Cutting edge Programming/Practicum15-200

IntroductionIn this lecture we will start experimenting the View part of the Model-View-Controller (MVC) pattern for writing GUI applications.We will mostly discuss the JFrame and also JPanel classes: 2 instrumental classes (characterized in the javax.swing package) that programmers extfinish as soon as composing GUIs.We will compose these classes independently here, yet periodically utilizing inner classes simplifies their code.Basically, a JFrame represents a framed home window and a JPanel represents some area in which controls (e.g., buttons, checkboxes, and textfields) and also visuals (e.g., numbers, photos, and also text) can show up.Windows have the right to contain/display multiple panels, although in the most basic GUIs, we will associate just one panel through a home window.When we comment on JFrames and also JPanels, we will comment on just an extremely few of their many kind of methods: they are extremely subclassed (in a deep hierarchy) and also therefore inherit many kind of (many) exciting approaches.We will certainly talk about just the the majority of advantageous and also vital of these methods: the ones provided in the majority of GUI applications.When analysis this lecture (and programming using these classes) you have to always have a Javadoc web browser open, and also not be afraid to search it for some beneficial method.In the procedure of pointing out JFrame and also JPanels,, we will additionally talk about a organize of other helpful (and also simpler) classes: Toolkit, Image, Dimension, Point, Color, Font,, and classes are imported and also then supplied in many GUI applications.We use the last,, to render visuals (e.g., numbers, pictures, and also also text) in a JPanel that includes the component of a JFrame.Students at this suggest in the course are meant to have the ability to review the Javadoc of these classes (in Sun"s API) to learn about their framework and also usage and also to explore assorted techniques (whose names suggest they could be useful).Note that some of these classes declare static approaches and also fields (largely constants), which are quickly spotted bereason their offers in our programs are prechallenged by the name of the class (whose initially letter is capitalized).We will additionally start to comment on the idea of listeners and adapters, which we will certainly use a lot even more broadly when we talk about the Controller part of the MVC pattern.Finally, we will certainly research a little of manage flow in GUIs: exactly how techniques are called: in Java they can be dubbed explicitly as well as implicitly.Tright here is a folder that contains miscellaneous jobs linked with this lecture. Please downpack View Demonstrations and also unzip this folder and also examine its contents briefly now (we will refer to details later).

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The JFrame ClassFor many GUIs enforced via the MVC pattern, we create their View course by subclassing the JFrame class (which is characterized in the javax.swing package).Swing is a collection of associated classes for writing stand-alone Java applications: applets are written using various other Java packages.Tbelow are whole books composed on just how to usage Swing.By extfinishing JFrame, the View subclass inherits thousands of techniques from not only JFrame, yet its superclasses: the JFrame course is in a pecking order whose superclasses encompass (going upward) Frame, Window, Container, Component, and also finally Object).At the top of this heirarchy is the Component class, which is abstract; objects from its concrete subclasses are displayable on the screen, and also have the adhering to vital techniques (together with many type of many more): isVisible/setVisible (with a boolean parameter), getSize/setSize (through either a Dimension or two int parameters), getLocation/setLocation (with either a Point or 2 int parameters), and repaint (parameterless).The Container class is itself taken into consideration a Component, however one that in enhancement collects together other Components, making use of a LayoutManager (debated in the next lecture) to organize them visually; it takes the function of a compowebsite pattern: once we percreate an procedure on a Container, it performs that operation on all its Components.The Window class represents a raw home window (e.g., no border) via its own internal coordinate system: (0,0) is the home windows upper-left hand corner.The Frame course represents a home window with Border and title location (we deserve to specify various kinds of borders and also set its associated icon/title).Finally, the JFrame course represents a Java compatible window: it has an associated content pane, which shows its visual contents.Generally we specify a parameterless constructor and one brand-new strategy named build, which calls many type of of these inherited techniques to initialize the JFrame"s window; this technique is referred to as in the main strategy in Application (after building the model, check out, and controller).For the most basic GUIs, this is not strictly necessary: we can put all this code in the constructor for the class itself; however for even more facility GUIs, separating construction from structure is much better.A JFrame appears as a traditional window; the one we will use in the earlist component of this lecture displays as complies with.
