Kĩ thuật lập trình - Gui components: Part 1

11GUI Components: Part 11 Do you think I can listen all day to such stuff?Lewis CarrollEven a minor event in the life of a child is an event of that child’s world and thus a world event.Gaston BachelardYou pays your money and you takes your choice.PunchGuess if you can, choose if you dare.Pierre Corneille2OBJECTIVESIn this chapter you will learn: The design principles of graphical user interfaces (GUIs).To build GUIs and handle events generated by user interactions with GUIs.To understand the packages containing GUI components, event-handling classes and interfaces.To create and manipulate buttons, labels, lists, text fields and panels.To handle mouse events and keyboard events.To use layout managers to arrange GUI components311.1 Introduction 11.2 Simple GUI-Based Input/Output with JOptionPane 11.3 Overview of Swing Components 11.4 Displaying Text and Images in a Window 11.5 Text Fields and an Introduction to Event Handling with Nested Classes 11.6 Common GUI Event Types and Listener Interfaces 11.7 How Event Handling Works 11.8 JButton 11.9 Buttons That Maintain State 11.9.1 JCheckBox 11.9.2 JRadioButton11.10 JComboBox and Using an Anonymous Inner Class for Event Handling 411.11 JList 11.12 Multiple-Selection Lists 11.13 Mouse Event Handling 11.14 Adapter Classes 11.15 JPanel Sublcass for Drawing with the Mouse 11.16 Key-Event Handling 11.17 Layout Managers 11.17.1 FlowLayout 11.17.2 BorderLayout 11.17.3 GridLayout 11.18 Using Panels to Manage More Complex Layouts 11.19 JTextArea 11.20 Wrap-Up 511.1 IntroductionGraphical user interface (GUI)Presents a user-friendly mechanism for interacting with an applicationOften contains title bar, menu bar containing menus, buttons and combo boxesBuilt from GUI components6Look-and-Feel Observation 11.1Consistent user interfaces enable a user to learn new applications faster. 7Fig. 11.1 | Internet Explorer window with GUI components. buttonmenustitle barmenu barcombo boxscrollbars811.2 Simple GUI-Based Input/Output with JOptionPaneDialog boxesUsed by applications to interact with the userProvided by Java’s JOptionPane classContains input dialogs and message dialogs9OutlineAddition.java(1 of 2)Show input dialog to receive first integerShow input dialog to receive second integerShow message dialog to output sum to user10OutlineAddition.java(2 of 2)Input dialog displayed by lines 10–11Input dialog displayed by lines 12–13Message dialog displayed by lines 22–23Text field in which the user types avaluePrompt to the userWhen the user clicks OK, showInputDialog returns to the program the 100 typed by the user as a String. The program must convert the String to an inttitle barWhen the user clicks OK, the message dialog is dismissed (removed from the screen)11Look-and-Feel Observation 11.2The prompt in an input dialog typically uses sentence-style capitalization—a style that capitalizes only the first letter of the first word in the text unless the word is a proper noun (for example, Deitel). 12Look-and-Feel Observation 11.3The title bar of a window typically uses book-title capitalization—a style that capitalizes the first letter of each significant word in the text and does not end with any punctuation (for example, Capitalization in a Book Title). 13Fig. 11.3 | JOptionPane static constants for message dialogs. 1411.3 Overview of Swing ComponentsSwing GUI componentsDeclared in package javax.swingMost are pure Java componentsPart of the Java Foundation Classes (JFC)15Fig. 11.4 | Some basic GUI components. 16Swing vs. AWTAbstract Window Toolkit (AWT)Precursor to SwingDeclared in package java.awtDoes not provide consistent, cross-platform look-and-feel17Portability Tip 11.1 Swing components are implemented in Java, so they are more portable and flexible than the original Java GUI components from package java.awt, which were based on the GUI components of the underlying platform. For this reason, Swing GUI components are generally preferred. 18Lightweight vs. Heavyweight GUI ComponentsLightweight componentsNot tied directly to GUI components supported by underlying platformHeavyweight componentsTied directly to the local platformAWT componentsSome Swing components19Look-and-Feel Observation 11.4 The look and feel of a GUI defined with heavyweight GUI components from package java.awt may vary across platforms. Because heavyweight components are tied to the local-platform GUI, the look and feel varies from platform to platform. 