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Components
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Types of Components Button Canvas Checkbox Choice Label List Scrollbar TextComponent –TextArea –TextField
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Button Button() constructs a Button with no text Button(String) constructs a Button with the specified text void addActionListener(ActionListener) void removeActionListener(ActionListener) String getLabel() void setLabel(String) String actionEvent.getActionCommand()
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A Button listener button.addActionListener (new MyButtonListener ()); class MyButtonListener implements ActionListener { public void actionPerformed (ActionEvent event) { showStatus ("Button clicked."); } }
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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
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Label methods String getText() void setText(String) int getAlignment() void setAlignment(int)
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Scrollbar constructors Scrollbar() creates a vertical Scrollbar Scrollbar(int orientation) –Scrollbar.HORIZONTAL or Scrollbar.VERTICAL Scrollbar(int orientation, int initialValue, int bubbleSize, int minimum, int maximum) –bubbleSize : size of the bubble (sometimes called elevator) –min value of Scrollbar = minimum –max value of Scrollbar = maximum - bubbleSize ( value of scrollbar is given by left or top edge of bubble) –initialValue : the initial position setting of the bubble
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Scrollbars bubbleSize minimum maximum maximum — bubbleSize The units for bubbleSize are the same as those for minimum and maximum
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Scrollbar methods void addAdjustmentListener(AdjustmentListener) void removeAdjustmentListener(AdjustmentListener) int getMinimum() void setMinimum(int) int getMaximum() void setMaximum(int) int getValue() void setValue(int)
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A Scrollbar listener scrollbar.addAdjustmentListener(new MyScrollbarListener ()); class MyScrollbarListener implements AdjustmentListener { public void adjustmentValueChanged (AdjustmentEvent event) { showStatus ("Scrollbar: " + scrollbar.getValue ()); } };
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Checkbox constructors Checkbox() Checkbox(String) Checkbox(String, boolean) Checkbox(String, boolean, CheckboxGroup) Checkbox(String, CheckboxGroup, boolean)
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Checkbox methods void addItemListener(ItemListener) void removeItemListener(ItemListener) CheckboxGroup getCheckboxGroup() void setCheckboxGroup(CheckboxGroup) String getLabel() void setLabel(String)
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A Checkbox listener checkbox.addItemListener (new MyCheckboxListener ()); class MyCheckboxListener implements ItemListener { public void itemStateChanged (ItemEvent event) { showStatus ("Checkbox status is now " + (event.getStateChange () == ItemEvent.SELECTED)); } };
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CheckboxGroup methods Checkbox getSelectedCheckbox() –Suggested use: myCG.getSelectedCheckbox().getLabel() void setSelectedCheckbox(Checkbox)
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A CheckboxGroup listener No such thing—listen to individual Checkboxes checkbox1.addItemListener (myCheckboxGroupListener); checkbox2.addItemListener (myCheckboxGroupListener); class MyCheckboxGroupListener implements ItemListener { public void itemStateChanged (ItemEvent event) { Checkbox d = checkboxGroup.getSelectedCheckbox (); showStatus ("CheckboxGroup: " + d.getLabel ()); } }
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Choice constructor Choice() After constructing a Choice, use add(String) to add items to it
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Choice methods addItemListener(ItemListener) removeItemListener(ItemListener) void add (String) void remove(String) void removeAll() String getSelectedItem() void select(String)
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A Choice listener choice.addItemListener (new MyChoiceListener ()); class MyChoiceListener implements ItemListener { public void itemStateChanged (ItemEvent event) { showStatus ("Choice: " + choice.getSelectedItem ()); } };
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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
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List methods I void addItemListener(ItemListener) void removeItemListener(ItemListener) void add(String) void remove(String) void removeAll()
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List methods II String getSelectedItem() String[] getSelectedItems() int getSelectedIndex() int[] getSelectedIndexes() void select(int) // can only select by index –There are other methods for adding, removing, etc. by index
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A List listener list.addItemListener (new MyListListener ()); class MyListListener implements ItemListener { public void itemStateChanged (ItemEvent event) { showStatus ("List: " + list.getSelectedItem ()); } };
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TextComponent No constructors –Instead, construct a TextField or TextArea void addTextListener(TextListener) void removeTextListener(TextListener) String getText() void setText(String) boolean isEditable() void setEditable(boolean)
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TextField constructors TextField() TextField(int) –int : the approximate desired number of columns TextField(String) –String : the initial text in the TextField TextField(String, int)
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TextField methods void addActionListener(ActionListener) void removeActionListener(ActionListener ) The ActionListener for a TextField responds only when the Enter key is pressed
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TextArea constructors TextArea() TextArea(int rows, int columns) TextArea(int rows, int columns, int scroll) –TextArea.SCROLLBARS_VERTICAL_ONLY –TextArea.SCROLLBARS_HORIZONTAL_ONLY –TextArea.SCROLLBARS_BOTH –TextArea.SCROLLBARS_NONE TextArea(String) TextArea(String, int rows, int columns)
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TextComponent listeners textField.addActionListener (new MyTextFieldListeners ()); textField.addTextListener (new MyTextFieldListeners ()); class MyTextFieldListeners implements ActionListener,TextListener { public void actionPerformed (ActionEvent event) { showStatus ("TextField (ActionListener): " + textField.getText ()); } public void textValueChanged (TextEvent event) { showStatus ("TextField (TextListener): " + textField.getText ()); } };
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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
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The End
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