basic java

[vijay24805]

hi!!!! every one

my doubt is!!!!

wats the use of wrapper classes in java???

why we neeed to change the primitives to objects!!!! cant we perform operatios and calling of function using primitives!!!!

pls explain with example!!!

[Supamagier]

What's your problem/question?

btw... cut down on the exclamation and question marks...

[vijay24805]

my doubt is!!!!

wats the use of wrapper classes in java???

[Eranga]

I can say it in this way.

The wrapper classes are normal classes that extend the Object superclass

Can you understand that.

[vijay24805]

That i know that it extends the Object class!!!!
I am asking wats the use of Wrapper classes!!! i we ar making primitive data types as wrapper!!!

[mrbharatmehta]

Hi vijay,

The concept of Wrapper classes is used to allow us to store primitives into collections. For example:
Suppose you wish to make a List of integers. In this you can use the corresponding wrapper class for integers i.e Integer to store the value of the your primitive integer.
<CODE>
List<Integer> vijayList= new ArrayList<Integer>();
</CODE>

Also wrapper classes can be used to parse primitive data values from a string . like

<CODE> int vijayInt = Integer.parseInt("123");</CODE>

I hope that suffice. For rest of the methods in the Wrapper classes you can refer to Java API documentation

[vijay24805]

thanks i have one more doubt!!!

import java.util.Scanner;
class ScanNext {
public static void main(String [] args) {
boolean b2, b;
int i;
String s, hits = " ";
Scanner s1 = new Scanner(args[0]);
Scanner s2 = new Scanner(args[0]);
while(b = s1.hasNext()) {
s = s1.next(); hits += "s";
}
while(b = s2.hasNext()) {
if (s2.hasNextInt()) {
i = s2.nextInt(); hits += "i";
} else if (s2.hasNextBoolean()) {
b2 = s2.nextBoolean(); hits += "b";
} else {
s2.next(); hits += "s2";
}
}
System.out.println("hits " + hits);
}
}


If this program is invoked with
% java ScanNext "1 true 34 hi"


it produces
hits ssssibis2

how this works!!!! how we got this as output!!! pls explain!!

[CJSLMAN]

Vijay... you really should learn to communicate correctly when writing in the forum:

• Stop putting so many exclamation marks (!!!) after your sentences. It seems like you are demanding attention and it could be misunderstood and people will get angry or just ignore you.
• ALso, give your variable names some meaning... s, s2, etc... doesn't mean much and is confusing. Try str1, str2, intg, bool, etc... or something like that for names.
• If I read your program correctly, it's working as you programed it. Try to debug it... just follow the your code and you will find out why you got that output (hint: look at what the while loops are doing)

Luck,
CJSL

[Eranga]

Thumbs up Chris for you. I really looking into about naming conventions of variables in that code. Really hard to get an idea what's going on. Chris I guess lots of members who are trying to give an answer, are not run the code. Just go through the code and try to find where the error is. I do that most of the time. So naming variable in meaningful way is must.

[vijay24805]

ya sure!!!!

[Mara]

many people have already asked to STOP PUTTING EXCLAMATION MARKS .. the variables you have named make it confusing to explain it

[Fubarable]

Agrees with others above. Vijay, could you tone it down a bit?

[vijay24805]

what is the use of making strings in java as immutable?

[vijay24805]

one more doubt ,why is String class in java marked as final?

[CJSLMAN]

Answers are probably in this link:
String (Java Platform SE 6)

Luck,
CJSL

[pbrockway2]

wrapper/final/immutable...

These questions are getting at Java (and I would guess other language) syntax and idiom (usage). I would recommend reading a textbook - or Wikipedia which is often good at supplying an overview.

Googleing it for you reveals Wrapper_class and Final_(Java). Both articles are full of references to allied topics. If nothing else they should provide you with some way of framing a specific question - whether some specific opinion of yours is correct, what the meaning of some specific assertion is etc.

[vijay24805]

What is serialization? can anyone give a good example to explain that?

[Eranga]

You are asking questions in a hurry. Did you read anything before ask questions like this? Just like this, you cannot learn Java anyway. You must read more about theories in Java and do some examples.

[CJSLMAN]

Yeah... asking and asking and absolutely no thanks for the answers so far. The OP's 'tude is quite demanding.

CJSL

[Rooneyz]

• If I read your program correctly, it's working as you programed it.

This one I ought to remember, simply genius ;)