20Superclasses of Swing’s Lightweight GUI ComponentsClass Component (package java.awt)Subclass of ObjectDeclares many behaviors and attributes common to GUI componentsClass Container (package java.awt)Subclass of ComponentOrganizes ComponentsClass JComponent (package javax.swing)Subclass of ContainerSuperclass of all lightweight Swing components21Software Engineering Observation 11.1 Study the attributes and behaviors of the classes in the class hierarchy of Fig. 11.5. These classes declare the features that are common to most Swing components. 22Fig. 11.5 | Common superclasses of many of the Swing components. 23Superclasses of Swing’s Lightweight GUI ComponentsCommon lightweight component featuresPluggable look-and-feel to customize the appearance of componentsShortcut keys (called mnemonics)Common event-handling capabilitiesBrief description of component’s purpose (called tool tips)Support for localization2411.4 Displaying Text and Images in a WindowClass JFrameMost windows are an instance or subclass of this classProvides title barProvides buttons to minimize, maximize and close the application25Labeling GUI ComponentsLabelText instructions or information stating the purpose of each componentCreated with class JLabel26Look-and-Feel Observation 11.5 Text in a JLabel normally uses sentence-style capitalization. 27Specifying the LayoutLaying out containersDetermines where components are placed in the containerDone in Java with layout managersOne of which is class FlowLayoutSet with the setLayout method of class JFrame28OutlineLabelFrame.java(1 of 2)29OutlineLabelFrame.java(2 of 2)30OutlineLabelTest.java31Creating and Attaching label1Method setToolTipText of class JComponentSpecifies the tool tipMethod add of class ContainerAdds a component to a container32Common Programming Error 11.1 If you do not explicitly add a GUI component to a container, the GUI component will not be displayed when the container appears on the screen. 33Look-and-Feel Observation 11.6 Use tool tips to add descriptive text to your GUI components. This text helps the user determine the GUI component’s purpose in the user interface. 34Creating and Attaching label2 Interface IconCan be added to a JLabel with the setIcon methodImplemented by class ImageIconInterface SwingConstantsDeclares a set of common integer constants such as those used to set the alignment of componentsCan be used with methods setHorizontalAlignment and setVerticalAlignment35Creating and Attaching label3 Other JLabel methodsgetText and setTextFor setting and retrieving the text of a labelgetIcon and setIconFor setting and retrieving the icon displayed in the labelgetHorizontalTextPosition and setHorizontalTextPositionFor setting and retrieving the horizontal position of the text displayed in the label36Fig. 11.8 | Some basic GUI components. 37Creating and Displaying a LabelFrame Window Other JFrame methodssetDefaultCloseOperationDictates how the application reacts when the user clicks the close buttonsetSizeSpecifies the width and height of the windowsetVisibleDetermines whether the window is displayed (true) or not (false)3811.5 Text Fields and an Introduction to Event Handling with Nested ClassesGUIs are event-drivenA user interaction creates an eventCommon events are clicking a button, typing in a text field, selecting an item from a menu, closing and window and moving the mouseThe event causes a call to a method called an event handler3911.5 Text Fields and an Introduction to Event Handling with Nested ClassesClass JTextComponentSuperclass of JTextFieldSuperclass of JPasswordFieldAdds echo character to hide text input in componentAllows user to enter text in the component when component has the application’s focus40OutlineTextFieldFrame.java(1 of 3)Create a new JTextField41OutlineTextFieldFrame.java (2 of 3)Create a new JTextFieldMake this JTextField uneditableCreate a new JPasswordFieldCreate event handlerRegister event handlerCreate event handler class by implementing the ActionListener interfaceDeclare actionPerformed method42OutlineTextFieldFrame.java(3 of 3)Test if the source of the event is the first text fieldGet text from text fieldGet text from text fieldGet text from text fieldGet password from password fieldTest if the source of the event is the second text fieldTest if the source of the event is the third text fieldTest if the source of the event is the password field43OutlineTextFieldTest.java(1 of 2)44OutlineTextFieldTest.java(2 of 2)45Steps Required to Set Up Event Handling for a GUI ComponentSeveral coding steps are required for an application to respond to eventsCreate a class for the event handlerImplement an appropriate event-listener interfaceRegister the event handler46Using a Nested Class to Implement an Event HandlerTop-level classesNot declared within another classNested classesDeclared within another classNon-static nested classes are called inner classesFrequently used for event handling47Software Engineering Observation 11.2 An inner class is allowed to directly access its top-level class’s variables and methods, even if they are private. 