Eextremely pixel (picture element) on a computer display is represented by a shade, which is a mix of exactly how a lot red, green, and blue show up tbelow.The upper-left hand also edge of the screen has actually an x coordinate of 0 and also a y coordinate 0; hence x works with increase from left to best, and y works with rise from optimal to bottom (unlike our conventional coordinate system).The bottom-ideal hand also corner has actually the largest x and y collaborates (this number varies, depending on the size of the screen): a representative high-resolution worth is 1280 horizontal by 1024 vertical pixels (for a full of 1,310,720 pixels).Each JFrame (because it is a subclass of Component) has a place on the screen (for its upper-left hand corner) and dimension.Two simple JFrame approaches (inherited from Component) are getLocation which retransforms a Point object (which has actually public circumstances variables x and y) and getSize which retransforms a Dimension object (which has actually public circumstances variables height and also width).Likewise, it has setLocation and setSize approaches, which usage objects from these classes as parameters, or just 2 int parameters.Each JFrame (because it is a subcourse of Frame), has actually a header that has (going left to right) an symbol (little picture; it is optional), a title (text), and means to the appropriate three home window manage buttons(minimize, midimize/maximize, and also terminate).We deserve to adjust the appearance of the icon by utilizing the technique setIconImage; we have the right to change the title making use of the strategy setTitle.Likewise there are getIconImage and also getTitle techniques.To check out an symbol from a record and put it right into the header first requires calling the getImage method in the Toolkit course, passing its result to the setIconImage approach.The getImage method deserve to be referred to as through a String parameter that names the file that stores the icon (in .gif, .jpeg, .png format).It retransforms a recommendation to an Image of that icon (or null if the file cannot be found, or it does not save information of the compelled type).Here is the standard code to percreate all these operations; the techniques are referred to as inside the View class: Toolkit tk = Toolkit.getDefaultToolkit(); Image titleIcon = tk.getImage(gifFileName); setIconImage(titleIcon);Notice how a Toolkit object is gotten: through the static getDefaultToolkit technique from the Toolkit class, not by building.Technically, even this short code deserve to be streamlined to Toolkit tk = Toolkit.getDefaultToolkit(); setIconImage(tk.getImage(gifFileName));We cannot change the appearance of the window manage butlots, yet we have the right to readjust the habits of each (using the technique addWindowListener, which we talk about below).This method is inherited from the Window superclass.The JFrame stores a referral to its content pane.The JFrame course itself defines getContentPane and also setContentPane methods; the content pane itself is a Container.When we learn about the JPanel class we will certainly discover this connection better.In the most basic the content pane is simply one panel; but, we can use the add strategy (inherited in Container) to add many Components into the content pane of a JFrame; Java uses a layout manager (it is told which one to use using setLayoutManager) to determine the just how these components are arrangedLayout managers are the topic of the next lecture.We will certainly additionally check out that eexceptionally JPanel has actually its own coordinate device, via (0,0) as the upper-left hand also corner, which significantly simplifies programming it.Finally, the strategy setVisible (via a boolean parameter) determines whether a JFrame shows up on (or disappears from) the screen.
