How to Add Functionality to NetBeans GUI: Java Programming

Programmer can know, to add graphical components in a frame and how to set their properties. But doing much is not sufficient in java programming, because the graphical controls that you add to frame can’t do anything on their own.

In other words, they have the look but not any feel. To add feel i.e. functionality or behaviour to them, you must also know about something called events and listeners. The three major players that add functionality to GUI are:

• The Event: An event is an objects that gets generated when user does something such as mouse click, dragging, pressing a key on the keyboard etc.
• Source of the Event: The component where the event has occurred, is the source of the event. For example, if a user clicks (the Event) on a Submit button then the source of this event is Submit button.
• Event Listener: An event listener is attached to a component and contains the methods/functions that will be executed in response to an event. For example, if a user click on a button, then the buttons event listener will executed some code in response to this event.
  Listener Interface. An event Listener stores all the methods that it will implement in response to events, inside the listener interface. So, you can say that a listener interface stores all event-response-methods or event-handler methods of an event listener.

Commonly used Events and Listeners.

• ActionEvents: of type ActionListener used to gets activated when the user performs an action with a button or other components. Usually, a user invokes the button by clicking over it. However, the user can also invoke a button action tabbing to the button and pressing the Enter key.
• ItemEvent of type ItemListener used to gets activated when the selected item in a list control, such as a combo box or list box, is changed.
• AdjustmentEvent of type AdgustListener used to gets activated when the user drags or moves knob of a scroll bar.
• ChangeEvent of type ChangeListener used to gets active when the properties of a slider change.
• KeyEvents of type KeyListener used to gets activate when the user press a key on the keyboard. You can use this event to watch for specific keystrokes entered by the user.
• ListSelection of type ListSelectionListener used to get activated when an item is selected/deselected from list (JList).
• MouseEvent of type MouseEventListener used to gets activated when the user does something with the mouse, such as clicks one of the buttons, drags the mouse, or simply moves over another objects.
• FocusEvent of type FocusEventListener used to gets activated when a components receives or lose focus. Focus is ability to receive input, e.g., you can select from a list box only when it has focus, you can type in a text field only if it has focus.  

Each of the listeners listed above have multiple methods stored in their listener interfaces to respond to different type of events. You are armed with some basic knowledge of GUI functioning in Java so in further articles i will let you know about to create a GUI application using NetBeans.

How to Retrieve Records without Duplication of Values: SQL Programming

Redundancy is each second programmer’s problem in querying with sql programming. Sql programming provides some in-built keyword that may be used to remove this problem. The article shows syntax and use of this keyword with examples.

When there is a requirement to eliminate rows with duplicate values in a column, the DISTINCT keyword is used. The DISTINCT keyword eliminates the duplicate rows from the result set.

The syntax of the DISTINCT keyword is:

SELECT [ALL|DISTINCT] column_names
FROM table_name
WHERE search_condition

Where

• column_names: name of fields to be displayed in output.
• table_name: name of table from which records are to be retrieved.
• Search_condition: mostly used to filter the output.
• DISTINCT keyword specifies that only the records containing non-duplicated values in the specified column are displayed.

In a query that contains the DISTINCT keyword, you can specify more than one column name. In that case, the DISTINCT keyword is applied to all the columns that are there in the select list. You can specify DISTINCT only before the select list. The following SQL query retrieves all the Titles beginning with PR from the Employee table:

SELECT DISTINCT JobTitle FROM HumanResources.Employee WHERE JobTitle LIKE 'PR%'

Output: The result contains all the records of employee table having PR, the starting two characters. The query will display only the JobTitle field, as specified in the query.

How to Retrieve Records from Top of Table: SQL Programming

Sql Programming provides a specific keyword that enables programmer to retrieve records from the top of the table. Programmer can use the TOP keyword to retrieve only the first set of rows from the top of a table. This set of records can be either a number of records or a percent of rows that will be returned from a query result.

For example, you want to view the product details from the product table, where the product price is more than $50. There might be various records in the table, but you want to see only the top 10 records that satisfy the condition. In such a case, you can use the TOP keyword.

The syntax of using the TOP keyword in the SELECT statement is:

SELECT [TOP n{PERENT}] column_name [, column_name…]
FROM table_name
WHERE search_conditions
[ORDER BY [column_name [, column_name…]

Where

• n is the number of rows that you want to retrieve.
• If the PERCENT keyword is used, then ‘n’ percent of the rows are returned.
• If the SELECT statement including TOP has an ORDER BY clause, then the rows to be returned are selected after the ORDER BY clause has been applied.

The following SQL query retrieves the top three records from the Employee table where the HireDate should be greater than or equal to 1/1/2002 and less than or equal to 12/31/2005. Further, the record should be displayed in the ascending order based on the SickLeaveHours column:

SELECT TOP 3 *
FROM HumanResources.Employee
WHERE HIreDate >= '1/1/2002' AND HireDate <= '12/31/2005'
ORDER BY SickLeaveHours ASC

Output: The result from the above sql query will be only top three records after satisfying the given condition.

How to Retrieve Records to be Displayed in a Sequence: SQL Programming

We have discussed many situations in which programmer retrieve records based on a condition. The purpose of this clause in sql programming, is not to verify the result, but to sort the result set. Using this clause, programmer can sort the records either in ascending or descending order.

Programmer can use the ORDER BY clause in the SELECT statement to display the data in a specific order. The order may be ascending and descending, depend on the requirement of query result.