48Using a Nested Class to Implement an Event HandlerJTextFields and JPasswordFieldsPressing enter within either of these fields causes an ActionEventProcessed by objects that implement the ActionListener interface49Registering the Event Handler for Each Text FieldRegistering an event handlerCall method addActionListener to register an ActionListener objectActionListener listens for events on the object50Software Engineering Observation 11.3The event listener for an event must implement the appropriate event-listener interface. 51Common Programming Error 11.2Forgetting to register an event-handler object for a particular GUI component’s event type causes events of that type to be ignored. 52Details of Class TextFieldHandler’s actionPerformed MethodEvent sourceComponent from which event originatesCan be determined using method getSourceText from a JTextField can be acquired using getActionCommandText from a JPasswordField can be acquired using getPassword5311.6 Common GUI Event Types and Listener InterfacesEvent typesAll are subclasses of AWTEventSome declared in package java.awt.eventThose specific to Swing components declared in javax.swing.event5411.6 Common GUI Event Types and Listener InterfacesDelegation event modelEvent source is the component with which user interactsEvent object is created and contains information about the event that happenedEvent listener is notified when an event happens55Fig. 11.11 | Some event classes of package java.awt.event. 56Fig. 11.12 | Some common event-listener interfaces of package java.awt.event. 5711.7 How Event Handling WorksRemaining questionsHow did the event handler get registered?How does the GUI component know to call actionPerformed rather than some other event-handling method?58Registering EventsEvery JComponent has instance variable listenerListObject of type EventListenerListMaintains references to all its registered listeners59Fig. 11.13 | Event registration for JTextField textField1 . 60Event-Handler InvocationEvents are dispatched to only the event listeners that match the event typeEvents have a unique event ID specifying the event typeMouseEvents are handled by MouseListeners and MouseMotionsListenersKeyEvents are handled by KeyListeners6111.8 JButtonButtonComponent user clicks to trigger a specific actionCan be command button, check box, toggle button or radio buttonButton types are subclasses of class AbstractButton62Look-and-Feel Observation 11.7 Buttons typically use book-title capitalization. 6311.8 JButtonCommand buttonGenerates an ActionEvent when it is clickedCreated with class JButtonText on the face of the button is called button label64Look-and-Feel Observation 11.8 Having more than one JButton with the same label makes the JButtons ambiguous to the user. Provide a unique label for each button. 65Fig. 11.14 | Swing button hierarchy. 66OutlineButtonFrame.java(1 of 2)Declare two JButton instance variablesCreate new JButtonCreate two ImageIconsCreate new JButtonSet rollover icon for JButton67OutlineButtonFrame.java(2 of 2)Create handler for buttonsRegister event handlersInner class implements ActionListenerAccess outer class’s instance using this referenceGet text of JButton pressed68OutlineButtonTest.java(1 of 2)69OutlineButtonTest.java(2 of 2)7011.8 JButtonJButtons can have a rollover iconAppears when mouse is positioned over a buttonAdded to a JButton with method setRolloverIcon71Look-and-Feel Observation 11.9  Because class AbstractButton supports displaying text and images on a button, all subclasses of AbstractButton also support displaying text and images. 72Look-and-Feel Observation 11.10 Using rollover icons for JButtons provides users with visual feedback indicating that when they click the mouse while the cursor is positioned over the button, an action will occur. 73Software Engineering Observation 11.4When used in an inner class, keyword this refers to the current inner-class object being manipulated. An inner-class method can use its outer-class object’s this by preceding this with the outer-class name and a dot, as in ButtonFrame.this. 7411.9 Buttons That Maintain StateState buttonsSwing contains three types of state buttonsJToggleButton, JCheckBox and JRadioButtonJCheckBox and JRadioButton are subclasses of JToggleButton7511.9.1 JCheckBoxJCheckBoxContains a check box label that appears to right of check box by defaultGenerates an ItemEvent when it is clickedItemEvents are handled by an ItemListenerPassed to method itemStateChangedMethod isSelected returns whether check box is selected (true) or not (false)76OutlineCheckBoxFrame.java(1 of 3)Declare two JCheckBox instance variablesSet font of text