AdaptersAn adapter is a type of pattern.Typically, it is a concrete course through a selection of stub methods (generally void techniques that instantly return) that deserve to be overriden.For instance, the WindowAdapter course contains the complying with methods (view Javadoc for even more details), which are dubbed as soon as the user clicks a window control button: WindowActivated, WindowClosed, WindowDeactivated, WindowClosing, WindowIconified, WindowDeiconified, and also WindowOpened.In the WindowAdapter course, these approaches just return instantly, without doing anything (yet these approaches exist, and are referred to as once the user clicks a home window control button).The JFrame course inherits (from the Window class) the addWindowListener method from the Window superclass.It "listens" for certain components being clicked and also speak to the correct strategy for each component.Its parameter have to be a referral to a things constructed from a class that implements an interchallenge called WindowListener.In fact, the WindowAdapter class implements this interconfront by defining each of its methods, as a stubs.Thus we have the right to compose in a JFrame method addWindowListener(new WindowAdapter());Of course, bereason eextremely strategy in this class does nopoint, we have actually included no brand-new exciting habits to the JFrame with this method call.But now, let"s specify some amazing behavior as soon as the window is closed.We can define the following course. public class Terminator exoften tends WindowAdapter public void windowClosing(WindowEvent e) System.out.println("Window closing selected: terminating program"); System.exit(0); Java gives a default constructor for the Terminator class.This class inherits all the stub methods from the WindowAdapter supercourse, however it overrides the windowClosing strategy (the code inside says that as soon as the user clicks the terminate switch on this window, print a message, and the entire regimen itself that produced the window should terminate).Note that this course implements the WindowListener interface: we can specifically say it does, or as illlustrated over, not say it: Java knows that any kind of subcourse (of a course that implements an interface) also implements that interchallenge, because at worst it simply inherits all of the needed methods.Given this course, we have the right to write addWindowListener(new Terminator()); to provide the JFrame the new actions that we desire.Notice that we are specifying this subclass just to construct one circumstances of it, to pass to the addWindowListener approach.This is precisely what anonymous classes are beneficial for: to supply a more compact (yet complex) syntaxation for building one object from a course that is never required again.Recall that it requires building an object from an anonymous (nameless) course.The syntaxation in this situation is addWindowListener(brand-new WindowAdapter() public void windowClosing(WindowEvent e) System.out.println("Window nlinux.orghedding selected: terminating program"); System.exit(0); ); Here we say brand-new WindowAdapter() yet automatically follow it by a block that overrides only the windowClosing strategy from that class (we can override any variety of these methods).It says to Java, construct an item from an anonymous subcourse whose supercourse is WindowAdapter; the anonymous subclass exhas a tendency WindowAdapter, inheriting all its techniques and overriding just the windowClosing technique.Note that we have discussed 2 different concepts right here.The principle of an adapter course (which implements an interchallenge with stub methods). We can usage such classes straight or even more most likely construct subclasses of them (and also then use objects constructed from these subclasses instead). The essential to an adapter course is that it already implements an interconfront, with default strategy meanings; we have the right to quickly create a subcourse from it, overriding an approach or two, to specify different habits for some action(s). The idea of an anonymous course (based on an adapter class). When we need to construct just one object from a subcourse, we don"t really also have to name the subcourse. Instead, we deserve to usage special Java syntax to construct a things from a subclass of a called superclass by specifying the superclass name and the overridden methods.We will view adapter classes offered generally for other kinds of listeners (butlots, mouse, keyboard) once we study the Controller component of the MVC pattern.It is a general technique that we have the right to use in other areas in Java programs too.
Sample JFrame ProgramsExamine the folder named standard jframe in the View Demonstrations downfill.It mirrors a brief program (little View class and tiny Application class) that illustrates just how to usage javax.swing.JFrame.The console controls this home window appearing and disshowing up.The JFrame"s dimension is always at 1/2 the width/height of the display.Its header consists of an symbol and also title (which alters slightly, through a counter/place, each time the window shows up.The window"s location transforms each time it disshows up. When the home window is closed, the entire regimen terminates (consisting of the loop in main).You can experiment through the techniques dubbed to attempt to gain other creates of interesting habits, including distinct actions for other techniques mentioned by the WindowAdapter.
