Chapter 17 - GUI Components

Question 0

How do you group radio buttons together?

Answer 0

Use the ButtonGroup class:
ButtonGroup group = new ButtonGroup();
group.add(jrbName1);
group.add(jrbName2);

Question 1

What events are fired from JCheckBox and JRadioButton?

Answer 1

When clicked, first an ItemEvent is fired, then an ActionEvent

Question 2

How do you set mnemonic keys for check boxes and the likes?

Answer 2

By using the setMnemonic method provided by these classes.
jchkName.setMnemonic(‘N’);
Notice that the method takes a character as input (not a string!)

Question 3

When does a JTextField usually fire an action event?

Answer 3

After the “enter” key on the keyboard is pressed (if the text field is in focus, that is).

Question 4

What component do you use if you need to let the user enter multiple lines of text?

Answer 4

You use the class JTextArea

Question 5

JTextField and JTextArea inherits JTextComponent. What are the methods inherited from JTextComponent?

Answer 5

getText, setText, isEditable and setEditable

Question 6

JTextArea does not handle scrolling. How do you add scrolling to s JTextArea?

Answer 6

You use the class JScrollPane.
Let’s say you have a JTextArea named jtaName. You add scrolling like this:
JScrollPane scrollPane = new JScrollPane(jtaName);
The object scrollPane is now a text area with scrolling.

Question 7

What components can you put in a JScrollPane? What does JScrollPane do?

Answer 7

You can add any swing GUI components. JScrollPane adds horizontal and vertical scrolling if the component is too large to fit.

Question 8

What is a JComboBox? What is it good for?

Answer 8

Also known as a choice list or drop-down menu.

It’s useful for limiting the user’s range of choice, and avoids the cumbersome validation of data input.

Question 9

How do you code a JComboBox with 4 generic items, blue foreground color, white background color, and item 3 selected as default?

Answer 9

JComboBox jcb = new JComboBox(new Object[] {“item 1”, “item 2”, “item 3”, “item 4”});

jcb. setForeground(Color.blue);
jcb. setBackground(Color.white);
jcb. setSelectedItem(“item 3”);

Question 10

When does a JComboBox fire an ActionEvent?

Answer 10

Whenever an item is selected

Question 11

When does a JComboBox fire an ItemEvent?

Answer 11

When a new item is selected JComboBox fires ItemEvent twice. Once for deselecting the previously selected item, and once for selecting the new item.

Question 12

How is a JList different from a JComboBox?

Answer 12

A JList is basically the same as a JComboBox, but it has 3 selection modes:

1. Single selection; the same as JComboBox, only one item can be selected at a time.
2. Single interval selection; can select multiple items at once as long as they’re in one contigous interval
3. Multiple interval selection; can select multiple items in multiple intervals.

Question 13

What method must item listeners implement?

Answer 13

They must implement itemStateChanged(ItemEvent e) to respond to item events.

Question 14

What event does a JList fire, and what method must the listener of the corresponding interface implement to process the event?

Answer 14

JList fires a ListSelectionEvent. The ListSelectionListener must implement the method valueChanged(ListSelectionEvent e) to process the event.

Question 15

What is the difference between a JScrollPane and a JScrollBar?

Answer 15

A JScrollPane is a container that handles scrolling for components inside the container. A JScrollBar is the component used in JScrollPane (and anywhere else) that facilitates scrolling

Question 16

There are 3 ways a user can change the value of a scroll bar by using the mouse. What are they?

Answer 16

The user can:

1. click on the unit increment/decrement buttons at the ends of the scroll bar.
2. Drag the “bubble” back and forth.
3. Click on the space between the bubble and the unit incr/decr buttons to “block incr/decr”.

Question 17

When the value of a JScrollBar is changed, what event is fired?

Answer 17

An AdjustmentEvent

Question 18

What handler method must an AdjustmentListener implement?

Answer 18

The adjustmentValueChanged handler

Question 19

What is the difference between JSlider and JScrollBar?

Answer 19

They are similar, but JSlider has more properties and can appear in many forms. JScrollBar is typically used for scrolling, while JSlider is used for selecting between a range of values.

Question 20

What are the properties / data fields of javax.swing.JSlider, and what do they represent?

Answer 20

maximum (int): max value represented by slider (default = 100).

minimum (int): min value represented by slider (default = 0).

value (int): current value represented by slider.

orientation (int): orientation of slider (default = JSlider.HORIZONTAL).

paintLabels (boolean): true if labels are painted at tick marks (default = false).

paintTicks (boolean): true if ticks are painted on the slider (default = false).

paintTrack (boolean): true if track is painted on the slider (default = true).

majorTickSpacing (int): number of pixels between major ticks (default = 0).

minorTickSpacing (int): number of pixels between minor ticks (default = 0).

inverted (boolean): true to reverse the value range (default = false).

