Java Graphics Quick Reference

Swing/GUI Cheat Sheet

General reminders

To display a Swing component, you must:

Construct and initialize the component.
Example: button = new JButton ("ButtonLabel");
Add it to the content pane of the window or to a JPanel that is added to the display.
Example: getContentPane().add (button);
Import javax.swing.* and sometimes also java.awt.* at the beginning of the class creating the components.

To get events from a GUI component, you must do the following:

Declare that the class handling the event implements the appropriate listener interface.
Example: implements ActionListener
Define the method that the listener interface requires.
Example: public void actionPerformed (ActionEvent event)
Add a listener appropriate for the component to the component.
Example: button.addActionListener (this);
Import java.awt.event.* (and occasionally javax.swing.event.*) at the beginning of the class that is the listener.

When the listener method is called, you can find out which component sent the event by calling getSource() on the event.

    public void actionPerformed (ActionEvent event) {
        Object theButton = event.getSource();
        if (theButton == framedCircleButton) {
            // Create a framed circle
        }
    }

If a method returns a String, remember to compare the result using the equals method, not ==:

    aMenu.getSelectedItem ().equals ("A value")

GUI Components

The following methods can be applied to any Component:

    void setFont (Font f)
    void setForeground (Color c)
    void setBackground (Color c)

To construct a font use:

    new Font (String name, int style, int size)

Style can be one of Font.BOLD, Font.ITALIC, Font.PLAIN, or Font.BOLD + Font.ITALIC.

The specific components we have considered:

JButton

Constructor:

new JButton (String s)

General Methods:

String getText ( )
void setText (String s)

Listener Interface:

ActionListener

Adding the listener:

void addActionListener (ActionListener al)

Listening Method:

void actionPerformed (ActionEvent e)

JComboBox
Constructor and Initialization:
```
new JComboBox ( )
void addItem (Object item)
```
General Methods:
To find out which item was selected, use:
```
Object getSelectedItem ( )
```
If you wish to treat the value returned from this method as a String, you may use either the toString() method, as in
```
String text = menu.getSelectedItem().toString();
```
or a type cast, as in:
```
String text = (String) menu.getSelectedItem ( );
```
To find out the index of the item that was selected, use:
```
int getSelectedIndex ( )
 
```
Listener Interface:
```
ItemListener
```
Adding the listener:
```
void addItemListener (ItemListener il)
```
Listening Method:
```
void itemStateChanged (ItemEvent e)
```
JLabel
Constructors:
```
new JLabel (String s)
```
```
new JLabel (String s, int align)
```
align is one of JLabel.RIGHT, JLabel.LEFT, JLabel.CENTER
General Methods:
```
void setText (String s)
```
```
String getText ( )
```
Listener Interface:

no listeners available for JLabels

JSlider

Constructor:

new JSlider (int orientation, 
              int minimum, int maximum, int initialValue)

orientation is one of JSlider.HORIZONTAL or JSlider.VERTICAL

General Methods:

void setValue (int newVal)

To find out the current value, use:

int getValue ( )

Listener Interface:

ChangeListener

Adding the Listener:

addChangeListener (ChangeListener al)

Listening Method:

void stateChanged (ChangeEvent e)

JTextField

Constructors:

new JTextField (String s)

General Methods:

void setText (String s)

To find out the value typed, use:

String getText ( )

Listener Interface:

ActionListener

Adding the Listener:

addActionListener (ActionListener al)

Listening Method:

void actionPerformed (ActionEvent e)

Containers

Both JPanel and the object obtained by sending getContentPane() to a WindowController object are containers (and have type Container). The following methods are available for all containers.

To define the type of layout, use:

    void setLayout (LayoutManager lm)

LayoutManager may be any of the layout managers listed below.

To add something to a container:

    void add (Component c)

Component may be any Component (such as JButton, JTextField, JSlider, ...) or Container (such as JPanel). Use the method above if the container has a FlowLayout or GridLayout. Use the one below if it has a BorderLayout.

    void add (Component c, int position)

The position may be any of BorderLayout.NORTH, BorderLayout.SOUTH, BorderLayout.EAST,
BorderLayout.WEST, or BorderLayout.CENTER.

Constructing a JPanel is very straightforward:

new JPanel ()

Layout Managers

BorderLayout (Default for WindowController)
Constructor:
```
new BorderLayout ()
```
FlowLayout (Default for JPanel)
Constructor:
```
new FlowLayout ()
```

GridLayout

Constructors:

new GridLayout (int rows, int cols)

new GridLayout (int rows, int cols, int colSpacing, int rowSpacing)