The JPanel ClassOnce we write a JFrame for our GUI, we often add one or more objects to it, each from a subcourse extfinishing JPanel.Normally, each sublcass will specify some instance variables and a constructor (to initialize them), and also overrides the inherited paintComponent approach with one that is special to the subcourse.The paintComponent approach determines what numbers, imeras, and/or text (controls prefer buttons and also textfields are painted automatically) appear on the component of the screen that is owned by the JPanel.To override the inherited paintComponent strategy, we need to compose a void strategy through one parameter: a referral to a things of type (referred to as the context: watch the following area for a short discussion of this class), which consists of all the methods for illustration numbers, imperiods, and also message (see its Javadoc for details).The Java runtime system automatically calls this paintComponent approach whenever the size of its JFrame is readjusted, whenever before other windows are moved to uncover component of the JFrame, and also whenever before the JFrame is deiconified after being iconified (subclasses of the WindowAdapter have the right to add unique behavior for such events as well).In all cases, the paintComponent method is dubbed to rescreen the contents of the JPanel, now that the amount of it that is visible has been "changed".The Java runtime instantly gives the paintComponent strategy via the right conmessage (we never before need to concern about that).If we desire to explicitly speak to the paintComponent method, say contact it repeatedly to pressure Java to animate some actions in a JPanel, we cannot call it directly, because we cannot accessibility its context.Instead, we must speak to the void, parametermuch less approach repaint (either on a particular JPanel or on its JFrame, which immediately calls it on each JPanel in its content pane).The biggest conceptual trouble that students have actually around GUIs is that they THINK the screen stores all the indevelopment created to it.When a JPanel paints itself, all the numbers, imeras, and also text are written into the screen: some are visible, some are not (because they go past the window"s boundary, or is extended by one more window).The concealed indevelopment is GONE.If the JPanel demands to redisplay any kind of part of itself, it have the right to carry out so only by calling paintComponent aacquire (which typically displays it all).For sophisticated applications, overloaded versions of the paintComponent approach could have the ability to determine what component of its photo to repaint, yet in simple applications, it simply repaints whatever.So, if we should display screen a bunch of objects in a JPanel, we must keep indevelopment around each of these objects (say in a repertoire class), and then the paintComponent approach must iteprice through this repertoire, displaying each object in the JPanel
JPanel, paintComponent, and the ContextWhenever before the paintComponent technique of a JPanel is referred to as (whether by the Java system or the program itself), it is offered through a reference to a things from the course (dubbed its context).The context stores state, including wright here on the display the upper-left hand also edge of the JPanel is, what is the existing color for drawing/message, etc.It does not save anything drawn in the JPanel.The paintComponent strategy general supplies approaches from the class to draw lines, rectangles, ovals, imperiods, and also text.In the process, it have the right to readjust some of these states.In the following few sections, we will certainly explain exactly how to screen numbers, images, message, and butloads in such a panel.Keep in mind that eincredibly JPanel objects inherits from Component the getBackground and setBackground techniques, which has actually a Color as rerevolve value/parameter respectively.Finally, we must constantly call super.paintComponent() prior to doing anything graphical in the paintComponent approach.
Drawing FiguresIn this area we will certainly study some easy techniques for illustration numbers in a conmessage.First of all, whenever we specify works with, the conmessage will certainly analyze them so that (0,0) is the upper-left hand also edge of the JPanel.Parts of illustrations might go beyond the screen.This is not an error: such components simply will not be watched.Whenever before we specify the x and also y collaborates of a figure, they refer to the upper-left hand also of the number (NOT ITS CENTER).Here are prototypes for the simplest drawing techniques in the course. void drawArc(int x, int y, int width, int elevation, int startAngle, int arcAngle) void drawLine(int x1, int y1, int x2, int y2) void drawOval(int x, int y, int width, int height) void drawPolygon(int<> xPoints, int<> yPoints, int nPoints) void drawPolygon(Polygon p) void drawPolyline(int<> xPoints, int<> yPoints, int nPoints) void drawRect(int x, int y, int width, int height) void drawRoundRect(int x, int y, int width, int elevation, int arcWidth, int arcHeight)Line are straight lines;ovals are drawn via the stated significant and minor axes (circles have actually these axes the same);a polygon is mentioned either by either 2 parallel arrays of equivalent x and y collaborates, or a Polygon object (view Javadoc) which stores such arrays internally (and also deserve to identify whether a suggest is in a polygon);a polyline is favor a polygon, however its last allude is not associated to its first;rectangles come in two flavors: square corners and rounded corners (squares simply have their width and also height the very same.Likewise, tbelow are simlar techniques that attract filled-in forms. void fillArc(int x, int y, int width, int height, int startAngle, int arcAngle) void fillOval(int x, int y, int width, int height) void fillPolygon(int<> xPoints, int<> yPoints, int nPoints) void fillPolygon(Polygon p) void fillRect(int x, int y, int width, int height) void fillRoundRect(int x, int y, int width, int elevation, int arcWidth, int arcHeight)A huge selection of numbers can be drawn through combinations of these approaches.Note that we deserve to contact the getBackground strategy of a Component; by drawing somepoint in this color (utilizing the setColor method), Java will certainly seem to erase what it underneath it.Examine the folder named numbers jpanel in the View Demonstrations download.It mirrors a short routine (little DrawPanel course, tiny View and Application class) that illustrates how to usage javax.swing.JPanel for illustration numbers in a JFrame.
