i dun understand....

[Tabrez Muchhala]

hi i am a beginner in java(juz started abt a month) :roll: and i dun quite really the following question which was given by my lecturer.....can anyone please help me...
e)A class is named StringReverse is declared with a constructor that takes in an argument S of type string for initializing the private member variable name of type String. It shows the reverse string
Give the definition of the StringReverse class
Print the string in reverse

[Barry Gaunt]

Can you do this part?

A class is named StringReverse is declared with a constructor that takes in an argument S of type String for initializing the private member variable name of type String.

Try coding it and post it here.

[Tabrez Muchhala]

here is what i think....

class StringReverse{

private String name;
public StringReverse(String S) { name = S;}
System.out.println(" ReversrName: " + name);}

but i dun really understand wat the question wants....esp the Define part....

[Barry Gaunt]

Good. this part is what we need.

class StringReverse{
    private String name;
    public StringReverse(String S) { name = S;}
}  

Let's look at the next part of the requirement.
"It shows the reverse string". That's confusing.
Can you add to StringReverse a public method called reverse that takes no arguments and returns a String? For now have the method return the name member variable not reversed.

[Tabrez Muchhala]

hope i right in this part....

 class StringReverse{    
private String name;    
public StringReverse(String S) { name = S;}
public reverse(){return name;}  } 

thanks .....

[Barry Gaunt]

Great!

class StringReverse{    
    private String name;
    public StringReverse(String S) {
        name = S;
    }
    public String reverse(){
        return name;
    }
}   

Now add a public static void main member that takes a String array called args.
The main method creates a variable name of type StringReverse using the first argument passed into main. The main method then prints the value returned by calling the method reverse() on the name variable.
[ March 16, 2003: Message edited by: Barry Gaunt ]
[ March 16, 2003: Message edited by: Barry Gaunt ]

[Tabrez Muchhala]

i think i wrong and i dun know why or how..pls correct me....

 
class StringReverse{    
private String name;    
public StringReverse(String S) { name = S;}
public String reverse(){return name;} 
public static void main(String[] args)
name[] StringReverse = {reverse() }; //i dun get this part..  :(   
System.out.println(" Name: " + reverse()); } 

[ March 16, 2003: Message edited by: Barry Gaunt ]

[Barry Gaunt]

class StringReverse{    
    private String name;
    public StringReverse(String S) {
        name = S;
    }
    public String reverse(){
        return name;
    }
    public static void main( String[] args )
    {
        // make a StringReverse object from
        // the first argument
        // ( like in java StringReverse Tabz
 
        StringReverse name = new StringReverse( args[0] );
        // Print the reversed name
        System.out.println( name.reverse() );
    }
}     

How does that compile and run? We are not finished yet.
[ March 16, 2003: Message edited by: Barry Gaunt ]
[ March 16, 2003: Message edited by: Barry Gaunt ]

[Tabrez Muchhala]

i get three errors...

F:\j2sdk1.4.0_03\bin>javac StringReverse.java
StringReverse.java:4: invalid method declaration; return type required
        public reverse(){return name;}
               ^
StringReverse.java:4: cannot return a value from method whose result type is voi
d
        public reverse(){return name;}
                                ^
StringReverse.java:13: cannot resolve symbol
symbol  : method reverse  ()
location: class StringReverse
        System.out.println( name.reverse() );    }}
                                ^
3 errors
F:\j2sdk1.4.0_03\bin>   

[Barry Gaunt]

Yes, I found the bug. We have got to have:
public String reverse()
{
return name;
}
See it? Fix it and try it again.
Getting nearer!

[Tabrez Muchhala]

yeah!!! the code compiled w/o any errors.....but wheni ran the program, i got the following exception..

 F:\j2sdk1.4.0_03\bin>javac StringReverse.java
F:\j2sdk1.4.0_03\bin>java StringReverse
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException
        at StringReverse.main(StringReverse.java:11)
F:\j2sdk1.4.0_03\bin>
 

is it b'cause there is nothing to reverse yet(thts wat i think)Pls correct me if i am wrong.....

[Barry Gaunt]

Yes, try java StringReverse Tabz

[Tabrez Muchhala]

it does print Tabz... thanks...now if it is reversed, it should print zbaT ..rite??..how do i go about doing that???
is there any way that i can print the string backwards if it is what i have to do..
(btw..have u come across such a question like mine?)

[Barry Gaunt]

This is where it gets interesting. It would be great in the reverse method if we could just do:
return name.reverse();
but we can't.
Try it.

