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The Container class holds the methods for grouping the components together, laying out the components inside it, and dealing with events occurring within it. Because Container is an abstract class, you never see a pure Container object; you only see subclasses that add specific behaviors to a generic container.
You can't just access foo as a direct reference if foo is abstract. If you can, design your interface such that it hides these details. It uses a copy semantic that calls the underlying clone on the stored object to make a deep copy. This is at least not worse than the original intent to store everything by value. The wrapper behavior is really up to what suits your needs.
Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Collectives on Stack Overflow. Learn more. Asked 7 years, 5 months ago. Active 3 years, 3 months ago. Viewed 8k times. For example I may want to be able to print both subclasses, simple feature, right?
Improve this question. Community Bot 1 1 1 silver badge. Herbert Herbert 4, 4 4 gold badges 38 38 silver badges 63 63 bronze badges. If possible, could you fork-amend the example with he least amount of extra code such that the behavior is defined?
Because I think that is not the main point of my code : I see you did so, thanx! Slicing is a bad name for a conversion. It took your moo , and made foo from it that is no longer a moo. If an event happens within a child component of a Panel , the target of the event is the child component, not the Panel.
There's one exception to this rule: if a component uses the LightweightPeer new to Java 1. With Java 1. The fact that the component is within a Panel has no relevance. The Insets class provides a way to encapsulate the layout margins of the four different sides of a container. The class helps in laying out containers. The Container can retrieve their values through the getInsets method, then analyze the settings to position components.
The different inset values are measured in pixels. The space reserved by insets can still be used for drawing directly within paint. Also, if the LayoutManager associated with the container does not look at the insets, the request will be completely ignored. This variable contains the border width in pixels for the left edge of a container. This variable contains the border width in pixels for the right edge of a container.
The constructor creates an Insets object with top , left , bottom , and right being the size of the insets in pixels. If this object was the return object from the getInsets method of a container, these values represent the size of a border inside that container. The clone method creates a clone of the Insets so the same Insets object can be associated with multiple containers.
The equals method defines equality for insets. Two Insets objects are equal if the four settings for the different values are equal. The toString method of Insets returns the current settings. Using the new Insets 10, 20, 30, 40 constructor, the results would be:.
The following source code demonstrates the use of insets within an applet's Panel. The applet displays a button that takes up the entire area of the Panel , less the insets, then draws a rectangle around that area. This is shown visually in Figure The example demonstrates that if you add components to a container, the LayoutManager deals with the insets for you in positioning them.
But if you are drawing directly to the Panel , you must look at the insets if you want to avoid the requested area within the container.
To change the applet's insets from the default, we override the insets method to return a new Insets object, with the new values.
A Window is a top-level display area that exists outside the browser or applet area you are working in. It has no adornments, such as the borders, window title, or menu bar that a typical window manager might provide. A Frame is a subclass of Window that adds these parts borders, window title.
Normally you will work with the children of Window and not Window directly. However, you might use a Window to create your own pop-up menu or some other GUI component that requires its own window and isn't provided by AWT.
This technique isn't as necessary in Java 1. There is one public constructor for Window. It has one parameter, which specifies the parent of the Window. When the parent is minimized, so is the Window. In an application, you must therefore create a Frame before you can create a Window ; this isn't much of an inconvenience since you usually need a Frame in which to build your user interface.
In an applet, you often do not have access to a Frame to use as the parent, so you can pass null as the argument. Figure shows a simple Window on the left. Notice that there are no borders or window management adornments present. The Window on the right was created by an applet loaded over the network. Notice the warning message you get in the status bar at the bottom of the screen. This is to warn users that the Window was created by an applet that comes from an untrusted source, and you can't necessarily trust it to do what it says.
The warning is particularly appropriate for windows, since a user can't necessarily tell whether a window was created by an applet or any other application. It is therefore possible to write applets that mimic windows from well-known applications, to trick the user into giving away passwords, credit card numbers, or other sensitive information. This is one way to create a Dialog , as we shall see. By repeatedly calling getParent until there are no more parents, you can discover an applet's top-level parent, which should be the browser's Frame.