Question 21

When the value of a JSlider is changed, when event is fired by the slider?

Answer 21

ChangeEvent

javax.swing.event.ChangeEvent

Question 23

What method must a ChangeListener implement to handle a ChangeEvent?

Answer 23

It must implement stateChanged.

stateChanged(ChangeEvent e).

Question 24

Clicking a JCheckBox object generates \_\_\_ events.
A. ActionEvent
B. ItemEvent
C. ComponentEvent
D. ContainerEvent

Answer 24

A and B are correct

Question 25

The method \_\_\_\_ adds a text area jta to a scrollpane jScrollPane.
A. jScrollPane.add(jta)
B. jScrollPane.insert(jta)
C. jScrollPane.addItem(jta)
D. None of the above.

Answer 25

A is correct

Question 26

How many items can be added into a JComboBox object?
A. 0
B. 1
C. 2
D. Unlimited

Answer 26

The correct answer is D. Unlimited

Question 27

\_\_\_ returns the selected item on a JComboBox jcbo.
A. jcbo.getSelectedIndex()
B. jcbo.getSelectedItem()
C. jcbo.getSelectedIndices()
D. jcbo.getSelectedItems()

Answer 27

The correct answer is

B. jcbo.getSelectedItem()

Question 28

The method \_\_\_ adds an item s into a JComboBox jcbo.
A. jcbo.add(s)
B. jcbo.addChoice(s)
C. jcbo.addItem(s)
D. jcbo.addObject(s).

Answer 28

The correct answer is

C. jcbo.addItem(s)

Question 29

Clicking a JComboBox object always generates \_\_\_ events.
A. ActionEvent
B. ItemEvent
C. MouseEvent 
D. KeyEvent
E. WindowEvent

Answer 29

The correct answer is A and C.
Explanation: It generates ActionEvent and MouseEvent. Note that any GUI component fires a MouseEvent when mouse is clicked on the component. No ItemEvent is generated if the current item is re-selected.

Question 30

Clicking a JComboBox object generates an ItemEvent event,
A. if an item is selected.
B. if a new item is selected.

Answer 30

B. if a new item is selected.

Question 31

\_\_\_\_ is a component that enables the user to choose a single value or multiple values.
A. A text field
B. A combo box
C. A list
D. A label

Answer 31

The correct answer is

C. A list

Question 32

Clicking a JList object generates \_\_\_\_ events.
A. ActionEvent and ItemEvent
B. ItemEvent and ComponentEvent
C. ComponentEvent and ContainerEvent
D. ActionEvent and ContainerEvent

Answer 32

A. ActionEvent and ItemEvent

Question 33

Which of the following statements are true?
A. Every Swing GUI component has a default constructor.
B. You can create a scroll bar by specifying its orientation.
C. JScrollBar fires an ActionEvent.
D. JScrollBar fires an AdjustmentEvent.
E. A listener of a JScrollBar must implement AdjustmentEvent and the adjustmentValueChanged method.

Answer 33

A, B, D and E are true

Question 34

Which of the following statements are true?
A. You can create a JSlider bar by specifying its orientation.
B. JSlider fires an ActionEvent.
C. JSlider fires an AdjustmentEvent.
D. JSlider fires a javax.swing.event.ChangeEvent.
E. A listener of a JSlider must implement ChangeEvent and the stateChanged method.

Answer 34

All but C are true

Question 35

The following are properties of a JSlider.
A. minimum
B. maximum 
C. orientation
D. visibleAmount

Answer 35

All but D are correct

Question 36

Can you get the height and width of a window before the frame is created?

Answer 36

No!

Question 37

How can you get the height and width of a window after it is resized?

Answer 37

You can add a ComponentListener to the frame. For example, an instance of the following class can be added to a frame to change and repaint it every time it’s resized:

class WindowResizeListener extends ComponentAdapter {
@Override
public void componentResized(ComponentEvent e) {
messageY = (getHeight() / 6);
repaint();
}
}

Question 38

Describe in a few steps how to make a program show multiple windows / create subwindows.

Answer 38

1. Create a class for the main window, and a class for the subwindow.
2. Create an instance of the subwindow class in the main class.
3. In the main class, create a JFrame to hold the subwindow panel (unless the subwindow itself is a JFrame).
4. In the listener you want to create the subwindow, do operations you want performed by the subclass, and set the JFrame that holds the subwindow to visible.
5. In the constructor of the main class, add the subwindow panel, and do preferred operations on the frame, like:
   frame. setTitle(“asdg”);
   frame. pack();
   frame. awdgfawertw