[Tabrez Muchhala]

yea..i do get the 'cannot resolve symbol' err..
so let me get this straight..there is no way that a string can be reversed in this manner....rite how come?
do u know what is meant by "give the definition of the ReverseString class" i mean how in the world do i define it when the question itself tells me what to do??(which also cannot be done i wish i could kill my lect!!)

[Barry Gaunt]

No, that's not necessary!
We have to change the String name into "something else", reverse it, and then change it back into a String again. The "something else" is a StringBuffer.
Here goes:
1. Make a StringBuffer from name:
new StringBuffer( name )
2. Reverse it "inside" the StringBuffer:
new StringBuffer( name ).reverse()
3. Change it back to a String again:
new StringBuffer( name ).reverse().toString()
So instead of
return name.reverse()
do
return new StringBuffer( name ).reverse().toString(); // put this into the reverse method
Try that. But I'm finished for today, I'll take a look at your post tomorrow morning (European time)

[Tabrez Muchhala]

i followed yr steps ....i got three errors...
i confused....here's the code

 class StringReverse{    
private String name;    
public StringReverse(String S) { name = S;}
public String reverse(){return new StringBuffer(name).reverse().toString();} 

public static void main(String[] args)
 {      // make a StringReverse object from       
 // the first argument        
// ( like in java StringReverse Tabz   
    
  
StringReverse name = new StringReverse( args[0] );
StringBuffer(name) = new Stringbuffer(name).reverse();
new StringBuffer(name).reverse().toString();      
  // Print the reversed name       
System.out.println( name.reverse() );    }}     

[Barry Gaunt]

Hey Tabz! You changed a bit too much!
Just the reverse method needs to be changed. You did that OK. All the other stuff stays the same.
Try it out now.

class StringReverse {    
    private String name;
    public StringReverse(String S) {
        name = S;
    }
    public String reverse(){
    return new StringBuffer(name).reverse().toString();
    }
    public static void main( String[] args )
    {
        // make a StringReverse object from
        // the first argument
        // ( like in java StringReverse Tabz
        StringReverse name = new StringReverse( args[0] );
        // Print the reversed name
        System.out.println( name.reverse() );
    }
} 

[Tabrez Muchhala]

U R GREAT!!

 F:\>cd j2sdk1.4.0_03
F:\j2sdk1.4.0_03>cd bin
F:\j2sdk1.4.0_03\bin>javac StringReverse.java
F:\j2sdk1.4.0_03\bin>java StringReverse YRRABUKNAHT
THANKUBARRY
F:\j2sdk1.4.0_03\bin> 

btw the question asks me for the definition of the StringReverse class....
this means tht i must state the way the code works..like how it uses Stringbuffer to manipulate the String...rite...or is it a bullsh*t question given to me???

[Barry Gaunt]

It could be a "mad scientist" research question. The lecturer perhaps wants you to find out that the String class has no reverse() method. That's because String objects can't be changed inside once they have been created.
StringBuffer objects can be changed inside. The "Tabz" inside a StringBuffer can be reversed.
That's what we did in your program. But remember we had to change it back to a String again. The new String had "zbaT" inside it. You are stuck with that new String object because you cannot change it.
You can do many things with Strings and StringBuffers. Check out the Application programming Interface Documentation. Or take a look at the free Sun Tutorial. Above all, don't run too fast. This stuff ain't easy, but it's when it gets clearer.
If you don't understand some of this, go ask that "mad scientist" lecturer of yours, I'm sure he's not so daft as you think.
Cheers - Barry
[ March 17, 2003: Message edited by: Barry Gaunt ]

[Tabrez Muchhala]

Thank You Barry for enlightening me with your knowledeg!!....u r GREAT!!!

[Yuan Tseng]

is anyone can help me ... i was trying to use 'sun
one studio 4' to run this program but i got this error messages: java.lang.ArrayIndexOutOfBoundsException
at StringReverse.main(Reverse.java:13)
Exception in thread "main"

please tell me how do i correct that?

and on java StringReverse YRRABUKNAHT
how do i set up a test data if i run this on 'sun one stdio 4'?
thanks,

[Barry Gaunt]

Yuan, the program will only work given a String argument to work on. I did not want to make it more complex than needed.
I do not have SunOne ( Forte for Java ?) but there must be some buttons to press or menus to select so that you can specify an argument list to the program.
A hint: if you are just starting out with java do not use an IDE. Use a good simple editor and use the DOS command window ( or Cygwin ). If you must use an IDE I recommend the free learning tool BlueJ you can get from http://www.bluej.org/
[ March 19, 2003: Message edited by: Barry Gaunt ]