OBJECT ORIENTED PROGRAMMING. Java GUI part 1 Loredana STANCIU Room B616

Transcription

1 OBJECT ORIENTED PROGRAMMING Java GUI part 1 Loredana STANCIU loredana.stanciu@upt.ro Room B616

2 What is a user interface That part of a program that interacts with the user of the program: simple command-line interfaces point-and-click graphical user interfaces A common set of tools for graphical user interface design that work on a variety of platforms A user interface toolkit called the Abstract Windowing Toolkit, or the AWT

3 Components and containers A graphical user interface is built of graphical elements called components: buttons, scrollbars, and text fields Components do not stand alone, but rather are found within containers. Contain and control the layout of components

4 Components and containers Components must fit completely within the container Creates a tree of elements, starting with the container at the root of the tree and expanding out to the leaves

5 GUI Graphical User interface

6 Types of components

7 Types of components

8 Button Button() Creates a button Button(String label) Creates a labeled button void addactionlistener(actionlistener l) Adds the specified action listener to receive action events from this button.

9 Button String getlabel() Gets the label of the current button. void setlabel(string label) Sets the button's label to be the specified string.

10 Button example You can create a button by creating an instance of the Button class: Button buttonone = new Button(); Button buttonone = new Button("This is a button"); You can add a button to a frame by using the add() method: aframe.add(buttonone);

11 CheckBox A graphical component that can be in either an "on" (true) or "off" (false) state. setlayout(new GridLayout(3, 1)); add(new Checkbox("one", null, true)); add(new Checkbox("two")); add(new Checkbox("three"));

12 CheckBox Checkbox() Creates a check box with no label Checkbox(String label) Creates a check box with the specified label Checkbox(String label, boolean state) Creates a check box with the specified label and sets the specified state Checkbox(String label, CheckboxGroup group, boolean state,) Creates a check box with the label, set to the state, and in the check box group

13 CheckBox void additemlistener (ItemListener l) Adds the specified item listener to receive item events from this check box. String getlabel() Gets the label of this check box. Boolean getstate() Determines whether this check box is in the "on" or "off" state

14 CheckBox void setcheckboxgroup(checkboxgroup g) Sets this check box's group to be the specified check box group. void setlabel(string label) Sets this check box's label to be the string argument. void setstate(boolean state) Sets the state of this check box to the specified state.

15 CheckboxGroup Used to group together a set of Checkbox buttons. Exactly one check box button in a CheckboxGroup can be in the "on" state at any given time Pushing any button sets its state to "on" and forces any other button that is in the "on" state into the "off" state

16 CheckboxGroup Example setlayout(new GridLayout(3, 1)); CheckboxGroup cbg = new CheckboxGroup(); add(new Checkbox("one", cbg, true)); add(new Checkbox("two", cbg, false)); add(new Checkbox("three", cbg, false));

17 Chioce A pop-up menu of choices. The current choice is displayed as the title of the menu. Choice ColorChooser = new Choice(); ColorChooser.add("Green"); ColorChooser.add("Red"); ColorChooser.add("Blue");

18 Chioce Choice() Creates a new choice menu. void add(string item) Adds an item to this Choice menu. void additemlistener(itemlistener l) Adds the specified item listener to receive item events from this Choice menu. String getitem(int Index) Gets the string at the specified index in this Choice menu.

19 Chioce int getitemcount() Returns the number of items in this Choice menu. int getselectedindex() Returns the index of the currently selected item. String getselecteditem() Gets a representation of the current choice as a string.

20 Chioce void insert(string item, int index) Inserts the item into this choice at the specified position. void remove(int position) Removes an item from the choice menu at the specified position. void remove(string item) Removes the first occurrence of item from the Choice menu.

21 Chioce void removeall() Removes all items from the choice menu. void select(int position) Sets the selected item in this Choice menu to be the item at the specified position. void select(string str) Sets the selected item in this Choice menu to be the item whose name is equal to the specified string.

