Components Types of Components Button Canvas Checkbox Choice

Components

Types of Components • • • Button Canvas Checkbox Choice Label • List • Scrollbar • Text. Component – Text. Area – Text. Field

Button • Button() constructs a Button with no text • Button(String) constructs a Button with the specified text • void add. Action. Listener(Action. Listener) • void remove. Action. Listener(Action. Listener) • String get. Label() • void set. Label(String) • String action. Event. get. Action. Command()

A Button listener button. add. Action. Listener (new My. Button. Listener ()); class My. Button. Listener implements Action. Listener { public void action. Performed (Action. Event event) { show. Status ("Button clicked. "); } }

Label constructors • Label() constructs a Label with no text • Label(String) constructs a Label with the specified text • Label(String, int) constructs a label with the specified text and alignment: – Label. LEFT – Label. RIGHT – Label. CENTER

Label methods • • String get. Text() void set. Text(String) int get. Alignment() void set. Alignment(int)

Scrollbar constructors • Scrollbar() creates a vertical Scrollbar • Scrollbar(int orientation) – Scrollbar. HORIZONTAL or Scrollbar. VERTICAL • Scrollbar(int orientation, int initial. Value, int bubble. Size, int minimum, int maximum) – bubble. Size: size of the bubble (sometimes called elevator) – min value of Scrollbar = minimum – max value of Scrollbar = maximum - bubble. Size • (value of scrollbar is given by left or top edge of bubble) – initial. Value: the initial position setting of the bubble

Scrollbars bubble. Size minimum The units for bubble. Size are the same as those for minimum and maximum — bubble. Size

Scrollbar methods • void add. Adjustment. Listener(Adjustment. Listener) • void remove. Adjustment. Listener(Adjustment. Listener) • int get. Minimum() • void set. Minimum(int) • int get. Maximum() • void set. Maximum(int) • int get. Value() • void set. Value(int)

A Scrollbar listener scrollbar. add. Adjustment. Listener(new My. Scrollbar. Listener ()); class My. Scrollbar. Listener implements Adjustment. Listener { public void adjustment. Value. Changed (Adjustment. Event event) { show. Status ("Scrollbar: " + scrollbar. get. Value ()); } };

Checkbox constructors • • • Checkbox() Checkbox(String, boolean) Checkbox(String, boolean, Checkbox. Group) Checkbox(String, Checkbox. Group, boolean)

Checkbox methods • void add. Item. Listener(Item. Listener) • void remove. Item. Listener(Item. Listener) • Checkbox. Group get. Checkbox. Group() • void set. Checkbox. Group(Checkbox. Group) • String get. Label() • void set. Label(String)

A Checkbox listener checkbox. add. Item. Listener (new My. Checkbox. Listener ()); class My. Checkbox. Listener implements Item. Listener { public void item. State. Changed (Item. Event event) { show. Status ("Checkbox status is now " + (event. get. State. Change () == Item. Event. SELECTED)); } };

Checkbox. Group methods • Checkbox get. Selected. Checkbox() – Suggested use: my. CG. get. Selected. Checkbox(). get. Label() • void set. Selected. Checkbox(Checkbox)

A Checkbox. Group listener • No such thing—listen to individual Checkboxes checkbox 1. add. Item. Listener (my. Checkbox. Group. Listener); checkbox 2. add. Item. Listener (my. Checkbox. Group. Listener); class My. Checkbox. Group. Listener implements Item. Listener { public void item. State. Changed (Item. Event event) { Checkbox d = checkbox. Group. get. Selected. Checkbox (); show. Status ("Checkbox. Group: " + d. get. Label ()); } }

Choice constructor • Choice() • After constructing a Choice, use add(String) to add items to it

Choice methods • add. Item. Listener(Item. Listener) • remove. Item. Listener(Item. Listener) • void add (String) • void remove. All() • String get. Selected. Item() • void select(String)

A Choice listener choice. add. Item. Listener (new My. Choice. Listener ()); class My. Choice. Listener implements Item. Listener { public void item. State. Changed (Item. Event event) { show. Status ("Choice: " + choice. get. Selected. Item ()); } };

List constructors • List() constructs an empty list • List(int) – int: the number of items visible (a scrollbar is automatically added if needed) • List(int, boolean) – boolean: true if multiple selection is allowed

List methods I • void add. Item. Listener(Item. Listener) • void remove. Item. Listener(Item. Listener) • void add(String) • void remove. All()

List methods II • String get. Selected. Item() • String[] get. Selected. Items() • int get. Selected. Index() • int[] get. Selected. Indexes() • void select(int) // can only select by index – There are other methods for adding, removing, etc. by index

A List listener list. add. Item. Listener (new My. Listener ()); class My. Listener implements Item. Listener { public void item. State. Changed (Item. Event event) { show. Status ("List: " + list. get. Selected. Item ()); } };

Text. Component • No constructors – Instead, construct a Text. Field or Text. Area • void add. Text. Listener(Text. Listener) • void remove. Text. Listener(Text. Listener) • String get. Text() • void set. Text(String) • boolean is. Editable() • void set. Editable(boolean)

Text. Field constructors • Text. Field() • Text. Field(int) – int: the approximate desired number of columns • Text. Field(String) – String: the initial text in the Text. Field • Text. Field(String, int)

Text. Field methods • void add. Action. Listener(Action. Listener) • void remove. Action. Listener(Action. Listener) • The Action. Listener for a Text. Field responds only when the Enter key is pressed

Text. Area constructors • Text. Area() • Text. Area(int rows, int columns, int scroll) – – Text. Area. SCROLLBARS_VERTICAL_ONLY Text. Area. SCROLLBARS_HORIZONTAL_ONLY Text. Area. SCROLLBARS_BOTH Text. Area. SCROLLBARS_NONE • Text. Area(String) • Text. Area(String, int rows, int columns)

Text. Component listeners text. Field. add. Action. Listener (new My. Text. Field. Listeners ()); text. Field. add. Text. Listener (new My. Text. Field. Listeners ()); class My. Text. Field. Listeners implements Action. Listener, Text. Listener { public void action. Performed (Action. Event event) { show. Status ("Text. Field (Action. Listener): " + text. Field. get. Text ()); } public void text. Value. Changed (Text. Event event) { show. Status ("Text. Field (Text. Listener): " + text. Field. get. Text ()); } };

Canvas • This is a rectangular blank area that you can paint on • Constructor: Canvas() • Don't use Canvas directly; instead, subclass it and override its void paint(Graphics) method

The End