String Vs. StringBuffer Vs. StringBuilder

	String	StringBuffer	StringBuilder
Mutable	No	Yes	Yes
Synchronized	No	Yes	No
Serialized	Yes	Yes	Yes

When to use these classes?

String – When your text is not going to change
StringBuffer – When your text will be changed by multiple threads
StringBuilder – When your text will be changed by a single thread

Comparison between mutable and immutable objects

String is always considered an immutable class because String objects can't be changed. Usually the "+" or concatenation operator is used to add a character sequence to an existing String variable, but that does not mean its making alterations to the existing object. If you have a look at the example below first a String object is created and then it is concatenated with another String which eventually creates a new object for Str1 to refer to in the memory.

String str1 = "abc"; //1st Object

str1 = str1 + "d"; //2nd Object

The scenario is different for a StringBuffer or a StringBuilder. Once an object is created, it can be changed as many times as possible using methods like append(). If you look at the example below, 1st an object is created and later changes are made to the existing object in the memory using append method.

StringBuffer sbf1 = new StringBuffer("abc"); //1st Object
sbf1.append("d"); //appends "d" to the 1st Object

Author: Thiagu

Updating an existing Trans-SQL Job's interval programmatically

The title itself suggests that the topic about to be discussed now has very little thing to do with Java, but this is something that any Java programmer needs to know when they are working along with SQL Server database.

Let’s look at the scenario now, let’s say you have created a Trans-SQL JOB to run a particular process periodically, but you want to provide the feasibility for the users to change the frequency to run the Trans-SQL JOB from your Java application itself. Now how is that possible? Ya, that’s what we are about to explore now, how to change the frequency from the Java application itself.
First create a JDBC connection as shown below
Once you have created the Connection class, make use of it in the main class to establish the connection with the Database. Create a callable statement where you will call the SQL Server System stored procedure called “sp_update_schedule”. Take note that the parameters assigned below are mandatory parameters for the said Stored Procedure. If you look at the code below, the value of the “schedule_id” is assigned to “10” and “name” is assigned to “null”. This is because either 1 value only should be initialized for “sp_update_schedule” to identify the schedule need to be updated.
For further reference about “sp_update_schedule”, please refer to: http://msdn.microsoft.com/en-us/library/ms187354.aspx

Author: Thiagu

Build your very own Mouse Trap Application

This is a very simple yet interesting concept. I had been seeing such applications being developed right from school kids to working professionals using Microsoft technology for the past few years and wondered how to make it possible in Java. I was actually surprised to know that API’s for controlling mouse cursor had been there in Java since JDK 1.3. Well this shows that nothing is impossible in Java,.....Can anyone deny that...haha.

Now let’s move on exploring this concept step-by-step.

1. Create a simple User Interface as shown below with 1 JButton. The JButton will used with an action “(System.exit(0))” once the cursor gets trapped within the frame.
2. Use a MouseListener event on the JPanel and override the mouseExited() Method.
3. The”if” statement in the OnMouseExit event is used to check if the cursor has went beyond the geographical boundaries of the JFrame. (This validation is done because even if the mouse touches the JButton, it will invoke the JPanel’s OnMouseExit Event).
4. The next line after the “if” statement shows the usage of Robot API (An API used to control mouse and keyboard automatically. This API was introduced in JDK 1.3).
5. The Robot API’s moveMouse method will move the cursor according to the X and Y axis that we set. (Here I’ve used the centre point of the JFrame ) .

Author: Thiagu

Perform an Event when “Enter” key is pressed

For this month since I had very limited time to come up with a post, I thought of discussing about this common yet simple question that many newbie have in mind.

Let’s say I have a JTextField and a JTextArea and every time when I press the “ENTER” key on the JTextfield, I need to append the text from the JTextField to the JTextArea.

This is a very simple scenario and to accomplish this we have to make use of the “KeyAdapter Class (which implements the KeyListener Interface)” and “KeyEvent Class”.

Once the key “Enter” is pressed we need to perform the action, so at this point we need to make use of the “keyReleased(KeyEvent evt)” method from the adapter class and then check if the keycode is equals to “evt.VK_ENTER”. The code snippets are as below.

For further reference and study kindly refer to this link http://java.sun.com/docs/books/tutorial/uiswing/events/keylistener.html

Author: Thiagu

Enabling a Row or a Column Selection in JTable (SWING)

In this example I’m going to discuss about how to select one whole row or a column when a cell in a JTable is clicked. It’s not something hard, since it just requires 3 lines of code to be included. Follow the steps below to make it happen.
Steps:

1. Since we are just going to select one particular row or column in a JTable, the selection mode has to be set as Single selection using the constants in ListSelection Model Interface. E.g: jTable1.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
2. If row selection is to be enabled, set the row selection method as “true” and column selection method as “false”. Code snippet and output are as below.
   
   
3. If column selection is to be enabled, set the row selection method as “false” and column selection method as “true”. Code snippet and output are as below.

Author: Thiagu

Rendering ComboBox in a JTable (SWING)

Ever wondered how to make a cell in a JTable to render a JComboBox? This example will guide you on that. The scope of this tutorial does not have to be limited to combobox, the same concept applies in rendering other components in a JTable.

1. Create a JTable with two columns as shown below.
2. Create an inner class that implements TableCellRender as below
3. Set the particular column's renderer as the renderer class that you have created
4. Create a JComboBox variable with the necessary values and pass it as a parameter to the constructor of the DefaultCellEditor class
5. WALLA....there’s your combobox, right where you want it...

Author: Thiagu

Changing JLabel’s background during mouse over (SWING)

Let’s look at how to change the background colour of a JLabel (by default is transparent) when the mouse cursor moves over it.

1. Create a JLable as above on your application using Netbeans IDE
2. Include the code snippet below to change the background colour of the JLabel.

3. As you can see in the code, JLabel3.setOpaque(true) line is used because by default a JLable will have a “false” value for the Opaque which makes the background transparent.
4. Once the Opaque is set to true, change the background colour.

5. Select the mouse entered action, which provides an action when the cursor gets into the boundaries of the JLabel.
6. Include the code snippet below to change the colour of the JLabel during mouse over.

Results:

Before Mouse Over

After Mouse Over

Author: Thiagu