a beginner wanna knows something about this( )

[Fahad Golra]

I have started java a month ago. And I have a little concept of some basic C++. Now while studying classes I came across a method this()whose logic, I don't seem to pick up. Can anybody please

[Roy Ben Ami]

it makes sense since you come from c++ you wouldnt get that method.
java uses the this() method so u can call one constructor from another constructor.
you cant do that in c++ but it looks for exmaple like this:

 
public Foo(int i)
{
  System.out.println("cool"+i);
}
public Foo(int i,String x)
{
this(i);
System.out.println(x);
}
 

you get the idea?
you can call one constructor from another in the same class to save some code writing (if the constrcutors have a simliar code to be written).
this() without anything as parameter calls the empty constructor in the class.
just as a last note. this() must be the first line in the constructor you are using and you can't have super() with it.
[ April 29, 2002: Message edited by: Roy Ben Ami ]
[ April 29, 2002: Message edited by: Roy Ben Ami ]

[Khurram Ajmeri]

hello there
this() is used for constructor chaining
for example..if u want to call a single argument constructor from within a zero argument constructor.
class Tiger{
Tiger(){
this(6); //must be the first line of a
} //constructor!

Tiger(int i){
System.out.println("Tiger");
}
}

if u are still confuse please read the book.

[Jackie Wang]

Can anyone help me about and give me a short example about the difference between this() and super? thanks so much! =)
coz I am stil lconfused after reading the teh contructor call for this and super

[Jackie Wang]

I mean i still don't understand after reading some notes about the contructor call, it make me more confused

Originally posted by jackie Wang:

coz I am stil lconfused after reading the teh contructor call for this and super

[Marilyn de Queiroz]

"this" is for the same class.
"super" is for the class that the "this" class extends (inherits from), in other words, its "super" class.

[Jessica Sant]

the one major rule with this() and super() is that it has to be the FIRST statement in the constructor definition (if you're using it).
-- so because of that -- you can't use both this() and super() in the same definition.

[Jackie Wang]

thanks jessica and Marilyn for the prompt reply.
I really appreciated that.
Any simple example which can demonstrate the "super()"? Thanks so much

[Dirk Schreckmann]

class Base 
{
    public Base( String color ) 
    {
        System.out.println( "Base is " + color );
    }
}
 
class Sub extends Base 
{
    public Sub( String baseColor, String subColor ) 
    {
        super( baseColor );
        System.out.println( "Sub is " + subColor );
    }
}
 
public class StudySuper 
{
    public static void main( String[] args ) 
    {
        Sub sub = new Sub( "blue" , "red" );
    }
}

[Jessica Sant]

try running this blip of code -- with the println statements you'll be able to see the flow of operation:

public class MyMain
{
   public static void main( String[] args )
   {
      System.out.println( "Instantiate MySuper( \"blah\" );" );
      MySuper mySuper = new MySuper( "blah" );
      System.out.println( "" );
      System.out.println( "Instantiate MySub( \"stuff\" )" );
      MySub mySub = new MySub( "stuff" );
   }
}
class MySuper
{
   MySuper()
   {
      System.out.println( "MySuper() default constructor" );
   }
   MySuper( String s )
   {
      this();
      System.out.println( "MySuper( " + s + " )" );
   }
}
class MySub extends MySuper
{
   MySub( String s )
   {
      super(s);
      System.out.println( "MySub( " + s + " )" );
   }
}

Output:
Instantiate MySuper( "blah" );
MySuper() default constructor
MySuper( blah )
Instantiate MySub( "stuff" )
MySuper() default constructor
MySuper( stuff )
MySub( stuff )

[Jackie Wang]

thanks dirk and jessica. I got it now.
really appreciated that

[Fahad Golra]

Thank u all for making me understand this topic. Thank u all again

[Dirk Schreckmann]

As if [fill in some saying], here's a link to part of Sun's java tutorial that discusses this and super a bit: http://java.sun.com/docs/books/tutorial/java/javaOO/methodbody.html