Drawing ImagesIn this area we will study two basic techniques for drawing images in a conmessage.We have currently seen just how to check out images stored in files with a Toolkit.We will certainly currently check out just how to render such imperiods directly and exactly how to render them after scaling them.Here are protokinds for the easiest photo approaches in the class. boolean drawImage(Image img, int x, int y, ImageObserver observer) boolean drawImage(Image img, int x, int y, int width, int elevation, ImageObserver observer)The x and also y values specify the upper-left hand of the picture.The initially technique provides the image in it actual size; the second shrinks or broadens it to the dimensions width and also height.For currently, we will specify null for the ImageObserverExamine the folder called images jpanel in the View Demonstrations download.It reflects a brief routine (little DrawPanel class, tiny View and also Application class) that illustrates exactly how to usage javax.swing.JPanel for drawing images.It draws a bunch of warm dogs, and also moves them a little bit each time enter is pressed in the console home window.
Drawing TextIn this section we will certainly research some easy methods for illustration message in a conmessage.The procedure is straightforward, however it have the right to involve two various other exciting classes, Font and in the Font course are created, specified by a font name (e.g., SanSerif), style (e.g., plain, bold, italic), and size (e.g., 12 point: stated in points, which is 1/72 of an inch).Objects in the class explain a font, via several interesting information: the height and also width of personalities in the font, ascent and also descent, and so on.Here are protokinds for the easiest message approaches in the class. void drawString(String str, int x, int y) Font getFont() f) void setFont(Font font)Note: the x and y worths specify the baseline of the the message, not its upper-left hand also (the baseline is the bottom of the character, not including the descender).The initially strategy provides the message (making use of the present font and color) founding at the stated coordinate.Before this statement we might write the adhering to code to specify the font to use and gain its Font f1 = new Font("SansSerif", Font.BOLD, 14); f1m =; g.setFont(f1); g.setColor(;With any object we have the right to call the stringWidth approach with any type of String: it retransforms the width of that String using that FontExamine the folder named message jpanel in the View Demonstrations downfill.It reflects a short routine (little DrawPanel class, tiny View and also Application class) that illustprices just how to use javax.swing.JPanel for drawing message.It additionally illustprices some uses of the Font and classes, which are both identified in the java.awt package.
ButtonsFinally, in this area we will research how to put buttons in JPanels.Here we usage Butloads only for their visual effect; in the lecture on Controllers we will learn how to make pressed buttons call correct techniques in the Model.Standard butloads are built from the JButton class (in the javax.swing package).As with other controls, they inherit thousands of techniques.The typical constructor mentions a String to use as a label for the switch (or we can call setLabel via any type of String later).We can likewise contact inherited methods such as setFont, setBackground, and setForeground, although the majority of typical butloads usage default values for these.We have the right to also contact the setEnabled strategy (via a boolean parameter) to tell Java whether a button is pressable (if not, its label will certainly appear as a faded color).Here is an example of advertising a JButton and percreating many type of of these operations.

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JButton b = new JButton("Cold"); b.setFont(brand-new Font("Monospaced",Font.BOLD,12)); b.setBackground(Color.yellow); b.setForeground(;Finally, we can usage the add strategy to add any kind of Component to a JPanel.In the routine listed below, we initially construct a JPanel and save its value in a neighborhood variable, and also then call add multiple times, once to put each button in the panel.Recontact that a unique layout manager (which we will cover in the following lecture) determines where each switch will go.Examine the folder called button jpanel in the View Demonstrations download.It reflects a brief program (tiny DrawPanel class, tiny View course and also tiny Application class) that illustrates how to use javax.swing.JPanel for illustration butloads.
Problem Set To encertain that you understand all the material in this lecture, please resolve the the announced troubles after you read the lecture. If you get stumped on any type of problem, go back and also check out the relevant part of the lecture. If you still have actually inquiries, please get aid from the Instructor, a CA, or any type of various other student. None yet.