CBSE Class 12 Informatics Practices Notes Chapter 13 Front-End Interface
1. Command Line Interface (CLI)
It is a type of human computer interface (i.e. a way for human to interact with computers) that relies only on textual input and output. That is the entire display screen on the current active portion of it, shows only characters (and no images) and input is usually performed entirely with a keyboard.
The CLI gets its name from the fact that it is an interface, which contains command lines. A command line is a space on the display screen in which commands (i.e. instructions telling a computer to do something) are typed by the user.
e.g. The most familiar example of a CLI used by many people is MS-DOS.
2. Graphical User Interface (GUI)
It is a type of front-end user interface in which user interacts with computer using windows, icons, menus and other graphical components, which can be manipulated by a mouse or any other device and a limited use of keyboard.
A window is a (usually) rectangular portion of the monitor screen that can display its contents (e.g. a program, icons, a text file or an image) seemingly independently of the rest of the display screen. A major feature of GUI is the ability for multiple windows to be opened simultaneously. Each window can display different application or file (e.g. text, image or spreadsheet files) that have been opened/created with a single application,
Advantages of GUI
A major advantage of GUI is that it makes computer operation more intuitive and thus easier to learn and use e.g. it is much easier for a new user to move a file from one directory to another by dragging an icon with the mouse rather by having to remember and type seemingly arcane commands to accomplish the same task.
Adding to this intuitiveness of operation is the fact that GUIs generally provide users with immediate, visual feedback about the effect of each action e.g. when the user deletes an icon representing a file, the icon immediately disappears, confirming that the file has been deleted. This contrasts with the situation for a CLI, in which the user types a delete command alongwith the name of the file to be deleted. But does not receive automatic feedback indicating that the file has actually been removed.
In addition, GUIs allow users to take full advantage of the powerful multi-tasking capabilities of modern operating systems, by allowing such multiple programs and/or instances to be displayed simultaneously. The result is a large increase in the flexibility of computer use and a consequent rise in user productivity. Building the Front-End using NetBeans IDE
- Choose File → New Project. Alternatively, you can click the New Project icon in the IDE toolbar.
- In the categories Pane, select the Java node. In the Projects Pane, choose Java Application. Click Next.
- Type in the Project Name field and specify a path, e.g. in your home directory, as the project location.
- Select (optional) the dedicated folder for storing libraries checkboxes and specify the location for the libraries folder. See Sharing Project Libraries for more information on this option.
- Deselect the create main class checkbox, if it is selected.
- Click Finish.
To proceed with building our interface, we need to create a Java container in which we will place the other required GUI components. In this step, we will create a container using the JFrame component. We will place the container in a new package, which will appear within the Source Packages node.
Contents of Front-End
Front-end interface have various graphical controls in GUI. These graphical controls are also called graphical objects. An object is a logical entity that an application displays or manipulate. These graphical objects have properties that can be changed and by changing these properties the user view changes. Front-end interface consider that all the contents should work in efficient and user friendly manner. In GUI based Java (Swing API) applications, you should always consider the swing components or control and their types.
Types of Swing Controls
The swing components or controls are classified into two categories:
Swing is the primary Java GUI widget toolkit. It is a part of Oracle’s Java Foundation Classes (JFC) an API for providing a Graphical User Interface (GUI) for Java programs.
Swing was developed to provide a more sophisticated set of GUI components than the earlier Abstract Window Toolkit (AWT). Swing provides a native look and feel that emulates the look and feel of several platforms and also supports a pluggable look and feel that allows applications to have a look and feel unrelated to the underlying platform. It has more powerful and flexible components than AWT.
In addition to familiar components such as buttons, checkboxes and labels, etc. Swing provides several advanced components such as tabbed panel, scroll panes, trees, tables and lists. Unlike AWT components, Swing components are not implemented by platform specific code. Instead they are written entirely in Java and therefore are platform independent. The term “lightweight” is used to describe an element.
A container is a special type of component that can hold other components, e.g. JFrame container. A container is also called a Parent Component, whereas the components contained in a container are called Child Component. Container can be categorised into the two types:
- Top-level Container These container can be displayed directly on the desktop or screen window. JFrame and JDialog are top-level container.
- Non-Top-level Container These container can be displayed with the context of another top-level container. These can be general-purpose or special-purpose container. JScrollPane is a non-top-level container.
Basic Swing Controls
Swing controls are basic building blocks of an application. Swing toolkit has a wide range of various control such as buttons, checkboxes, sliders, list boxes, etc. In this section of the tutorial, we will describe some useful controls.
- JList Control It is a control that displays a list of objects. It allows the user to select one or more items.
- JTextArea Control It is a multi-line text area that displays plain text. It is lightweight control for working with text. The control does not handle scrolling. For this task, we use JScrollPane control.
- JTextField Control It is a control which represents a textbox and it allows the displaying of only a single line of text.
- JRadioButton Control It is a way by which we can select only one button at any instance from a group of button.
- JCheckBox Control It consists of two states either ON or OFF. If the checkbox is clicked, it show by a tick mark in the box.
- JButton Control It generally represents a button that, when clicked by used, carries out a particular action. It is clicked by user to trigger a specific action.
- JComboBox Control It is like a drop-down box. It contains a textbox and drop-down menu. User can click a drop-down arrow and select an option from a list.
Features of Front-End
The features of front-end can be divided into two categories described below:
1. Display Features
Include all types of widgets, such as dialog boxes and other controls to enhance user-friendliness of the application. The highly effective front-ends are generally designed and share common characteristics.
We are discussing here:
- Conventional use of Icon To make an application effective, it is necessary to use of icon so that user can easily recognise their function. There are so many reserved icon for representing their functionality.
- Rare use of Audible Feedback Studies have shown that after frequent usage, the users become either ignorant of audible feedback or get irritated. Thus an effective front-end interface should avoid use of audible. It should be included where it can not be avoided.
- Use of conventionally Reserved Words There are so many reserved words those are used to develop an effective front-end interface like new is used to take new document. There are some reserved words given here ok, cancel, save, close, exit, help, etc.
- Use of controls In front-end interface, controls are the visible elements which are used to interact with the application. These controls are used for specific purpose. Some of common used controls are given here CheckBox, RadioButton, ListBox, Table, TextField, TextArea, etc.
- Use of visual feedback An effective front-end interface provides a visual feedback time to time. A visual feedback must be given, if any task is taking time to be completed, e.g. when we copy a file into hard disk, a dialog box appears showing estimated time to be completed and with a progress bar.
2. Functionality Features
Some common used functionality features are supported by an effective front-end are being listed here:
- Provides keyboard support An effective front-end provides keyboard support that user can easily select or work with menu items and controls while working. This feature helps to users who prefer to work with keyboard.
- Provides validation feature An effective front-end provides validation feature for performing a task in effective manner. This feature can be applied to a text field to check that value for it can not be blank or for it formatting.
- Security feature Security feature is used to authenticate user login by providing a visual screen that allows a limited number of login trials.
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