field77OutlineCheckBoxFrame.java(2 of 3)Create two JCheckBoxesCreate event handlerRegister event handler with JCheckBoxesInner class implements ItemListeneritemStateChanged method is called when a JCheckBox is clickedTest whether JCheckBox is selected78OutlineCheckBoxFrame.java(3 of 3)Test source of the eventisSelected method returns whether JCheckBox is selected79OutlineCheckBoxTest.java8011.9.2 JRadioButtonJRadioButtonHas two states – selected and unselectedNormally appear in a group in which only one radio button can be selected at onceGroup maintained by a ButtonGroup objectDeclares method add to add a JRadioButton to groupUsually represents mutually exclusive options81Common Programming Error 11.3 Adding a ButtonGroup object (or an object of any other class that does not derive from Component) to a container results in a compilation error. 82OutlineRadioButtonFrame.java(1 of 3)Declare four JRadioButtons and a ButtonGroup to manage them83OutlineRadioButtonFrame.java(2 of 3)Create the four JRadioButtonsCreate the ButtonGroupAdd each JRadioButton to the ButtonGroup84OutlineRadioButtonFrame.java(3 of 3)Register an event handler with each JRadioButtonEvent handler inner class implements ItemListenerWhen radio button is selected, the text field’s font will be set to the value passed to the constructor85OutlineRadioButtonTest.java8611.10 JComboBox and Using an Anonymous Inner Class for Event HandlingCombo boxAlso called a drop-down listImplemented by class JComboBoxEach item in the list has an indexsetMaximumRowCount sets the maximum number of rows shown at onceJComboBox provides a scrollbar and up and down arrows to traverse list87Look-and-Feel Observation 11.11 Set the maximum row count for a JComboBox to a number of rows that prevents the list from expanding outside the bounds of the window in which it is used. This configuration will ensure that the list displays correctly when it is expanded by the user. 88Using an Anonymous Inner Class for Event HandlingAnonymous inner classSpecial form of inner classDeclared without a nameTypically appears inside a method callHas limited access to local variables89OutlineComboBoxFrame.java(1 of 2)Declare JComboBox instance variable90OutlineComboBoxrame.java(2 of 2)Create JComboBox and set maximum row countCreate anonymous inner class as the event handlerDeclare method itemStateChangedMethod getSelectedIndex locates selected itemTest state change of JComboBox91OutlineComboBoxTest.javaScrollbar to scroll through the items in the listscroll arrowsscroll box92Software Engineering Observation 11.5 An anonymous inner class declared in a method can access the instance variables and methods of the top-level class object that declared it, as well as the method’s final local variables, but cannot access the method’s non-final variables. 93Software Engineering Observation 11.6Like any other class, when an anonymous inner class implements an interface, the class must implement every method in the interface.9411.11 JListListDisplays a series of items from which the user may select one or more itemsImplemented by class JListAllows for single-selection lists or multiple-selection listsA ListSelectionEvent occurs when an item is selectedHandled by a ListSelectionListener and passed to method valueChanged95OutlineListFrame.java(1 of 2)Declare JList instance variable96OutlineListFrame.java(2 of 2)Create JListSet selection mode of JListAdd JList to ScrollPane and add to applicationGet index of selected item97OutlineListTest.java9811.12 Multiple-Selection ListsMultiple-selection listEnables users to select many itemsSingle interval selection allows only a continuous range of itemsMultiple interval selection allows any set of elements to be selected99OutlineMultipleSelectionFrame.java(1 of 3)100OutlineMultipleSelectionFrame.java(2 of 3)Use a multiple interval selection listUse methods setListData and getSelectedValues to copy values from one JList to the other101OutlineMultipleSelectionFrame.java(3 of 3)Set cell width for presentationSet cell height for presentationSet selection model to single interval selection102OutlineMultipleSelectionTest.java10311.13 Mouse Event HandlingMouse eventsCreate a MouseEvent objectHandled by MouseListeners and MouseMotionListeners MouseInputListener combines the two interfacesInterface MouseWheelListener declares method mouseWheelMoved to handle MouseWheelEvents104Fig. 11.27 | MouseListener and MouseMotionListener interface methods. (Part 1 of 2.)105Fig. 11.27 | MouseListener and MouseMotionListener interface methods. (Part 2 of 2.)106Look-and-Feel Observation 11.12 Method calls to mouseDragged and mouseReleased are sent to the MouseMotionListener for the Component on which a mouse drag operation started. Similarly, the mouseReleased method call at the end of a drag operation is sent to the MouseListener for the Component on which the drag operation started. 