Lecture 6 - Swing

Question 1

What are 5 examples of JFrame methods?

Answer 1

setTitle(String)
setSize(int dimx, int dimy) - num of pixels in the x and y directions
setLocation(int x, int y) - distance of top left corner of frame from top left corner of monitor, in pixels. If you don’t include any location method, the location is automatically set to (0,0).
setVisible(boolean)
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE)- ensure the system exits the application when user closed the Frame

Question 2

How do we create a GUI in Java swing?

Answer 2

1. The program creates a window object (JFrame)
2. The program creates several component objects (JComponents)
3. Layout managers (allows children to overlap)
4. Event listener objects (handles the events that arrive at each of the components).

Question 3

How do we customise our own JFrame?

Answer 3

use inheritence ie. extends JFrame

Question 4

What class do we have to import to use JFrame?

Answer 4

javax.swing.JFrame

Question 5

What are 3 examples of layout managers?

Answer 5

1. FlowLayout (horizontal)
2. BorderLayout (content pane is divided into 5 areas)
3. GridLayout(centres vertically & horizontally)

Question 6

Give an example of how you could create a panel & give it a GridLayout?

Answer 6

JPanel myPanel = new JPanel( new GridLayout(0,1))

There are actually 2 rows 1 col, but we can add 0 because the computer will interpret it as “use however many rows are needed”.

Question 7

Give an example of how you could create a panel and give it a FlowLayout

Answer 7

JPanel mainPanel = new JPanel(FlowLayout())

**don’t need this because FlowLayout is the deafult layout for a JPanel

Question 8

Give an example of how you create a label and add it to a panel?

Answer 8

Global:
private JLabel label1;

Main:
label1 = new JLabel(“Click here”);
JPanel myPanel = new JPanel();
myPanel.add(label1);

Question 9

Give an example of how you can create a text field and add it to a panel

Answer 9

Global:
private JTextField textField1;

Main:
textField1  = new JTextField("initial text", 15);

JPanel p = new JPanel();
p.add(textField1);

Question 10

Give an example of how you can add a button?

Answer 10

Global:
private JButton button1;

Main:
button1  = new JButton("quit");

JPanel myPanel = new JPanel();

myPanel.add(button1);

Question 11

Give an example of how to add a label with the BorderLayout() to a panel

Answer 11

this.add(new JLabel("NORTH"), BorderLayout.NORTH);
or
p.add(new JLabel("bottom"), BorderLayout.SOUTH);

Question 12

Explain a JPanel

Answer 12

Its a generic container

Its 1 component, but can store multiple components

Question 13

What is the default layout for JPanel?

Answer 13

FlowLayout();

Question 14

What is the default layout for JFrame?

Answer 14

BorderLayout();

Question 15

What are useful methods for JPanel?

Answer 15

setBackground(color)
getHeight()
getWidth()

Question 16

Why is BorderLayout() useful?

Answer 16

• Its like a container that lets us arrange and resize components to fit in 5 regions: north, south, east, west, center.
• there can be 1 component per region:NORTH, SOUTH, EAST, WEST, CENTER

** note american spelling needed

Question 17

Why do we have to layer things on top of each other to build a GUI?

Answer 17

Because we are limited in what we can do in 1 go.

Question 18

How do you set a constant for width and height?

Answer 18

Add a global constant:

final int WIDTH = 200;
final int HEIGHT = 100;

// use capitals because we are referring to a constant

Question 19

What does this mean:

public class a extends JFrame{
final int UNIT = 20;
this.setSize(30*UNIT, 30*UNIT)

Answer 19

It says that UNIT is a constant int 20. This is the size of 1 mini box.

To get the size of the large box. We need to multiply the rows and columns by 30 because there are 30 mini boxes.

Question 20

What would this look like?

import java.awt.*;
 import java.applet.Applet;
 public class ButtonGrid extends Applet {
     public void init() {
         setLayout(new GridLayout(3,2));
         add(new Button("1"));
         add(new Button("2"));
         add(new Button("3"));
         add(new Button("4"));
         add(new Button("5"));
         add(new Button("6"));
     }
 }

Answer 20

Depends on the ComponentOrientation!

This 1 is left to right so it would look like this:

1 2
3 4
5 6

Question 21

How do you create a border?

Answer 21

// adding borders 
		Border blackline = BorderFactory.createLineBorder(Color.black);

		topPanel.setBorder(blackline);
		bottomPanel.setBorder(blackline);
		rightPanel.setBorder(blackline);
		leftPanel.setBorder(blackline);
		centerPanel.setBorder(blackline);

Question 22

What is GridBagLayout?

Answer 22

Is a flexible layout manager that aligns the components vertically and horizontally without requiring that the components be of the same size.

This is different to gridlayout which requires the rectangles to be divided into equal sizes.

Question 23

How do you set font and change the font of the label?

Answer 23

Font f = new Font(“TimesRoman”, Font.PLAIN, 24);

// changing the font of the labels
topPanel.setFont(f);