Basic GUI

Question 1

What form of programming do graphical user interfaces tend to use?

Answer 1

Event-driven programming

Question 2

What are the GUI packages used in Java?

Answer 2

AWT is the older framework. It involves “heavy-weight” components that use native system GUI elements

Swing is the newer version. Most components are lightweight.

Question 3

What are heavyweight GUI components?

Answer 3

Those that use native system GUI elements

Question 4

What is the naming convention for Java GUI frameworks?

Answer 4

AWT elements have no prefix i.e. “Component”

Swing components use J as a prefix i.e. “JComponent”

Question 5

What are the basic GUi components?

Answer 5

Windows - top level containers i.e. frame and dialog box

Components - GUI widgets i.e. button, label

Containers - logical grouping for components i.e panel

Question 6

How are dialog boxes created?

Answer 6

Using the static methods of JOptionPane i.e. .showInputDialog(“…”) and .showMessageDialog(null, “…”)

Question 7

How does the showInputDialog static method work?

Answer 7

Returns the string that the user enters or null if they press cancel.

Question 8

How does the showMessageDialog static method work?

Answer 8

First argument is where to display the alert. Use null for centre.

The second argument is the message to display.

Third argument is the title

Fourth is the type of message to display, using enums i.e. JOptionPane.ERROR_MESSAGE

Question 9

What GUI component allows colours to be selected? What does it return?

Answer 9

JColorChooser.

It returns a color of type Color, or null if the user presses cancel

Question 10

What is a frame?

Answer 10

A frame (i.e. JFrame) is a graphical window that holds other components. It includes a border and title bar.

The visible area of the Frame is a Container. It can be accessed by calling getContentPane()

Question 11

How are components added to a frame?

Answer 11

getContentPane().add(component)

This returns a Container

Question 12

What are the steps for creating a new frame?

Answer 12

// Create it
JFrame frame = new JFrame()

// Set close operation
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE)

// add components
frame.getContentPane().add(...)

// make it visible

frame. setSize(400, 200)
frame. setVisible(true)

Question 13

What GUI component is used to group GUI elements?

Answer 13

A JPanel

Question 14

How are components added to panels?

Answer 14

With .add() i.e. panel.add(new JButton(“OK”))

Question 15

How are labels created?

Answer 15

JLabel label = new JLabel(“Hello”)

Question 16

How are buttons created?

Answer 16

JButton button = new JButton(“hello”)

Question 17

What are layout managers?

Answer 17

Layout managers arrange GUI elements in a container for layout purposes i.e. to support resizing.

They implement the LayoutManager interface

Question 18

How is the layout manager specified?

Answer 18

Container pane = getContentPane();
pane.setLayout(new FlowLayout())

Question 19

What does the BorderLayout layout manger do?

Answer 19

Allows elements to be placed at the top (PAGE_START), bottom (PAGE_END), left (LINE_START), right (LINE_END) or middle (CENTER)

Components can be added to the pane with pane.add(button, BorderLayout.PAGE_START) once the layout manager of the pane has been set.

Question 20

How can the position of components in a BorderLayout manager be specified?

Answer 20

.add(component, BorderLayout.CENTER) is preferred. However, these arguments can be reversed or .add(“Centre”, button) can be used

Question 21

What does the FlowLayout manager do?

Answer 21

It places components over several lines from left-to-right, top-to-buttom.

The default constructor is centre aligned; FlowLayout.RIGHT or .LEFT can be used to right/left align

Question 22

How can custom painting inside a JPanel be implemented?

Answer 22

By overriding paintComponent(Graphics g)

n.b. this method is called automatically by the Java runtime when the frame is first displayed, resized, or covered and then returned to (some platforms)

Question 23

What are the basic graphics methods?

Answer 23

dawLine(), drawRect(), fillRect(), drawOval(), fille(Oval), drawString() etc.

n.b. drawABC() is jus the outline, fillABC() fills it in

setStroke() changes the BasicStroke. Use setPaint() to change the color i.e. Color.RED

Question 24

What are the basic types of nested classes?

Answer 24

Static and Non-Static (Inner class)

Question 25

What access does an inner class have?

Answer 25

Complete accès to the field and methods of an enclosing class, even if they are declared private

Question 26

Where are inner classes saved after compilation?

Answer 26

In their own .class file i.e. OuterClass$InnerClass.class

Question 27

Why are nested classes used?

Answer 27

They logically group classes that are only used in one place. This increases encapsulation and makes code more readable/maintainable

Question 28

How do static nested classes work?

Answer 28

The nested class can be used to make the objects of the nester class independent from the objects of the enclosing class

It can access static members and variables of its outer class (even if private). However, it cannot refer to instance members.

The outer class has full access to the static nested class.

It can also be instantiated/accessed without an instance of the outer class.

NOTE: You still instantiate it (super weird?)

Question 29

Can you instantiate static classes?

Answer 29

Only if they are inner classes!!!!!!!

Question 30

Terst

Answer 30

Test

Question 31

What are inner classes and what types do they come in?

Answer 31

They are non-static classes i.e. those that are associated with an instant of the outer class.

Member class: defined within the body of a class
Local class: defined within the method of a class
Anonymous class: local class that is declared implicitly by creating a variable of it

Question 32

What are member classes?

Answer 32

They are not declared static and are declared in the body of a class.

They cannot declare static variable and methods. They have access to all instance and class variables and objects of the outer class / any other inner classes.

The outer class has access to all variables and methods in the inner class

Question 33

What are local classes?

Answer 33

They are defined within a method and exist only until the end of that method/block.

Thy are never declared with access modifiers - scope is always restricted to their block. They cannot include static variables or methods.

They can access the fields of the containing class and the local variables of the method they are declared in.

Question 34

What kind of inner nested classes can be interfaces?

Answer 34

Only static members

Question 35

What kind of inner nested classes can be interfaces?

Answer 35

Only static members

Question 36

What methods are required to implement ActionListeners?

Answer 36

actionPerformed(ActionEvent e)

Question 37

What methods are required to implement ActionListeners?

Answer 37

actionPerformed()

Question 38

How are action listeners registered?

Answer 38

First create an instance as a variable, such as an anonymous class.

Then register it with component.addActionListener(handler);

Question 39

How is the text on buttons/labels edited?

Answer 39

With getText() and setText()

Question 40

What are the components for text entry?

Answer 40

JTextField is single line, JTextArea is multiple lines.

Where colours in the number of letters, they are created with:

JTextField(int columns) and JTextArea(int lines, int columns)

Question 41

How are strings made uppercase?

Answer 41

With stringVar.toUpperCase(). This returns the result.