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Super-power compare method? <?>

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Join Date: Nov 2005

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Cudmore

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Junior Poster in Training

Super-power compare method? <?>

Feb 2nd, 2007

Hi! I'm looking to learn something today, and I have just the question.

In writing a recent program, I found no Java method suited to compare two byte arrays. Maybe the method exists, or maybe not. In any case, this is a learning expedition, and I came up with a simple method designed to compare arrays of values. SontEqual can be adapted to byte, short, char, int, long, etc, and deals with arrays of such values.

 Help with Code Tags 
 java Syntax (Toggle Plain Text) 
static boolean SontEqual (byte[] a, byte[] b) {
     // Compare two byte arrays
     // Method by Matthew Cudmore ^.^
     // ----------
     if (a == null || b == null) return (a == b);
     if (a.length != b.length) return false;
     // ----------
     for (int i = 0; i < a.length; i++)
          if (a[i] != b[i]) return false;
     // ----------
     return true;
}
static boolean SontEqual (byte[] a, byte[] b) {
     // Compare two byte arrays
     // Method by Matthew Cudmore ^.^
     // ----------
     if (a == null || b == null) return (a == b);
     if (a.length != b.length) return false;
     // ----------
     for (int i = 0; i < a.length; i++)
          if (a[i] != b[i]) return false;
     // ----------
     return true;
}

Now there is a question in mind: can a single method be adapted to represent all numerical primitive types? Or must a separate method be written for each primitive type of array? I'm sure I've seen something of the <?> nature (or whatever it was), and I think it can be done.. Maybe it's got something to do with C++ and not Java. In any case, thanks in advance! I'm about to research this myself, and will post any significant findings for validation.

Last edited by Cudmore; Feb 2nd, 2007 at 11:41 am. Reason: Spell checking

synchronized (theWorld) { System.out.println ("It's all mine..."); }
How many people have code in their Sigs?

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jwenting

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duckman

Re: Super-power compare method? <?>

Feb 2nd, 2007

first, never name methods starting with a capital letter. That should ONLY be done with classes (by convention, and a good one it is).

As to your question. For primitive types it's rather impossible because of the way generics in Java work (they work only with classes and interfaces).
For those though it's rather sillily easy (took me a while to get it to compile because of a stupid typo I didn't catch in the compiler errors, but the code itself is trivial).

 Help with Code Tags 
 Java Syntax (Toggle Plain Text) 
class SomeClass<T> {
	public <T> boolean compare(T[] a, T[] b) {
		for (int i = 0; i < a.length; i++) {
			if (!a[i].equals(b[i])) {
				return false;
			}
		}
		return true;
	}
}
class SomeClass<T> {
	public <T> boolean compare(T[] a, T[] b) {
		for (int i = 0; i < a.length; i++) {
			if (!a[i].equals(b[i])) {
				return false;
			}
		}
		return true;
	}
}

I omitted part of your checks for brevity.

As people are clearly allowed to attack me but I'm not allowed to defend myself, I no longer post to this site.

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Join Date: Nov 2005

Posts: 74

Reputation: Cudmore is an unknown quantity at this point

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Cudmore

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Junior Poster in Training

Re: Super-power compare method? <?>

Feb 2nd, 2007

:o I noticed that little capital after posting.. Just didn't change it. Please excuse any naive stylistic choices, as I'm not yet completely accustomed to "convention".

And I did stumble upon the Java lesson about Generics here:
http://java.sun.com/docs/books/tutor...ics/index.html

No idea how I found it, because I didn't know what to look for, but now I think I understand this.

Generics work well in source code. However, "type erasure" occurs when compiled, so even if you were to work with Objects and not primitives, you couldn't have a single compiled method represent all possible class types. For deployed libraries, the source would have to be deployed (which is fine) and the generics would be worked out during compilation.

Kay, so I've learned: It's not possible for a single sontEqual method to represent all numerical primitive types. The method would need to be overridden for each supported type if it were to be deployed in a compiled library.

Last edited by Cudmore; Feb 2nd, 2007 at 4:43 pm. Reason: trying to be perfect

synchronized (theWorld) { System.out.println ("It's all mine..."); }
How many people have code in their Sigs?

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Join Date: Nov 2004

Posts: 6,143

Reputation: jwenting is just really nice

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jwenting

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duckman

Re: Super-power compare method? <?>

Feb 3rd, 2007

Yes, the binding is determined at compile time. But that hardly matters in practice, unless you're trying to write a program that's so generic that you don't know even a common basetype at that moment and have no choice but to pass in Object everywhere (at which point generics no longer make sense and you could just as well use Object as the parameter type everywhere).

As people are clearly allowed to attack me but I'm not allowed to defend myself, I no longer post to this site.