107OutlineMouseTrackerFrame.java(1 of 4)Create JPanel to capture mouse eventsSet background to whiteCreate JLabel and add to application108OutlineMouseTrackerFrame.java(2 of 4)Create event handler for mouse eventsRegister event handlerImplement mouse listener interfacesFind location of mouse clickDeclare mouseClicked methodDeclare mousePressed methodDeclare mouseReleased method109OutlineMouseTrackerFrame.java(3 of 4)Declare mouseEntered methodSet background of JPanelDeclare mouseExited methodSet background of JPanel110OutlineMouseTrackerFrame.java(4 of 4)Declare mouseDragged methodDeclare mouseMoved method111OutlineMouseTrackerFrame.java(1 of 2)112OutlineMouseTrackerFrame.java(2 of 2)11311.14 Adapter ClassesAdapter classImplements event listener interfaceProvides default implementation for all event-handling methods114Software Engineering Observation 11.7 When a class implements an interface, the class has an “is a” relationship with that interface. All direct and indirect subclasses of that class inherit this interface. Thus, an object of a class that extends an event-adapter class is an object of the corresponding event-listener type (e.g., an object of a subclass of MouseAdapter is a MouseListener). 115Extending MouseAdapterMouseAdapterAdapter class for MouseListener and MouseMotionListener interfacesExtending class allows you to override only the methods you wish to use116Common Programming Error 11.4 If you extend an adapter class and misspell the name of the method you are overriding, your method simply becomes another method in the class. This is a logic error that is difficult to detect, since the program will call the empty version of the method inherited from the adapter class. 117Fig. 11.30 | Event-adapter classes and the interfaces they implement in package java.awt.event. 118OutlineMouseDetailsFrame.java(1 of 2)Register event handler119OutlineMouseDetailsFrame.java(2 of 2)Get number of times mouse button was clickedTest for right mouse buttonTest for middle mouse button120OutlineMouseDetails.java(1 of 2)121OutlineMouseDetails.java(2 of 2)12211.15 JPanel Subclass for Drawing with the MouseOverriding class JPanelProvides a dedicated drawing area123Fig. 11.33 | InputEvent methods that help distinguish among left-, center- and right-mouse-button clicks. 124Method paintComponentMethod paintComponentDraws on a Swing componentOverriding method allows you to create custom drawingsMust call superclass method first when overridden125Look-and-Feel Observation 11.13 Most Swing GUI components can be transparent or opaque. If a Swing GUI component is opaque, its background will be cleared when its paintComponent method is called. Only opaque components can display a customized background color. JPanel objects are opaque by default. 126Error-Prevention Tip 11.1 In a JComponent subclass’s paintComponent method, the first statement should always be a call to the superclass’s paintComponent method to ensure that an object of the subclass displays correctly. 127Common Programming Error 11.5 If an overridden paintComponent method does not call the superclass’s version, the subclass component may not display properly. If an overridden paintComponent method calls the superclass’s version after other drawing is performed, the drawing will be erased. 128Defining the Custom Drawing AreaCustomized subclass of JPanelProvides custom drawing areaClass Graphics is used to draw on Swing componentsClass Point represents an x-y coordinate129OutlinePaintPanel.java(1 of 2)Create array of Points130OutlinePaintPanel.java(2 of 2)Anonymous inner class for event handlingOverride mouseDragged methodGet location of mouse cursorRepaint the JFrameGet the x and y-coordinates of the Point131Look-and-Feel Observation 11.14 Calling repaint for a Swing GUI component indicates that the component should be refreshed on the screen as soon as possible. The background of the GUI component is cleared only if the component is opaque. JComponent method setOpaque can be passed a boolean argument indicating whether the component is opaque (true) or transparent (false). 132Look-and-Feel Observation 11.15 Drawing on any GUI component is performed with coordinates that are measured from the upper-left corner (0, 0) of that GUI component, not the upper-left corner of the screen. 