the child of Car

4
Overridden Methods

• Benefit is to get behavior specific to a
  particular subclass type
• Abstract methods must be overridden unless the
  parent class is also abstract.
• The argument list must match exactly.
• The return type must match exactly.
• You cant override a method marked final().
• You cant override a method that cant be
  inherited. If the subclass does not have access
  to the superclass method because of access
  modifier restrictions.
• Invoke the superclass version of a particular
  method by using the keyword super.

5

• public class Animal
• public void PrintYourself( )
• public class Dog extends Animal
• public void PrintYourself( )
• super.PrintYourself( )

6
Overloaded Methods

• Reuse the same method name in a class but use
  different arguments
• Code takes on the burden of coping with different
  arguments rather than forcing the caller to have
  all the information needed for the method in a
  particular format
• Must change the argument list (by order, number,
  and/or type)
• The return types can vary.

7

• public class Dog
• int size
• String name
• int numOfSpots
• public void change(int size, String name)
• this.size size
• this.name name
• public void change(int size, String name, int
  numOfSpots)
• this.size size
• this.name name
• this.numOfSpots numOfSpots

8
Varying Return Types

• class Adder
• public int addNums(int x, int y)
• return xy
• public double addNums(double x, double y)
• return xy

9
Constructors

• Invoked whenever you say new
• Main purpose is to let you initialize the
  objects instance variables
• A constructors name must exactly match the name
  of the class.
• Constructors must not have a return type.
• Methods can have the same name as the constructor
  as long as the method has a return type.
• A call to a super constructor can be no-arg or
  include arguments passed to the super
  constructor.
• Overloading a constructor means typing in
  multiple versions of the constructor, each having
  different lists.

10

• class Dog
• Dog( )
• super(Fido)
• Dog(String name)
• System.out.println(name)

11

• Which statements identify that a pancake is a
  food?
• Class Pancake extends class Food
• Class Food extends class Pancake
• Class Pancake is in the package Food
• Class Pancake has a reference to a Food
• Class Food has a reference to a Pancake
• Identify whether the following methods would be
  legal in a subclass of Foo.
• class Foo
• String doStuff(int x)
• String doStuff(int x)
• int doStuff(int x)
• public String doStuff(int x)
• String doStuff(String s)
• What if the doStuff method was modified to a
  public class?
• public String doStuff(int x)

12

• Which of the following are legal constructors
  that can be added to the Beagle subclass of Dog?
• No constructor, allow the compiler default
• Beagle()super()
• Beagle()super(fido)
• Beagle()
• Would the following code compile? Why or why
  not?
• public class Animal
• private Animal( )
• public class Dog extends Animal

13

• What will be the result of the following program?
• public class Demo
• public static void main(String args)
• int i 1
• if (i 0)
• if (i 2)
• if (i 4)
• System.out.println(big number)
• else
• System.out.println(not so big number)
• else
• System.out.println(small number)

14

• What will be the result of the following program?
• public class Demo
• public static void main(String args)
• char test 3
• switch (test)
• case 3
• System.out.println(third case)
• default
• System.out.println(default)
• case 2
• System.out.println(second case)
• break
• case 1
• System.out.println(first case)

15
JComponent class

• Basis of the GUI in Java application
• Anything that can be seen or used in an
  application is a subclass of JComponent
• Base class for all classes in the AWT with
  graphical representations
• Use methods setVisible(false) and
  setVisible(true) to control visibility.
• Use method setEnabled(false) grays out a
  component and makes it not functional
• Use setFont method to set the name, style, and
  the size.
• Styles Font.Plain, Font.Bold, Font.Italic,
  Font.BoldFont.Italic
• Font myFont new Font(SansSerif,
  Font.Bold,28)
• myComponent.setFont(myFont)

16
JTextField

• Input field with only one line
• JTextField textField1 new JTextField(20)
• Blank field of 20 columns
• JTextField textField2 new JTextField()
• Blank text field
• JTextField textField3 new JTextField(Yes)
• Predefined text displayed
• JTextField textField4 new JTextField(Both,30)
  
• Predefined text in 30 columns

17
JTextArea

• Multiple lines of text that allow the setting of
  the width and the height of the viewing area of
  the text
• JTextArea textArea
• JTextArea textArea new JTextArea(5, 20)
• textArea.setEditable(false)
• JScrollPane scrollPane new
  JScrollPane(textArea,
  JScrollPane.VERTICAL_SCROLLBAR_ALWAYS,
  JScrollPane.HORIZON
  TAL_SCROLLBAR_ALWAYS)
• JTextArea textArea2 new JTextArea(Once upon
  a time)
• JTextArea textArea3 new JTextArea(Once upon
  a time, 4, 60)
• JTextArea textArea4 new JTextArea(Once upon
  a time, 4, 60, JTextArea.SCROLLBARS_BOTH)

18
JLabel

• public LabelDemo()
• ImageIcon icon new ImageIcon("images/mid
  dle.gif",
• "a pretty
  but meaningless splat")
• setLayout(new GridLayout(3,1)) //3
  rows, 1 column
• JLabel label1 new JLabel("Image and Text",
  icon, JLabel.CENTER)
• label1.setVerticalTextPosition(JLabel.BOTTOM)
  
• label1.setHorizontalTextPosition(JLabel.CENTE
  R)
• JLabel label2 new JLabel("Text-Only Label")
• JLabel label3 new JLabel(icon)
• add(label1)
• add(label2)
• add(label3)

19
JCheckbox

• JCheckbox chinButton new JCheckbox("Chin")
  chinButton.setMnemonic(KeyEvent.VK_C)
  chinButton.setSelected(true)
• JCheckbox glassesButton new
  JCheckBox("Glasses") glassesButton.setMnemonic(Ke
  yEvent.VK_G)
• glassesButton.setSelected(true)
• JCheckbox hairButton new JCheckBox("Hair,
  true) hairButton.setMnemonic(KeyEvent.VK_H)
  hairButton.setSelected(true)