Example contains the code you would write to do this. You should then check the return value to see if you got a Frame or null. This code is completely nonportable, but you may happen to be in an environment where it works. A handful of methods assist with the appearance of the Window. The pack method resizes the Window to the preferred size of the components it contains and validates the Window.
The show method displays the Window. When a Window is initially created it is hidden. If the window is already showing when this method is called, it calls toFront to bring the window to the foreground. To hide the window, just call the hide method of Component. After you show a window, it is validated for you. The dispose method releases the resources of the Window by hiding it and removing its peer.
The toFront method brings the Window to the foreground of the display. This is automatically called if you call show and the Window is already shown. The toBack method puts the Window in the background of the display.
The isShowing method returns true if the Window is visible on the screen. The getToolkit method returns the current Toolkit of the window. The Toolkit provides you with information about the native platform. This will allow you to size the Window based upon the current screen resolution and get images for an application.
See Section 6. The getLocale method retrieves the current Locale of the window, if it has one. Using a Locale allows you to write programs that can adapt themselves to different languages and different regional variants. If no Locale has been set, getLocale returns the default Locale. The default Locale has a user language of English and no region. To change the default Locale , set the system properties user. The getWarningString method returns null or a string that is displayed on the bottom of insecure Window instances.
If the SecurityManager says that toplevel windows do not get a warning message, this method returns null. However, Java allows the user to change the warning by setting the system property awt. Netscape Navigator and Internet Explorer do not allow the warning message to be changed. Netscape Navigator's current V3. The getFocusOwner method allows you to ask the Window which of its components currently has the input focus. This is useful if you are cutting and pasting from the system clipboard; asking who has the input focus tells you where to put the data you get from the clipboard.
The system clipboard is covered in Chapter 16 , Data Transfer. If no component in the Window has the focus, getFocusOwner returns null. The addNotify method creates the Window peer. This is automatically done when you call the show method of the Window. Then you can do everything you need to with the information about the newly created peer. If an event occurs within a child component of a Window , the target of the event is the child component, not the Window.
In addition to the Component events, five events are specific to windows, none of which are passed on by the window's peer. These events happen at the Frame and Dialog level. The default event handler, handleEvent , doesn't call a convenience method to handle any of these events. If you want to work with them, you must override handleEvent. The postEvent method tells the Window to deal with Event e. It calls the handleEvent method, which returns true if somebody handled e and false if no one handles it.
This method, which overrides Component. With the 1. These methods register listeners and let the Window component inspect its own events. The addWindowListener method registers listener as an object interested in being notified when an WindowEvent passes through the EventQueue with this Window as its target.
When such an event occurs, one of the methods in the WindowListener interface is called. The removeWindowListener method removes listener as an interested listener. When you subclass Window , overriding processEvent allows you to process all events yourself, before sending them to any listeners.
In a way, overriding processEvent is like overriding handleEvent using the 1. When you subclass Window , overriding processWindowEvent allows you to process all events yourself, before sending them to any listeners. In a way, overriding processWindowEvent is like overriding handleEvent using the 1. If you override processWindowEvent , you must remember to call super. The Frame is a special type of Window that looks like other high level programs in your windowing environment.
It adds a MenuBar , window title, and window gadgets like resize, maximize, minimize, window menu to the basic Window object. The default layout manager for a Frame is BorderLayout.
The Frame class includes a number of constants used to specify cursors. These constants are left over from Java 1. Avoid using the Frame constants for new code. To see these cursors, refer to Figure To position the Frame on the screen, call Component. Since the Frame is initially hidden, you need to call the show method before the user sees the Frame. The getTitle method returns the current title for the Frame. If there is no title, this method returns null.
The getIconImage method returns the image used as the icon. Initially, this returns null. For some platforms, the method should not be used because the platform does not support the concept. The setIconImage method changes the image to display when the Frame is iconified to image. Not all platforms utilize this resource. The setMenuBar method changes the menu bar of the Frame to bar.
If bar is null , it removes the menu bar so that none is available. It is possible to have multiple menu bars based upon the context of the application. However, the same menu bar cannot appear on multiple frames and only one can appear at a time. The MenuBar class, and everything to do with menus, is covered in Chapter
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