[3614] in java-interest
Re: What's the deal with the variable *this*?
daemon@ATHENA.MIT.EDU (Arshad Noor - Technical Mgr - Sun )
Fri Nov 17 13:23:11 1995
Date: Fri, 17 Nov 1995 10:06:18 -0500
From: anoor@hedley.East.Sun.COM (Arshad Noor - Technical Mgr - Sun Integration)
To: java-interest@java.Eng.Sun.COM, michael@w3media.com
>From daemon@java Thu Nov 16 23:58 EST 1995
>Mime-Version: 1.0
>Date: Thu, 16 Nov 1995 17:26:38 -0700
>To: java-interest@java.Eng.Sun.COM
>From: michael@w3media.com (Michael Mehrle)
>Subject: What's the deal with the variable *this*?
>Precedence: bulk
>X-Info: To unsubscribe, send 'unsubscribe' to java-interest-request@java.sun.com
>
>Here's one question I originally e-mailed to John December (author of
>"Presenting Java"). If anyone else could answer this question, it would be
>_greatly_ appreciated!
>
>Congratulations to your book, it's a whole lot better than Java! (by Tim
>Ritchey). I'm a bloody beginner and your book helped a lot to master the
>"basicbasics" of Java. Hope that makes you feel better.;)
>
>I've got a question though: Here is a copy of your Segment class (please
>check out my comments, they're explained below):
>
>
>class Segment {
>
> private String thePlace = "Unknown";
> private int segmentNumber;
>
> Segment (int number) {
> segmentNumber = number; // *here's the bad boy, shouldn't it say:
> // this.segmentNumber = number; ?
> }
>
When a method refers to a variable inside the same class,
the "this" variable is implicit when it is used. The
only times you need to use "this" is when you need to use
it *explicitly* to prevent ambiguities.
For example, if your above code had been written as:
Class Segment {
private int segmentNumber;
Segment (int segmentNumber) {
this.segmentNumber = segmentNumber;
}
the "this" is required to prevent confusing the compiler.
================================================================================
Arshad Noor 400 Atrium Drive
Technical Manager Somerset NJ 08873
Sun Integration Voice: (908) 302-3822
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================================================================================
> Segment(int number, String aPlace) {
> this(number);
> thePlace = aPlace; // also here: this.thePlace = aPlace; ?
> }
>
> public void header() {
> System.out.println("Segment #" + segmentNumber + " " + thePlace);
> }
>
> public void action() { }
>
> public void cut() {
> System.out.println("---------------");
> }
>}
>
>Saw the remarks above? So this should apply to the subclass also then:
>
>class Dialogue extends Segment {
>
> private Person personA;
> private Person personB;
>
> Dialogue (int number) {
> super(number);
> }
>
> Dialogue(int number, String aPlace) {
> super(number, aPlace);
> }
>
> Dialogue (int number, String aPlace,
> String actor1Name, String actor2Name) {
> this(number, aPlace);
> personA = new Person(actor1Name); // this.personA = new
>Person(actor1Name);?
> personB = new Person(actor2Name); // this.personA = new
>Person(actor1Name);?
> }
>
> public void action() {
> greetings();
> talk();
> wrapup();
> }
>
> .... more methods ...
> }
>}
>
>
>You might wonder *where* I took that from. The URL is:
>
>http://java.sun.com/whitePaper/java-whitepaper-5.html#HEADING5-23
>
>Are this specifications just make-up and optional? According to the
>description these variables are used to clarify which variable one is
>referring to. In
>the Segment method, *this.segmentNumber* would mean the *segmentNumber
>instance variable* of this object, rather than the SegmentNumber parameter
>to the Segment method.
>
>
>Please let me know if I'm totally off track, or if I was right.
>
>Your reader,
>
>Michael Mehrle
>--
>
>P.S. I will also post this message to comp.lang.java, so that everybody
>can enjoy your reply (no I don't mean that maliciously!)
>
>
>
> ||||
> o o
>____________OOOo___<>___oOOO_______________
> http://www.w3media.com/w3media
> michael@w3media.com
> Tel. 310.441.9599
> Fax 310.441.5919
>
>"One man's mundane and desperate existence
> is someone else's Technicolor."
> -Strange Days-
>
>
> ||||
> o o
>____________OOOo___<>___oOOO_______________
> http://www.w3media.com/w3media
> michael@w3media.com
> Tel. 310.441.9599
> Fax 310.441.5919
>
>"One man's mundane and desperate existence
> is someone else's Technicolor."
> -Strange Days-
>
>
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