Chapter 4 Revision Tour 2

CHAPTER-4

JAVA GUI PROGRAMMING REVISION TOUR - II [Swing Controls]

Brief Summary of the Chapter:

In this chapter we shall be revising the JAVA GUI programming concepts using Swing API through NetBeans IDE.Java GUI applications are created through RAD tools with   Classes, Object and
methods etc.

Key Points:

·   Swing API includes graphical components for building GUIs.

·   Swing components can be either container or non container component. ·   Swing provide seven different Layout manager.

·   Frame is a top level window with a title and a border, created through jFrame component of
      Swing.

·     Common properties of buttons are: background, border, font, foreground, enabled, Horizontal
      Alignment, Vertical Alignment.

·   Label control displays text, that the user can not changed directly. ·   Label is created through jLabel class component.
·   TextField is created through jTextField class component.

·   Password field takes input without showing it on the screen, created through jPasswordField
      class component.

·   TextArea is multiline component to display or enter text, created through jTextArea class
      component.

·   Checkbox is a rectangular area that can be chacked or unchecked created
      class component.

SOLVED QUESTIONS

1.What does getPassword() on a password field return?

(a) a string (b) an integer (c) a character array. Ans: (c) a character array

2. Which of the following component is the best suited to accept the country of the user?

A.  List   B. Combo box C. Radio button   D. Check box

Ans: B. Combo box

3. What command do you need to write in actionPerformed() event handler of a button, in order to make it exit button?

a. System.out.println(); b. System.exit(0);   c. System.out.print() Ans: b. System.exit(0);

4.What method would you use, in order to simulate a button’s(namely Okbtn) click event, without any mouse activity from user’s side?

a. Okbtn.setText() b.Okbtn.getText()   c. Okbtn.doClick() Ans: Okbtn.doClick()

5. What would be the name of the event handler method in the ListSelection listener interface for a list namely CheckList to handle its item selections?

a. CheckListValueChanged()   b. getSelectedValue() c. clearSelection() Ans: a. CheckListValueChanged()

6. Which control displays text that the user cannot directly change or edit?

a.TextField   b. Checkbox   c. Combobox d. Label

Ans: d.Label

7.Which control provides basic text editing facility?

a.TextField   b. Checkbox   c. Combobox d. Label Ans: a. TexfField

8. Occurrence of an activity is called:

a. Function   b. Class   c. Object   d. Event
Ans: d.Event.

9. Which property is used to set the text of the Label?

a. font b.text c.name d. icon

Ans: b.text

10. The object containing the data to be exhibited by the combo box by which property.

a. editable b. model c.selectedIndex d.selectedItem

Ans: b. model

11.   What is GUI programming?

Ans: A GUI(Graphical User Interface) is an interface that uses pictures and other graphic entities along with text, to interact with user.

12. How is swing related to GUI programming?

Ans: We can create a GUI application on Java platform using Swing API (Appli Interface), which is part of Java Foundation Classes(JFC).

13. What is an event? What is event handler?

Ans: An event is occurrence of some activities either initiated by user or by the system. In order to react, you need to implement some Event handling system in your Application. Three things are important in Even Handling-

Event Source: It is the GUI component that generates the event, e.g. Button.

Event Handler or Event Listener: It is implemented as in the form of code. It receives and handles events through Listener Interface.

Event Object or Message: It is created when event occurs. It contains all the information about the event which includes Source of event and type of

event etc.

14. What is the default name of action event handler of a button namely TestBtn?
Ans: private void TestBtnActionPerfomed(java.awt.action.ActionEvent evt){   }.

15. What property would you set to assign access key to a button?

Ans: mnemonic property is used to assign access key or shortcut (Alt + Key).

16. Which method can programmatically performs the click action of a push button?
Ans: private void TestBtnActionPerfomed(java.awt.action.ActionEvent evt){   }.