The Syntax of the ORDER BY clause:

SELECT select_list
FROM table_name
[ORDER BY order_by_expression [ASC|DESC]
[, order_by_expression [ASC|DESC]…]

Where

• Select_list: the list of field names to be displayed.
• Table_name: name of table from which records are to be retrieved.
• order_by_expression is the column name on which the sort is to be performed.
• ASC specifies that the values need to be sorted in ascending order.
• DESC specifies that the values need to be sorted in descending order.

Optionally, you can also specify multiple columns, if you want to sort the result set based on more than one column. For this, you need to specify the sequence of the sort columns in the ORDER BY clause.

The following SQL query retrieves the record from the Department table by setting ascending order on the Name column:

SELECT DepartmentID, Name FROM HumanResources.Department ORDER BY Name ASC

Output: in the output the records are sorted alphabetically in ascending order according to name as shown in the image.

Now try the same query with DESC keyword.

SELECT DepartmentID, Name FROM HumanResources.Department ORDER BY Name DESC

Output: in the output the records are sorted alphabetically in descending order according to name as shown in the image.

Note: If you do not specify the ASC or DESC keywords with the column name in the ORDER BY clause, the records are sorted in the ascending order.

How to Use Properties Window to Change Control’s attribute: Java Programming

The controls/objects that a programmer draw on frame/window have some properties associated with them. Each control have its own properties with some common to other controls, which NetBeans enables to change.

The Properties Window provides an easy way to set properties for all objects in a frame/window. To open the Properties Window (if it is not open), choose the Properties command from the Window menu. You may also press the shortcut key for it which is: Control + Shift + 7.

A property can be of any type such as integer, string etc. These can be set by either a simple textbox or a dropdown list. The whole thing is properties window consist of the following elements:

• Title box Displays the name of the object for which you can set properties.
• Properties list The left column under Properties Tab, displays all of the properties for the selected object. You can edit and view settings in the right column.

As in previous article we have name a control using inspector window, now the same thing can be done through this properties window in following simple steps.

• In the Properties window, from the Properties list, select the name of a property.
• Type in the right column, or click more to type or select the new property setting.

The below image shows the operation of name a control by properties window. The next article will cover up about some components, events and listeners mostly used in java programming.

What are Naming Conventions in NetBeans: Java Programming

Object Naming Conventions, the process of giving a name to the control, basically used to access a control in coding part of programming language. Java NetBeans IDE have its own rules, described in the article, to name a control while programming.

A control's name is one of its most important attributes because you literally refer to a control by its name whenever you want it to do something. Names are so important that every time you put a control on your form, NetBeans IDE automatically gives a name to it. If programmer add a jButton, NetBeans IDE names it jButton1; if you add a jTextField, it automatically named jTextField1.

However, naming controls like this, may be confusing. While naming controls, you need to take care of these things.

• Must begin with a letter.
• Must contain only letters, numbers, and the underscore character (_); punctuation characters and spaces are not allowed.
• Omit the initial letter "J" in object names and you may add its type at the end of it, like ReCalculateCheckBox for an object of class JCheckBox (not ReCalculateCheckBox!). It is just a recommendation, not a rule laid out by Java.

Friendly Names

When naming is a control, the first letter of the friendly name is generally uppercase. This make it easier to read the control’s name, because you can easily differentiate between the friendly name and the control’s abbreviation e.g. ReadonlyCheckBox.  

Name a control

To name a control in NetBeans, double click the control to be named in the Inspector window and type a new name.

Alternatively, you can right-click on the control’s name in Inspector window or the control itself in design space and select Change Variable Name………. command. The same process can be done through properties pane. Before you actually start working with controls, you should also know how to setup properties for a control and also about event and listeners. Later articles will describe these with examples.

Change name using Properties Window

How to Perform Actions on Window Controls In NetBeans: Java Programming

There are many controls in the palette tab of NetBeans IDE having specific properties of its own. Those controls can easily be added, resize and delete from the frame, while programming in java. This article have some steps to do these tasks in simple way.

To draw a control on Frame/Window in NetBeans

• Click the desire control’s icon on the Palette. (Say, for example, we want to draw a label. For this we shall first click at its icon on the palette.)
• Now drag it to desired location in your Frame/Window.
• Se the control that you selected, now appear on your frame/window.

When you can add controls to your frame, you might find strange behavior of IDE regarding component positioning and sizing. (This is because of Free Design layout manager.) In order to have full control on component's positioning and sizing, you need to know about Layout Managers. The layout of components on a frame (or panel) is controlled by a layout manager, which determines the final placement of each component. Layout Managers will be covered in next articles.

To Remove a Control from the Frame/window in NetBeans

• Select the control to be deleted, by clicking it. See, the controls appear selected, notice the rectangular boxes at corners and sides.
• Press Del (or Delete) key. The selected control gets removed.

Another way of removing a control is:

• Select it
• Right-click on it (i.e., after selecting click the right mouse-key).
• A context menu paper. Select delete command from it.

To Move/Resize a control in NetBeans

To move a control you have drawn, click the object in the middle and drag it to the new location. Now release the mouse button.
To resize a control, select it first and then use its sizing handle to resize it. That is, move the mouse pointer over sizing handles. The mouse pointer will change to double-headed arrow (↔). See the fig. Now drag the sizing handle to desired new position and control will be resized.

While adding, laying out and resizing controls on the frame, if you are not happy with the default behavior of rearranging/resizing of the control, then you may done one thing. Before you put any controls on the form, right click your frame in Design View and select Set Layout. From the sub menu that appears, select Absolute Layout.