Re: newbie lost in strings......
From: Carl Smotricz (carl.smotricz_at_t-online.de)
Date: 07/30/04
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Date: Fri, 30 Jul 2004 01:56:51 +0200
I'd like to take a crack at answering why byte goes to 127!
A byte (in the general, not the Java sense) is usually an 8 bit
quantity; the 8 bits can be thought of as representing the positive
integers from 0 (no bits set) to 255 (all 8 bits set).
Java, however, rules that all integral primitive types (byte, int and
long) shall hold *signed* values. This means one bit is used as a sign
bit, with the advantage that those (in the case of byte) 8 bits can now
hold negative numbers as well, but the magnitude is a bit less. Since
2's complement is used for the representation, the values actually go
from -128 to 127.
Hope that helps.
-Carl-
Grant Wagner wrote:
> Frances Del Rio wrote:
>
>
>>ok, I'm INCREDIBLY confused about the diff. types of variables/data, b/c
>>before only prog I had done was JavaScript (and a bit of Pearl/CGI..) of
>>course in java, unlike JavaScritp, you have to say WHAT TYPE of data a
>>variable is..
>>
>>in
>>http://java.sun.com/docs/books/tutorial/java/nutsandbolts/variables.html
>>they list the diff. types of variables:
>>
>> // integers
>> byte largestByte = Byte.MAX_VALUE;
>> short largestShort = Short.MAX_VALUE;
>> int largestInteger = Integer.MAX_VALUE;
>> long largestLong = Long.MAX_VALUE;
>>
>> // real numbers
>> float largestFloat = Float.MAX_VALUE;
>> double largestDouble = Double.MAX_VALUE;
>>
>> // other primitive types
>> char aChar = 'S';
>> boolean aBoolean = true;
>>
>>1) you say below that int and integer are two differnt types (??)
>>("int and double are simple data types. Integer and String are
>>objects.") ok, so 'string' is not a type of data but an object?? man...
>>so when we declare
>>
>> String str = "I like learning Java";
>>
>> this is not a variable but an object?? confusing...
>
>
> When you do String s = "A string"; you're declaring a variable s that holds a
> reference to a String object containing the sequence of characters 'A', ' ',
> 's', 't', 'r', 'i', 'n', and 'g'.
>
> When you do int i = 0; you're declaring a variable i that holds the integer
> value 0.
>
> When you do Integer i = new Integer(0); you're declaring a variable i that
> holds a reference to an Integer object which holds the integer value 0.
>
> In each case you're declaring (and initializing) a variable.
>
> In some cases, the variable holds a reference to an object. That object
> contains some (or many values of different types - which can be other objects
> or primitives).
>
> In some cases, the variable is one of the primitive types (byte, char, int,
> long, double, float, boolean) and contains the actual value of that type.
>
>
>>(not to speack of byte largestByte, etc... can't even begin to figure
>>this out... short largestShort.. largestInteger, etc... what is this,
>>pls??? Largest?? largest in the universe???
>
>
> Byte is a class, MAX_VALUE is a static final variable that contains the
> largest value that a Byte object can possibly hold. The reason Java includes
> this is that in the future MAX_VALUE may change. If you hard-coded 127
> everywhere and suddenly MAX_VALUE went down to 63 (this is extremely unlikely
> to happen, it's more likely to go up, actually it's much more likely to never
> change), then all your code would break because a Byte can't hold a value
> larger then 63.
>
> When you write code that manipulates primitive types, sometimes you need to
> know the maximum or minimum values these primitives (and their corresponding
> classes: Byte, Integer, Long, Float, Double, etc) can hold. It's much better
> to ask the class what these limits are instead of assuming they are what they
> were in some previous version of Java. That's what you're doing when you write
> Byte.MAX_VALUE. You're asking the Byte class to return the value stored within
> itself called MAX_VALUE. This value is the maximum value that can be stored in
> a primitive byte, or an object created from the Byte class.
>
>
>>this stuff returns
>>
>>The largest byte value is 127
>>The largest short value is 32767
>>The largest integer value is 2147483647
>>The largest long value is 9223372036854775807
>>The largest float value is 3.40282e+38
>>The largest double value is 1.79769e+308
>>The character S is upper case.
>>
>>'largest byte value is 127' I mean how do we get to 127?? 32767?? ok,
>>very confused, thank you again for your help.. Frances
>
>
> They "get to" those values because someone wrote:
>
> public final class Byte extends Number implements Comparable {
>
> /**
> * A constant holding the maximum value a <code>byte</code> can
> * have, 2<sup>7</sup>-1.
> */
> public static final byte MAX_VALUE = 127;
>
> etc, etc
>
> The authors of Java have declared a variable inside the Byte class. It's
> public, so everyone can see it, it's static (which means you can use
> Byte.MAX_VALUE to see it), it's final (so someone can't do Byte.MAX_VALUE = 0;
> /* haha I messed with your head! */) and it's of the primitive type byte. It's
> assigned the value 127.
>
> I think you need to go back to the basics and understand the difference
> between a variable (which is just a symbolic name that points at or contains
> something) with the actual value that variable contains. "Integer ii" and "int
> i" both declare variables. You're telling Java ii will contain a reference to
> an Integer object, and i will contain an integer value.
>
> --
> Grant Wagner <gwagner@agricoreunited.com>
> comp.lang.javascript FAQ - http://jibbering.com/faq
>
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