Swing - GUI

Question 1

event driven programming

Answer 1

flow of the program is determined by events such as user actions, sensor outputs, or messages from other programs or threads

• signal and response approach
• exception handling is an example

Question 2

what is a GUI

Answer 2

graphical user interfaace - windowing system that interacts with the user

Question 3

awt

Answer 3

abstract window tool kit - original package in java for creating gui - swing now used generally

Question 4

event

Answer 4

an object that acts as a signal to another object - called a listener

Question 5

firing an event

Answer 5

sending an event - often a gui component - e.g. button clicked

Question 6

listener

Answer 6

listener object performs some action in response to the event - one big listener or individual listeners

Question 7

example of events

Answer 7

exception objects - throwing of an exception - the listener for an exception is the catch block that catches the event

Question 8

event handlers

Answer 8

methods that specify what will happen when the events of various kinds are received by it - the programmer using the listener object will define or redefine these event-handlers

Question 9

difference between event driven programming and what we’ve been doing…

Answer 9

• objects are created that can fire events and listener objects are created that can react to these events
• events determine the order in which things happen

in particular - methods are defineed that will never be explicitly invoked in any program - methods are invoked when an event signals that the method needs to be called

Question 10

JFrame

Answer 10

a simple window consists of an object of this class
- border and usual 3 buttons

JFrame newFrame = new JFrame (size, size);

Question 11

adding to and setting visibility of JFrame and setting close

Answer 11

newFrame.add(endButton);
newFrame.setVisible(true);
newFrame.serDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

Question 12

pixel

Answer 12

smallest unit of space on screen - size and position of swing objs measured in pixels

Question 13

what happens if you don’t program

Answer 13

default - hide on close

- doesnt close the program - memory and battery

Question 14

JButton

Answer 14

JButton button = new JButton(“Press me”);

Question 15

adding listeners to buttongs

Answer 15

EndingListener buttonEar = newEndingListener());
button.addActionListener(buttonEar);

Question 16

action listener method definition

Answer 16

public void actionPerformed(ActionEvent e)
{
//stuff that gets done
}

Question 17

extending the JFrame

Answer 17

public class windowOne extends JFrame{
    public windowOne(){
         super();

     ///stuff

}
}

create another class for the listeners

Question 18

JLabel

Answer 18

JLabel greeting = new JLabel("Hello");
add(greeting); //if the program is an extension

Question 19

can you colour a JFrame directly

Answer 19

no - must color a content pane of the jframe

• getContentPane().setBackground(Color);
• e.g. Color.BLACK;

Question 20

three main layouts

Answer 20

BorderLayout
FlowLayout - default
GridLayout

Question 21

borderlayout

Answer 21

setLayout(new BorderLayout());
add(label1, BorderLayout.South);

Question 22

flowlayout

Answer 22

setLayout(new FlowLayout()); - arranges compnents one after the other from left to right - order - order of added

Question 23

gridlayout

Answer 23

setLayout(new GridLayout(rows, columns));
added in grid from left to right - top from filled first - positions cannot be skipped

Question 24

Panel

Answer 24

class that serves as a simpler container
JPanel somePanel = new JPanel();

Question 25

the container class

Answer 25

• in awt

- Any class that is a descendent class of the class Container is considered to be a container class

Question 26

the JComponent class

Answer 26

Any JComponentobject or componentcan be added to any container class object

Question 27

the three objects that make up almost every gui using swing container classes

Answer 27

the container
components
layout manager

Question 28

menu

Answer 28

JMenu
- choice menu is called a menu item - object of class JMenuItem

Question 29

menu bar

Answer 29

container for menus 
JMenuBar bar = new JMenuBar();

Question 30

2 different ways to add a menu bar to a JFrame

Answer 30

1 - Using the setJMenuBar method: setJMenuBar(bar);

2 - Using the add method – which can be used to add a menu bar to a JFrame or any other container

Question 31

The classes JButtonand JMenuItemare derived classes of the abstract class named…

Answer 31

AbstractButton

Question 32

what happens when the user clicks a button

Answer 32

• action event becomes an argument to an actionPerformed method
• action event contains a string instance var called the action command for the button or menu item
• default value for this string - the string attached to the button
• This string can be retrieved with the getActionCommand method e.getActionCommand()

Question 33

the setActionCommand

Answer 33

can be used to change the action command for a component - This is especially useful when two or more buttons or menu items have the same default action command strings

Question 34

having listeners as inner classes

Answer 34

public class ListenerOne implements ActionListener{
public void actionPerformed(ActionEvent e){
     //stuffs
}
}

Question 35

textfields

Answer 35

• One line display - used to get one line text input from user
• JTextField name = new JTextField(“Enter name here.”, 30);

Question 36

getText, setText

Answer 36

getText: can read the text in the text field
setText: can be used to display new text string in a txt field

Question 37

textarea

Answer 37

JTextArea textA = new JTextArea(“String”, lines, chars per line);

Question 38

txtarea.setLineWrap(boolean);

Answer 38

to see or not to see characters that exceed the limit

Question 39

txtarea.setEditable(boolean)

Answer 39

only the gui can change this - not the user

Question 40

em space

Answer 40

number of characters that a textfield or area can use is the number of em spaces - space needed for “M”