133OutlinePainter.java(1 of 2)Create instance of custom drawing panel134OutlinePainter.java(2 of 2)13511.16 Key-Event HandlingKeyListener interfaceFor handling KeyEventsDeclares methods keyPressed, keyReleased and keyTyped136OutlineKeyDemoFrame.java(1 of 3)Implement KeyListener interfaceSet background colorRegister application as event handler for itself137OutlineKeyDemoFrame.java(2 of 3)Declare keyPressed methodGet code of pressed keyDeclare keyReleased methodGet code of released keyDeclare keyTyped methodGet character typed138OutlineKeyDemoFrame.java(3 of 3)Test if it was an action keyDetermine any modifiers pressed139OutlineKeyDemo.java(1 of 2)140OutlineKeyDemo.java(1 of 2)14111.17 Layout ManagersLayout managersProvided to arrange GUI components in a containerProvide basic layout capabilitiesImplement the interface LayoutManager142Look-and-Feel Observation 11.16 Most Java programming environments provide GUI design tools that help a programmer graphically design a GUI; the design tools then write the Java code to create the GUI. Such tools often provide greater control over the size, position and alignment of GUI components than do the built-in layout managers. 143Look-and-Feel Observation 11.17 It is possible to set a Container’s layout to null, which indicates that no layout manager should be used. In a Container without a layout manager, the programmer must position and size the components in the given container and take care that, on resize events, all components are repositioned as necessary. A component’s resize events can be processed by a ComponentListener. 14411.17.1 FlowLayoutFlowLayoutSimplest layout managerComponents are placed left to right in the order they are addedComponents can be left aligned, centered or right aligned145Fig. 11.38 | Layout managers. 146OutlineFlowLayoutFrame.java(1 of 3)Create FlowLayoutSet layout of application147OutlineFlowLayoutFrame.java(2 of 3)Add JButton; FlowLayout will handle placementSet alignment to leftAdjust layoutAdd JButton; FlowLayout will handle placementSet alignment to center148OutlineFlowLayoutFrame.java(3 of 3)Adjust layoutAdd JButton; FlowLayout will handle placementSet alignment to rightAdjust layout149OutlineFlowLayoutDemo.java(1 of 2)150OutlineFlowLayoutDemo.java(2 of 2)15111.17.2 BorderLayoutBorderLayoutArranges components into five regions – north, south, east, west and centerImplements interface LayoutManager2Provides horizontal gap spacing and vertical gap spacing152Look-and-Feel Observation 11.18 Each container can have only one layout manager. Separate containers in the same application can use different layout managers. 153Look-and-Feel Observation 11.19 If no region is specified when adding a Component to a BorderLayout, the layout manager assumes that the Component should be added to region BorderLayout.CENTER. 154Common Programming Error 11.6 When more than one component is added to a region in a BorderLayout, only the last component added to that region will be displayed. There is no error that indicates this problem. 155OutlineBorderLayoutFrame.java(1 of 2)Declare BorderLayout instance variableCreate BorderLayoutSet layoutRegister event handler156OutlineBorderLayoutFrame.java(2 of 2)Add buttons to application using layout manager constantsMake button invisibleMake button visibleUpdate layout157OutlineBorderLayoutDemo.java(1 of 2)horizontal gapvertical gap158OutlineBorderLayoutDemo.java(2 of 2)15911.17.3 GridLayoutGridLayoutDivides container into a gridEvery component has the same width and height160OutlineGridLayoutFrame.java(1 of 2)Declare two GridLayout instance variablesCreate GridLayoutSet layout161OutlineGridLayoutFrame.java(2 of 2)Add button to JFrameUse second layoutUse first layoutUpdate layout162OutlineGridLayoutDemo.java16311.18 Using Panels to Manage More Complex LayoutsComplex GUIs often require multiple panels to arrange their components properly164OutlinePanelFrame.java(1 of 2)Declare a JPanel to hold buttonsCreate JPanelSet layout165OutlinePanelFrame.java(2 of 2)Add button to panelAdd panel to application166OutlinePanelDemo.java16711.19 JTextAreaJTextAreaProvides an area for manipulating multiple lines of textBox containerSubclass of ContainerUses a BoxLayout layout manager168Look-and-Feel Observation 11.20 To provide line-wrapping functionality for a JTextArea, invoke JTextArea method setLine-Wrap with a true argument. 169OutlineTextAreaFrame.java(1 of 2)Declare JTextArea instance variablesCreate a Box containerCreate text area and add to box170OutlineTextAreaFrame.java(2 of 2)Add button to boxCopy selected text from one text area to the otherCreate second text area and add it to box171OutlineTextAreaDemo.java(1 of 2)172OutlineTextAreaDemo.java(2 of 2)173JScrollPane Scrollbar PoliciesJScrollPane has scrollbar policiesHorizontal policiesAlways (HORIZONTAL_SCROLLBAR_ALWAYS)As needed (HORIZONTAL_SCROLLBAR_AS_NEEDED)Never (HORIZONTAL_SCROLLBAR_NEVER)Vertical policiesAlways (VERTICAL_SCROLLBAR_ALWAYS)As needed (VERTICAL_SCROLLBAR_AS_NEEDED)Never (VERTICAL_SCROLLBAR_NEVER)174