Programming Forums > Application Development > Java

Arevos · Aug 4th, 2006, 2:16 AM

Quote:

Originally Posted by v0id

C++ got it!

It has operator overloading and multiple inheritance, but not mutable classes.

v0id · Aug 4th, 2006, 2:19 AM

Oh, I thought that, thanks.
I'm not that familiar with C++ yet. :o

Harakim · Aug 4th, 2006, 12:08 PM

Quote:

Originally Posted by Arevos

I'd say Java's error handling systems were about average, here. It doesn't really boast any advanced error prevention devices, such as the design by contract methodology found in Eiffel, or the NullPointerException prevention syntax found in Nice.

At a snail's pace! Improvements to Java seem glacial compared to most other languages (especially Java's main competitor; C#).

I must be confused about design by contract and NullPointer Exception prevention, because I thought it had both of those.

As for your last comment, I never really thought about that! But choosing C# as a language would not be as wise as choosing .NET as a platform.

Arevos · Aug 4th, 2006, 1:54 PM

Quote:

Originally Posted by Harakim

I must be confused about design by contract and NullPointer Exception prevention, because I thought it had both of those.

Not natively. There are some libraries around that can give Java some design by contract functionality, but it's not built into the language itself.

Eiffel allows developers to define preconditions and postconditions for functions, and class invariants for classes. A precondition validates function input, a postcondition output. A class invariant is a statement that is always true about a class. The idea behind this is that any fault in the program is caught as soon as possible.

The NullPointerException prevention in Nice is also rather interesting. In Java, any reference can be set to null. In Nice, only references with the ? prefix can be set to null:

(Toggle Plain Text)

?String foo = "Test";
String bar = foo;    // compiler error

But we can convert ?String to String with a explicit test:

(Toggle Plain Text)

?String foo = "Test";
if (foo != null) {
    String bar = foo;    // compiles okay
}

Nice also has similar requirements in place to prevent casting errors; objects must be explicitly verified that they have the correct type. Java does not have this error checking capability.

Incidentally, Nice also has pre- and postconditions, though not class invariants.

lectricpharaoh · Aug 4th, 2006, 6:10 PM

@Arevos: Semi-OT, but what is a mutable class, and where would it be used? By your comments about Java and C++ lacking this, I assume you mean something beyond a class with mutable members.

Harakim · Aug 5th, 2006, 9:10 PM

It does however have a class loader, which I imagine you could use in that respect. I guess that wouldn't be a very good solution in some cases.

DaWei · Aug 5th, 2006, 9:20 PM

Arevos · Aug 6th, 2006, 2:44 AM

Quote:

Originally Posted by lectricpharaoh

@Arevos: Semi-OT, but what is a mutable class, and where would it be used? By your comments about Java and C++ lacking this, I assume you mean something beyond a class with mutable members.

By "mutable class", I mean a class where everything that is set at the time the class is created (such as its name, methods and inherited base classes), can be altered at runtime.

For instance:

 python Syntax (Toggle Plain Text) 
>>> class Foobar:
...     def apply(self):
...         print "Foobar"
...
>>> Foobar
<class __main__.Foobar at 0xb7e1ee3c>
>>> Foobar.__name__ = "Barfoo"
>>> Foobar
<class __main__.Barfoo at 0xb7e1ee3c>
>>>
>>> Barfoo = Foobar
>>> del Foobar
>>> Barfoo
<class __main__.Barfoo at 0xb7e1ee3c>
>>>
>>> Barfoo().apply()
Foobar
>>>
>>> def apply(self):
...    print "Barfoo"
...
>>> Barfoo.apply = apply
>>> Barfoo().apply()
Barfoo
>>> class Foobar:
...     def apply(self):
...         print "Foobar"
...
>>> Foobar
<class __main__.Foobar at 0xb7e1ee3c>
>>> Foobar.__name__ = "Barfoo"
>>> Foobar
<class __main__.Barfoo at 0xb7e1ee3c>
>>>
>>> Barfoo = Foobar
>>> del Foobar
>>> Barfoo
<class __main__.Barfoo at 0xb7e1ee3c>
>>>
>>> Barfoo().apply()
Foobar
>>>
>>> def apply(self):
...    print "Barfoo"
...
>>> Barfoo.apply = apply
>>> Barfoo().apply()
Barfoo

Quote:

Originally Posted by Harakim

It does however have a class loader

In order to get similar functionality, you'd not only have to use the class loader, but have to resort to lots of dynamic bytecode generation. Even then, it's such a complicated way of doing things that there becomes little benefit to attempting it in Java.

Mutable classes are really a feature that only dynamically typed languages can have.

Dameon · Aug 6th, 2006, 11:55 AM

Mutable classes, methods as objects...I see few compelling reasons.

But multiple inheritance! Someday, hopefully.

Aug 4th, 2006, 2:19 AM	#12
v0id Hobbyist Programmer Join Date: Apr 2006 Posts: 155 Rep Power: 3	Oh, I thought that, thanks. I'm not that familiar with C++ yet. :o __________________ -- v0id

Aug 4th, 2006, 6:10 PM	#15
lectricpharaoh Caffeinated Neural Net Join Date: Jun 2005 Location: Dry west coast of Canada Posts: 1,034 Rep Power: 5	@Arevos: Semi-OT, but what is a mutable class, and where would it be used? By your comments about Java and C++ lacking this, I assume you mean something beyond a class with mutable members. __________________ And once again, Probability proves itself willing to sneak into a back alley and service Drama as would a copper-piece harlot. - Vaarsuvius, Order of the Stick

Aug 5th, 2006, 9:20 PM	#17
DaWei Resident Grouch Join Date: Jun 2005 Posts: 6,453 Rep Power: 10	__________________ Abstraction doesn't make it impossible to write bad code; it makes it possible to write superior code. Contributor's Corner: Grumpy on C++ Exceptions DaWei on Pointers

Aug 6th, 2006, 11:55 AM	#19
Dameon Troll Join Date: Apr 2005 Location: Texas Posts: 732 Rep Power: 4	Mutable classes, methods as objects...I see few compelling reasons. But multiple inheritance! Someday, hopefully. __________________ MD5(sig) = bcef75433db02e9ad9bf81d6f7c5c270

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Aug 5th, 2006, 9:10 PM	#16
Harakim Hobbyist Programmer Join Date: May 2006 Location: West Jordan, Utah, United States Posts: 176 Rep Power: 3	It does however have a class loader, which I imagine you could use in that respect. I guess that wouldn't be a very good solution in some cases.

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