Components Jan 14 2019 Types of Components Button Canvas Checkbox Choice Label List Scrollbar TextComponent TextArea TextField 2 Button new Button constructs a Button with no text new Button String constructs a Button with the specified text void addActionListener ActionListener void removeActionListener ActionListener String getLabel void setLabel String String actionEvent getActionCommand Returns the action command associated with this Button By default the action command the text on the Button 3 A Button listener button addActionListener new MyButtonListener class MyButtonListener implements ActionListener public void actionPerformed ActionEvent event showStatus Button clicked 4 Label constructors new Label constructs a Label with no text new Label String constructs a Label with the specified text new Label String alignment constructs a label with the specified text and alignment Label LEFT Label RIGHT Label CENTER These are int constants defined in the Label class 5 Label methods String getText void setText String int getAlignment void setAlignment int 6 Scrollbar constructors new Scrollbar creates a vertical Scrollbar new Scrollbar int orientation Scrollbar HORIZONTAL or Scrollbar VERTICAL new 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 7 Scrollbars bubbleSize minimum The units for bubbleSize are the same as those for minimum and maximum maximum maximum bubbleSize The scrollbar reading is taken from the left edge of the bubble 8 Scrollbar methods void addAdjustmentListener AdjustmentListener void removeAdjustmentListener AdjustmentListener int getMinimum void setMinimum int int getMaximum void setMaximum int int getValue void setValue int 9 A Scrollbar listener scrollbar addAdjustmentListener new MyScrollbarListener class MyScrollbarListener implements AdjustmentListener public void adjustmentValueChanged AdjustmentEvent event showStatus Scrollbar scrollbar getValue 10 Checkbox constructors new new new new new Checkbox Checkbox String Checkbox String boolean Checkbox String boolean CheckboxGroup Checkbox String CheckboxGroup boolean 11 Checkbox methods void addItemListener ItemListener void removeItemListener ItemListener CheckboxGroup getCheckboxGroup void setCheckboxGroup CheckboxGroup String getLabel void setLabel String 12 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 13 CheckboxGroup methods Checkbox getSelectedCheckbox Suggested use myCG getSelectedCheckbox getLabel void setSelectedCheckbox Checkbox 14 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 15 Choice constructor new Choice After constructing a Choice use add String to add items to it 16 Choice methods addItemListener ItemListener removeItemListener ItemListener void add String void remove String void removeAll String getSelectedItem void select String 17 A Choice listener choice addItemListener new MyChoiceListener class MyChoiceListener implements ItemListener public void itemStateChanged ItemEvent event showStatus Choice choice getSelectedItem 18 List constructors new List constructs an empty list new List int int the number of items visible a scrollbar is automatically added if needed new List int boolean boolean true if multiple selection is allowed 19 List methods I void addItemListener ItemListener void removeItemListener ItemListener void add String void remove String void removeAll 20 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 21 A List listener list addItemListener new MyListListener class MyListListener implements ItemListener public void itemStateChanged ItemEvent event showStatus List list getSelectedItem 22 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 23 TextField constructors new TextField new TextField int new TextField String int the approximate desired number of columns String the initial text in the TextField new TextField String int 24 TextField methods void addActionListener ActionListener void removeActionListener ActionListener The ActionListener for a TextField responds only when the Enter key is pressed 25 TextArea constructors new TextArea new TextArea int rows int columns new TextArea int rows int columns int scroll TextArea SCROLLBARS VERTICAL ONLY TextArea SCROLLBARS HORIZONTAL ONLY TextArea SCROLLBARS BOTH TextArea SCROLLBARS NONE new TextArea String new TextArea String int rows int columns 26 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 27 Suggestion Don t use text listeners Text fields are intended to be passive that is nothing should happen immediately as a result of typing into them Consequently I ve seen a lot of programs in which text listeners do their work at the wrong time It usually works much better to ignore text fields until an active control such as a Button is used and then do getText to find the current value in the text field 28 Canvas This is a rectangular blank area that you can paint on Constructor new Canvas Don t use Canvas directly instead subclass it and override its void paint Graphics method Or even simpler Paint directly on a Panel 29 The End 30
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