22 Label A component for placing text in a container. Displays a single line of read-only text. setlayout(new FlowLayout(FlowLayout.CENTER, 10, 10)); add(new Label("Hi There!")); add(new Label("Another Label"));

23 Label Label(String text); Creates a new instance of Label String gettext(); Returns a label s text void settext(string text); Sets a label s text to the specified text

24 Scrollbar Provides a convenient means for allowing a user to select from a range of values. redslider=new Scrollbar(Scrollbar.VERTICAL, 0, 1, 0, 255); add(redslider); ranger = new Scrollbar(Scrollbar.HORIZONTAL, 0, 60, 0, 300); add(ranger);

25 Scrollbar Scrollbar() Constructs a new vertical scroll bar. Scrollbar(int orientation) Constructs a new scroll bar with the specified orientation.

26 Scrollbar Scrollbar(int orientation, int value, int visible, int minimum, int maximum) Constructs a new scroll bar with the specified orientation, initial value, visible amount, and minimum and maximum values. void addadjunstmentlistener(adjust mentlistener l) Adds the specified adjustment listener to receive instances of AdjustmentEvent from this scroll bar.

27 TextField A text component that allows for the editing of a single line of text. TextField tf1, tf2, tf3, tf4; tf1 = new TextField(); tf2 = new TextField("", 20); tf3 = new TextField("Hello!"); tf4 = new TextField("Hello", 30);

28 TextField TextField() Creates a new instance of TextField TextField(String text) Creates a new instance of TextField with the specified text void setcolumns(int columns) Sets the number of columns in a textbox void settext(string text) Sets a textfield text to the specified text

29 List A scrolling list of text items. The list can be set up so that the user can choose either one item or multiple items. List lst = new List(4, false); lst.add("mercury"); lst.add("venus"); lst.add("earth"); lst.add("javasoft"); lst.add("mars"); lst.add("jupiter"); lst.add("saturn"); lst.add("uranus"); lst.add("neptune"); lst.add("pluto");

30 List List() Creates a new scrolling list. List(int row) Creates a new scrolling list initialized with the specified number of visible lines. List(int rows, boolean multiplemode) Creates a new scrolling list initialized to display the specified number of rows.

31 List void add(string item) Adds the specified item to the end of scrolling list. void add(string item, int index) Adds the specified item to the the scrolling list at the position indicated by the index. void addactionlistener(actionlistener l) Adds the specified action listener to receive action events from this list.

32 List void remove( int position) Removes the item at the specified position from this scrolling list. void remove( String item) Removes the first occurrence of an item from the list. void removeall() Removes all items from this list.

33 List void replaceitem(string value, int index) Replaces the item at the specified index in the scrolling list with the new string. void select(int index) Selects the item at the specified index in the scrolling list.

34 TextArea A multi-line region that displays text. It can be set to allow editing or to be read-only. new TextArea("Hello", 5, 40);

35 TextArea TextArea(int rows, int columns) Constructs a new text area with the specified number of rows and columns and the empty string as text. TextArea(String text) Constructs a new text area with the specified text. TextArea(String text, int rows, int columns) Constructs a new text area with the specified text, and with the specified number of rows and columns.

36 TextArea TextArea(String text, int rows, int columns, int scrollbars) Constructs a new text area with the specified text, and with the rows, columns, and scroll bar visibility as specified. void append(string str) Appends the given text to the text area's current text. void insert(string str, int position) Inserts the specified text at the specified position in this text area.

37 Types of containers Window A top-level display surface (a window) An instance of the Window class has no border and no title Frame A top-level display surface (a window) with a border and title An instance of the Frame class may have a menu bar

38 Types of containers Dialog A top-level display surface (a window) with a border and title An instance of the Dialog class cannot exist without an associated instance of the Frame class. Panel A generic container for holding components. An instance of the Panel class provides a container to which to add components.