17. Which property would you set the setting the password character as ‘$’? Ans:echoChar

18. Which method returns the password entered in a password field? Ans: char [] getPassword().

19. Which list property do you set for specifying the items for the list. Ans: model

20. Which method would you use to determine the index of selected item in a list? Ans: int getSelectedIndex().

21. Which method would you use to insert an item at specified index, in the list? Ans:   void setSelectedIndex( int index).

22. How you can determine whether 5th item in a list is selected or not? Ans: isSelectedIndex(4).

23. Which method you would use to insert ‘Hello’ at 10th position in the Text Area control. Ans:void insert(“Hello”, 9).

24. Which method you would like to use to insert an Icon (picture) on a Push Button. Ans: void setIcon(Icon).

25. Which property would you like to set to make a Combo box editable? Ans: editable.

26. What is Layout Manager? Name the layout managers offered by NetBeans?

Ans: Layout managers enable you to control the way in which visual components are arranged in GUI forms by determining the size and position of components within containers.

There are seven types of layout are available-
      ·   Flow Layout

          Grid Layout

          Card Layout

          Spring Layout

          Border Layout

          GridBag Layout

          Box Layout

27. Name three commonly used properties and methods of the following controls.

(a) text field (b) text area (c) Check Box

Ans: (a) Properties: text, font, editable. Methods:   void setText(), String getText(), void setEditable(boolean).

(b) Properties: enabled, editable, wrapStyleWord Methods: setText(), getText(), isEditable()

(c) Properties:font, text, selected . Methods: getText(), isEnabled(), isSelected().

28. What is dispose() used for ?

Ans: dispose() is used for hide and dispose of the frame when the user closes it. This removes the frame from the screen and frees up any resources used by it.

29. What is the difference between-

(a) Text field & Text area

(b) Text field &  password field

(c) Radio Button & Check Box

Ans: (a) A text field’s text property can hold single line of text unless it is an HTML text. While a text area’s text can hold any number of lines of text depending upon its rows property.

(b) Though a text field   and a password field can obtain a single line of text from the user, yet these are different.

A password field displays the obtained text in encrypted form on screen while text field displays the obtained text in unencrypted form.

(c) Radio Button: A jRadioButton control belongs to JRadioButton class of Swing controls. It is used to get choices from the user. It is grouped control, so that only one can be selected at a time among them. Radio Button works in group, so that they must be kept in a ButtonGroup container control like so that only one can be selected at the same time.

Some features of jRadioButton control are-

It can be used to input choices typed input to the application. Only one Radio button can be selected at a time.

They must be kept in a Button Group container control to form a group.

Check box: A jCheckBox control belongs to JCheckBox class of Swing controls. It indicates whether a particular condition is on or off. You can use Check boxes to give users true/false or yes/no options. Check Boxes may works independently to each other, so that any number of check boxes can be
selected at the same time.

Some features of jCheckBox control are-

It can be used to input True/False or Yes/No typed input to the application. Multiple check boxes can be selected at the same time.

30. What is the significance of following properties of a text area ?

(a) lineWrap (b) wrapStyleword

Ans: (a) Defines Wrapping featureenable/disable (b) Determines where line wrapping occurs. If true, the component attempts to wrap only at word boundaries. This property is ignored unless linewrap is set to true.

31. What is the significance of a button group? How do you create a button group?

Ans:   We must add a ButtonGroup control to the frame to group the check boxes by using Button Group property of the check box. By dragging buttongroup control from palette window.

32. What do you understand by focus?

Ans: A Focus is the ability to receive user input/response through Mouse or Keyboard. When object or control has focus, it can receive input from user.

An object or control can receive focus only if its enabled and visible property are set to true.

Most of the controls provides FOCUS_GAINED() and FOCUS_LOST() method in FocusEvent by the FocusListener. FOCUS_LOST() is generally used for validation of data.
    You can give focus to an object at run time by invoking the requestFocus() method in the code.
Ex. jTextBox2.requestFocus();

33. What is meant by scope of a variable?

Ans: In Java, a variable can be declared any where in the program but before using them.

The area of program within which a variable is accessible, known as its scope. A variable can be accessed within the block where it is declared.