Thread: Why do we use the "this" keyword?

Hi guys,

I am studying for a test, and one of sections is on inheritance.

And I really don't understand how the "this" keyword works.

From what I have read, this just references the active variable/object.

So for example, why is "this" used in the below code?

Such as with this.pages = pages;
and with this.definitions = definitions;

/**
 
 * Words.java - Demonstrates the use of the super reference..
 
 *
 
 * @author Lewis/Loftus
 
 * @version 2nd ed.
 
 */
 
public class Words2
 
{
 
   //-----------------------------------------------------------------
 
   //  Instantiates a derived class and invokes its inherited and
 
   //  local methods.
 
   //-----------------------------------------------------------------
 
   public static void main ( String[] args )
 
   {
 
      Dictionary2 webster = new Dictionary2( 1500, 52500 );
 
 
 
      webster.pageMessage();
 
      webster.definitionMessage();
 
   }
 
}

/**
 
 * Book.java - represents a book.
 
 *
 
 * @author Lewis/Loftus
 
 * @version 2nd ed.
 
 */
 
public class Book2
 
{
 
	protected int pages;
 
 
 
	/**
 
	 * constructor
 
	 *
 
	 * @param int (pages)
 
	 */
 
	public Book2( int pages )
 
	{
 
		this.pages = pages;
 
 
 
	} // constructor
 
 
 
	/**
 
	 * pageMessage - prints a message concerning the pages of this book.
 
	 */
 
	public void pageMessage()
 
	{
 
		System.out.println( "Number of pages: " + pages );
 
 
 
	} // method pageMessage
 
 
 
} // class Book

/**
 
 * Dictionary2.java - represents a dictionary, which is a book
 
 *
 
 * @author Lewis/Loftus
 
 * @version 2nd ed.
 
 */
 
public class Dictionary2 extends Book2
 
{
 
	private int definitions;
 
 
 
	/**
 
	 * constructor
 
	 *
 
	 * @param int (pages)
 
	 * @param int (definitions)
 
	 */
 
	public Dictionary2( int pages, int definitions )
 
	{
 
		super( pages );
 
 
 
		this.definitions = definitions;
 
 
 
	} // constructor
 
 
 
	/**
 
	 * definitionMessage - prints a message using both local and inherited
 
	 * values
 
	 */
 
	public void definitionMessage()
 
	{
 
		System.out.println("Number of definitions: " + definitions);
 
		System.out.println("Definitions per page: " + definitions/pages);
 
 
 
	} // method definitionMessage
 
 
 
} // class Dictionary (extends Book2)

this references the 'current' object (see Using the this Keyword (The Java™ Tutorials > Learning the Java Language > Classes and Objects)). It is useful in many situations, one of which is in the code you posted. For example, imagine the following scenario

public Dictionary2( int pages, int definitions )
	{
		super( pages );
		definitions = definitions;//bad code design
	} // constructor

In the above example, the parameter definitions will be set to itself (a pretty useless line of code) while the object variable definitions never gets initialized as intended