39 FRAMES A top-level window with a title and a border. It has minimize, maximize, and close buttons in its top right corner and can be moved and resized (by default) Frames are created using the Frame class

40 FRAMES Frame() Creates a new instance of Frame that is initially invisible Frame(String title) Creates a new instance of Frame that is initially invisible with the specified title NOTE: Initially, a frame will not be visible. You have to set it to be visible using the setvisible() method

41 FRAMES boolean isresizable() Returns a boolean value indicating whether a frame is resizable or not void setresizable(boolean resizable) Sets whether or not a frame is resizable void isvisible(boolean isvisible) Sets whether or not a frame is visible

42 FRAMES String gettitle() Returns the title of a frame void settitle(string title) Sets the title of a frame void setsize(int width, int height) Sets the size of a frame void setlocation(int xcoord, int ycoord) Sets the location of the window

43 Frames Frames are capable of generating the following types of WindowEvents: WINDOW_OPENED WINDOW_CLOSING WINDOW_CLOSED WINDOW_ICONIFIED WINDOW_DEICONIFIED WINDOW_ACTIVATED WINDOW_DEACTIVATED WINDOW_GAINED_FOCUS WINDOW_LOST_FOCUS WINDOW_STATE_CHANGED

44 Frames Example You can create a frame creating an instance of class Frame: import java.awt.*; class MyFrame { public static void main(){ Frame frame = new Frame("My title"); frame.setsize(200, 200); frame.setvisible(true); }}

45 Dialog A top-level window with a title and a border that is typically used to take some form of input from the user. The size of the dialog includes any area designated for the border. A dialog must have either a frame or another dialog defined as its owner when it's constructed.

46 Dialog Dialog(Dialog owner) Constructs an initially invisible, non-modal Dialog with an empty title and the specified owner dialog. Dialog(Dialog owner, String title) Constructs an initially invisible, non-modal Dialog with the specified owner dialog and title. Dialog(Frame owner) Constructs an initially invisible, non-modal Dialog with an empty title and the specified owner frame.

47 Dialog Dialog(Frame owner, String title) Constructs an initially invisible, non-modal Dialog with the specified owner frame and title. String gettitle() Gets the title of the dialog. void hide() Hides the Dialog and then causes show() to return if it is currently blocked.

48 Dialog void show() Makes the Dialog visible. void setresizable(boolean resizable) Sets whether this dialog is resizable by the user. void settitle(string title) Sets the title of the Dialog.

49 Panel The simplest container class Provides space in which an application can attach any other component, including other panels. The default layout manager for a panel is the FlowLayout layout manager.

50 Panel Panel() Creates a new panel using the default layout manager. Panel(LayoutManager layout) Creates a new panel with the specified layout manager. void add( ) Add a component to the panel void remove( ) Remove a component from the panel

51 Creating a container When building an application, the programmer must first create an instance of class Window or class Frame import java.awt.*; public class Example1 { public static void main(string [] args) { } } Frame f = new Frame("Example 1"); f.show();

52 Java GUI Layout Creating a graphical user interface and elements for it alone is not enough, you have to know where and how to place these graphical elements There are classes called layout managers, which decide where and how components will be placed Layout manager classes are located in the java.awt package

53 Flowlayout Arranges components in a left-to-right flow, much like lines of text in a paragraph. Flow layouts are typically used to arrange buttons in a panel. It will arrange buttons left to right until no more buttons fit on the same line. Each line is centered.

54 Flowlayout FlowLayout() Creates a new instance of FlowLayout FlowLayout(int align) Creates a new instance of FlowLayout with the specified alignment. Possible values: CENTER LEADING LEFT WRITE

55 Flowlayout FlowLayout(int align, int hgap, int vgap) Creates a new flow layout manager with the indicated alignment and the indicated horizontal and vertical gaps. You can set a frame to use FlowLayout by using the setlayout() method: frame.setlayout(new FlowLayout());

56 Flowlayout Example

57 GridLayout Is used to arrange components in a grid of equally sized rectangular cells GridLayout() Creates a new GridLayout which has one row by default GridLayout(int rows, int columns) Creates a new GridLayout with the specified number of rows and columns

