Typically we define a parameterless constructor and one new method named build , which calls many of these inherited methods to initialize the JFrame 's window; this method is called in the main method in Application after constructing the model, view, and controller.
For the simplest GUIs, this is not strictly necessary: we can put all this code in the constructor for the class itself; but for more complicated GUIs, separating construction from building is better.
A JFrame appears as a standard window; the one we will use in the earlist part of this lecture displays as follows. Every pixel picture element on a computer screen is represented by a color, which is a combination of how much red, green, and blue appear there.
The upper-left hand corner of the screen has an x coordinate of 0 and a y coordinate 0 ; thus x coordinates increase from left to right, and y coordinates increase from top to bottom unlike our standard coordinate system. The bottom-right hand corner has the largest x and y coordinates this number varies, depending on the size of the screen : a representative high-resolution value is horizontal by vertical pixels for a total of 1,, pixels.
Each JFrame because it is a subclass of Component has a location on the screen for its upper-left hand corner and size. Two simple JFrame methods inherited from Component are getLocation which returns a Point object which has public instance variables x and y and getSize which returns a Dimension object which has public instance variables height and width. Likewise, it has setLocation and setSize methods, which use objects from these classes as parameters, or just two int parameters.
We can change the appearance of the icon by using the method setIconImage ; we can change the title using the method setTitle. Likewise there are getIconImage and getTitle methods. To read an icon from a file and put it into the header first requires calling the getImage method in the Toolkit class, passing its result to the setIconImage method.
The getImage method can be called with a String parameter that names the file that stores the icon in. It returns a reference to an Image of that icon or null if the file cannot be found, or it does not store information of the required type. This method is inherited from the Window superclass. The JFrame stores a reference to its content pane.
When we learn about the JPanel class we will explore this connection further. In the simplest the content pane is just one panel; but, we can use the add method inherited in Container to add many Component s into the content pane of a JFrame ; Java uses a layout manager it is told which one to use via setLayoutManager to determine the how these components are arranged Layout managers are the topic of the next lecture.
We will also see that every JPanel has its own coordinate system, with 0,0 as the upper-left hand corner, which greatly simplifies programming it. Finally, the method setVisible with a boolean parameter determines whether a JFrame appears on or disappears from the screen. An adapter is a kind of pattern. Typically, it is a concrete class with a variety of stub methods typically void methods that immediately return that can be overriden. In the WindowAdapter class, these methods just return immediately, without doing anything but these methods exist, and are called when the user clicks a window control button.
It "listens" for certain components being clicked and call the appropriate method for each component. Its parameter must be a reference to an object constructed from a class that implements an interface named WindowListener. In fact, the WindowAdapter class implements this interface by defining each of its methods, as a stubs.
Thus we can write in a JFrame method addWindowListener new WindowAdapter ; Of course, because every method in this class does nothing, we have added no new interesting behavior to the JFrame with this method call. But now, let's define some interesting behavior when the window is closed.
We can define the following class. This class inherits all the stub methods from the WindowAdapter superclass, but it overrides the windowClosing method the code inside says that when the user clicks the terminate button on this window, print a message, and the entire program itself that created the window should terminate. Note that this class implements the WindowListener interface: we can specifically say it does, or as illlustrated above, not say it: Java knows that any subclass of a class that implements an interface also implements that interface, because at worst it just inherits all of the needed methods.
Given this class, we can write addWindowListener new Terminator ; to give the JFrame the new behavior that we want. Notice that we are defining this subclass just to construct one instance of it, to pass to the addWindowListener method. The difference between JPanel and JFrame is that the former refers to a space where different types of visual elements, for example, images, texts or figures and controls such as text fields, buttons, etc.
The latter, on the other hand, represents an independent window with its unique characteristics. Refers to a general container used to assemble a group of components in sync. It is a fairly simple component that generally does not have a graphical user interface GUI. However, you can have a GUI if it is laid out against an opaque background or contains a display border.
The JPanel container class is in the javax. The former improves the serviceability of the latter. The JPanel is a very simple and lightweight container that is a subclass of the java. JComponent class. The JComponent in turn is a subclass of the container. Consequently, several methods used for JPanel are derived from its superclasses.
Some of the examples of such methods include image observer, alignments, and accessibility. The JPanel allows you to place checkboxes, buttons, images, fields, labels and even texts on it. It is primarily defined as an area where you can place controls and visuals. To use a JPanel, you first need to create its object, which is done by calling a JPanel constructor.
It is the base or foundation container used for creating independent GUI applications. It appears and runs like a window such as a notification window or a warning window that normally pops up on computer screens. Just like JPanel, it is also part of the swing toolkit but its parent class is Java.
What makes JFrame better than Frame is that it provides the option for closing or hiding the window by using the setDefaultCloseOperation int method.
It possesses its constructors and methods which are used to place components like text fields, buttons, borders, title bar etc. Each feature has its unique syntax used for customisation. It has two sub-divisions, namely menu bar and content pane. The components of JFrame are known as contents and most of the contents are found in the content pane.
Besides, to add content in the JFrame, one needs to put it in the content pane. JFrame employs a method of windows listener that starts working whenever a person carries out operations like activating, closing, opening, minimizing or maximizing a window. It also employs a mouse listener so that the frame can react to the actions of the mouse.
A JFrame can place inside itself multiple frames and JPanels but all of them depend on the mainframe for their existence.
A large number of functions can be created for the JFrame by using not only the methods of Listeners but also the methods of get, set and add methods. JPanel vs JFrame. JPanel actually serves as a general purpose container. It is where more complex, or bigger operations, are usually put.
You can put many operations inside one panel. There are so many methods that can be used for JPanel, which it inherited from its super classes. The accessibility, alignments, and image observer, are some of its examples.
In JPanel, you can also put fields, labels, buttons, check boxes, and even images, and many other functions. It simply represents an area where you can put visuals and controls. In Java Programming, in order to create a panel, you need to invoke a constructor JPanel this creates a blank panel. It is opaque by default, but you can change its background color. You can also customize its components using the Layout Managers.
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