20

• JList list new JList(imageList)
  list.setSelectionMode(ListSelectionModel.SINGLE_SE
  LECTION)
• SINGLE_SELECTION
• Only one item can be selected at a time. When the
  user selects an item, any previously selected
  item is deselected first.
• SINGLE_INTERVAL_SELECTION
• Multiple, contiguous items can be selected. When
  the user begins a new selection range, any
  previously selected items are deselected first.
• MULTIPLE_INTERVAL_SELECTION
• The default. Any combination of items can be
  selected. The user must explicitly deselect
  items.
• listModel.addElement("Alison Huml")
• listModel.addElement("Kathy Walrath")
• listModel.addElement("Lisa Friendly")

21
Events

• Package java.awt.event
• When interfacing with a user at a keyboard, there
  is a method detected by the o/s to determine what
  the user is doing.creating an event
• The AWTEvent holds the info concerning the type
  of event.
• Any object can be notified of the event. All it
  has to do is implement the appropriate interface
  and be registered as an event listener on the
  appropriate event source.
• If the interaction was performed with a mouse, a
  MouseEvent is created.
• If the interaction was performed with a keyboard,
  the KeyEvent is created.
• If the interaction was performed on a window, a
  WindowEvent is created.

22

• Action Event and Associated Listener
• User clicks a button
• ActionListener
• User closes a frame (main window)
• WindowListener
• User presses a mouse button while the cursor is
  over a component
• MouseListener
• User moves the mouse over a component
• MouseMotionListener
• Component becomes visible
• ComponentListener
• Component gets the keyboard focus
• FocusListener
• Table or list selection changes
• ListSelectionListener

23
How To Implement an Event Handler

• Every event handler requires three bits of code
• In the declaration for the event handler class,
  code that specifies that the class either
  implements a listener interface or extends a
  class that implements a listener interface.
• public class MyClass implements ActionListener
• Code that registers an instance of the event
  handler class as a listener upon one or more
  components. someComponent.addActionListener(instan
  ceOfMyClass)
• Code that implements the methods in the listener
  interface. public void actionPerformed(ActionEvent
  e) ...//code that reacts to the action...

24
JButton Event Example

• To detect when the user clicks an on-screen
  button (or does the keyboard equivalent), a
  program must have an object that implements the
  ActionListener interface.
• The program must register this object as an
  action listener on the button (the event source),
  using the addActionListener method.
• When the user clicks the on-screen button, the
  button fires an action event. This results in the
  invocation of the action listener's
  actionPerformed method (the only method in the
  ActionListener interface).
• The single argument to the method is an
  ActionEvent object that gives information about
  the event and its source.

25
Multiple Listeners

• It is possible to have one listener and add that
  listener to lots of components and let that
  listener determine which component it is dealing
  with.
• Listener needs to know which component fired the
  event.
• Listener uses the getSource method to determine
  which component fired the event.

26
Multiple Button Listener Example

• import java.awt.
• import java.awt.event.
• class Test extends Frame implements
  ActionListener
• JButton b1 new JButton(Close)
• JButton b2 new JButton(Write to console)
• public Test()
• this.setLayout(new FlowLayout())
• b1.addActionListener(this)
• b2.addActionListener(this)
• this.add(b1)
• this.add(b2)
• this.setSize(300, 100)
• this.setVisible(true)

public void actionPerformed(ActionEvent e)
if (e.getSource( ) b1)
System.exit(0) if (e.getSource() b2)
System.out.println(Button b2 was
pushed) public static void main(String
args) Test t new Test()
27
KeyEvent Constants

• Set of constants built-in to relate to the
  KeyCode for all the possible inputs on a
  keyboard.
• KeyTyped of a capital A requires a keyPressed of
  SHIFT and a keyPressed of a

28

• import java.awt.event.
• class MyListener implements KeyListener
• public void keyPressed(KeyEvent e)
• System.out.println(A key was pressed)
• public void keyRelease(KeyEvent e)
• System.out.println(A key was release.)
• public void keyTyped(KeyEvent e)
• System.out.println(A key was Typed)

29

• import java.awt.
• import java.awt.event.
• class Test
• public static void main(String args)
• Jframe f new Jframe(test)
• JTextField t new JTextField(This is the
  default)
• MyListener lis new MyListener()
• t.addKeyListener(lis)
• f.add(t)
• f.setSize(400,300)
• f.setVisible(true)

30

• What happens when the following code is executed?
• import java.awt.
• import java.swing.
• class Test extends JFrame
• JButton b1, b2, b3
• Test()
• JButton b1 new JButton(b1)
• JButton b2 new JButton(b2)
• JButton b3 new JButton(b3)
• add(b1)
• add(b2)
• add(b3)
• this.setSize(400, 200)
• this.setVisible(true)
• public static void main(String args)
• Test t new Test()

31

• Write the syntax to add a Checkbox named Maple to
  a Checkboxgroup named Trees and set it to a
  default to checked. There are 2 ways to
  accomplish this.
• What happens if you create a JTextField on a
  Panel using new JTextField(Enter values) and
  the user enters a long String?

32

• What is the output of the following code?
• import java.awt.
• import java.awt.event.
• class Test extends Frame
• MyListener lis new MyListener()
• public Test()
• this.addKeyListener(lis)
• this.setSize(400, 400)
• this.setVisible(true)
• public static void main(String args)
• Test t new Test()
• class MyListener extends KeyAdapter
• public void KeyPressed(KeyEvent e)
• System.out.println(got e.getKeyChar())