58 GridLayout You can set a frame to use GridLayout by using the setlayout() method: frame.setlayout(new GridLayout(2,2);

59 Borderlayout Lays out a container, arranging and resizing its components to fit in five regions: north, south, east, west, and center. Each region may contain no more than one component, and is identified by a corresponding constant: NORTH, SOUTH, EAST, WEST, and CENTER Components start at their preferred size, but are expanded as needed to fill the region they are in

60 Borderlayout BorderLayout() The default constructor (no space between regions) BorderLayout(int hnp, int vnp) A constructor which specifies the number of pixels between regions You can set a frame to use BorderLayout by using the setlayout() method: frame.setlayout(new BorderLayout(5,5);

61 Borderlayout When an element is added, the location of that element must be specified: frame.add( North,buttonOne);

62 Java event handling Event handling in Java refers to executing some code when specific actions occur such as a window being minimized or a button being clicked There are special interfaces for this purpose and they are located in the java.awt.event package

63 Handling window events To handle window events, the WindowListener interface is used The class that handle window events must implement this interface The WindowListener interface has various methods to handle window events These methods are presented on the following slides

64 Methods of the WindowListener interface windowopened(windowevent e) Called when a window first becomes visible windowactivated(windowevent e) Called when a window has become active (meaning it is able to accept input events) windowdeactivated(windowevent e) Called when a window is deactivated (meaning it has lost input focus)

65 Methods of the WindowListener interface windowiconified(windowevent e) Called when a window is iconified (minimized) windowdeiconified(windowevent e) Called when a window has been restored from a minimized state windowclosing(windowevent e) Called when a user attempts to close a frame windowclosed(windowevent e) Called when a window is closed

66 Handling action events To handle action events (such as the clicking of a button), the ActionListener interface is used Method of the ActionListener interface: actionperformed(actionevent e) Called when an action has occurred

67 Handling focus events To handle focus events (such as when an object such as a textbox is awaiting user input), the FocusListener interface is used Methods of the FocusListener interface: focusgained(focusevent e) Called when an object gains focus focuslost(focusevent e) Called when an object loses focus

68 Handling item events Item events are triggered by components that allow for a selection of items such as Checkboxes To handle item events, the ItemListener interface is used Method of the ItemListener interface: itemstatechanged(itemevent e) Called when the state of an item has changed

69 Handling text events Text events are triggered by components whose fields are editable such as textboxes To handle text events, the TextListener interface is used Method of the TextListener interface: textvaluechanged(textevent e) Called when the data in a field of a component has changed

70 Handling mouse events Mouse events are triggered by the computers mouse Mouse events are actually handled by two interfaces: MouseListener: used to detect the clicking of mouse buttons or the moving of a mouse into or out of a listener's area MouseMotionListener: used to detect the movement of the mouse

71 Methods of the MouseListener interface mouseclicked(mouseevent e) Called when a mouse button is clicked mouseentered(mouseevent e) Called when the mouse enters a source components area

72 Methods of the MouseMotionListener interface mousemoved(mouseevent e) Called when the mouse is moved while in a components area mousedragged(mouseevent e) Called when the mouse moves while a mouse button is down while within a components area

73 Handling key events Key events are triggered by keyboard actions Key events are handled by the KeyListener interface Methods of the KeyListener interface: keypressed(keyevent e) Called when a key is pressed down keyreleased(keyevent e) Called when a key is released keytyped(keyevent e) Called when a key is typed

74 Making objects listen for events Once you implement the necessary interfaces, and define the implementation of their methods, you need to make objects listen for events Example: if you implement the ActionListener interface, and you define what its actionperformed() method does, and you want the method to be called every time a certain button is clicked, you need to make that button listen for the event

75 Listen for action events For action events use the addactionlistener() method Example: //create a button Button abutton = new Button("This is a button"); //specify that this button listens for action events abutton.addactionlistener(this);

76 Listen for action events The class that contains the previous button must implement the interface ActionListener, so it will have a function actionperformed(actionevent e) You can find the source of this event calling the function e.getsource() This function will return an element of type Object

77 Listen for focus events For focus events use the addfocuslistener() method Example: //create a textbox TextField atextfield = new TextField("This is a textbox"); /*specify that this textbox listens for focus events*/ atextfield.addfocuslistener(this);

78 Listen for item events For item events use the additemlistener() method Example: //create a checkbox CheckBox chkbox1 = new CheckBox("This is a checkbox", false); /*specify that this checkbox listens for item events*/ chkbox1.additemlistener(this);

79 Listen for text events For text events use the addtextlistener() method Example: //create a textbox TextField atextfield = new TextField("This is a textbox"); /*specify that this textbox listens for text events*/ atextfield.addtextlistener(this);

80 Listen for mouse events For mouse events use the addmouselistener() method Example: //create a frame Frame aframe = new Frame(); /*specify that this frame listens for mouse events*/ aframe.addmouselistener(this);

81 Listen for mouse motion events For mouse motion events use the addmousemotionlistener() method Example: //create a frame Frame aframe = new Frame(); /*specify that this frame listens for mouse motion events*/ aframe.addmousemotionlistener(this);

82 Listen for key events For key events use the addkeylistener() method Example: //create a textbox TextField atextfield = new TextField("This is a textbox"); /*specify that this textbox listens for key events*/ atextfield.addkeylistener(this);

83 Problem Create a GUI in Java containing a TextField, a TextArea and a Choice. Clicking the button Save from text field, save the content of the TextField into the TextArea and clear the TextField. This operation can be done only if the button is enabled using a Checkbox. Clicking the button Save from choice save the current selection into the TextArea. If the content of the TextField is e stop the application.

84 Solution

85 Solution import java.awt.*; import java.awt.event.*; class MyFrame extends WindowAdapter implements KeyListener, ActionListener, ItemListener{ Frame frame; TextField atextfield; TextArea atextarea; Checkbox be; Button b1,b2; Choice c1;

86 Solution public static void main(string []args){ MyFrame f = new MyFrame(); f.init(); } public void init(){ frame = new Frame( Problem C8"); frame.setsize(500, 350); frame.setvisible(true); frame.addwindowlistener(this); frame.setlayout(new BorderLayout(5,5));...

87 Solution... Panel p1 = new Panel(); p1.setlayout(new GridLayout(2,2,10,10)); Panel p2 = new Panel(); p2.setlayout(new FlowLayout()); b1 = new Button("Save from text field"); b1.setenabled(false); p1.add(b1); b1.addactionlistener(this); p1.add(be = new Checkbox("Button enable", null, false)); be.additemlistener(this);...

88 Solution... b2 = new Button("Save from choice"); b2.addactionlistener(this); p1.add(b2); Label l = new Label("Enter text"); p2.add(l); atextfield = new TextField("",20); p2.add(atextfield); Label l2 = new Label("Select"); p2.add(l2);...

89 Solution... c1 = new Choice(); c1.add("object"); c1.add("oriented"); c1.add("programming"); p2.add(c1); frame.add("north",p2); Label l3 = new Label("Save resuls here"); frame.add("west",l3); frame.add("east",new Label(" ")); atextarea = new TextArea("",10,20); frame.add("center",atextarea); atextfield.addkeylistener(this); frame.add("south",p1);}...

90 Solution... public void actionperformed(actionevent e){ if(e.getsource()==b1) { else atextarea.append(string.format("%s\n", atextfield.gettext())); atextfield.settext("");} TextArea.append(String.format("%s\n",c1. getselecteditem()))}...

91 Solution... public void itemstatechanged(itemevent e){ if(e.getstatechange()==1) b1.setenabled(true); else b1.setenabled(false);} public void keytyped(keyevent e){ if(e.getkeychar()=='e'&& b1.isenabled()) System.exit(0);} public void keyreleased(keyevent e){} public void keypressed(keyevent e){} public void windowclosing(windowevent e) { System.exit(0); }}

92 References Todd Sundsted, Introduction to the AWT. A description of Java s user interface toolkit,