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From: markspace <markspace@nospam.nospam>
Newsgroups: comp.lang.java.programmer
Subject: Re: The Assignment Principle
Date: Sun, 26 Jan 2014 14:27:13 -0800
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On 1/26/2014 12:17 PM, Stefan Ram wrote:
>    Also, it is
>    about values and not expressions, so that
>
> v = java.lang.Math.random();


Well, most often it is about expressions:

   a = 2;
   b = 1;
   v = a * a + b;
   System.out.println( v == 5 );

Had darn well better print 'true';

Math.random() is kind of an exception, as well as NaN, which has its own 
semantics for comparisons.

It's fair to point out that objects have states, and method invocation 
often returns different values based on their internal state.

   InputStream in = ...
   v = in.read();

Is going to return a different value for each invocation, generally 
speaking.

We're getting into the difference between traditional languages, which 
do have state, and functional languages, which try to avoid mutable 
state whenever possible.  Functional languages try to mimic the behavior 
of algebra and mathematics, so that's why they look a lot closer the 
mathematical formulas and properties you are used to from that field.

But Java isn't functional programming, and those properties you learned 
for algebra aren't going to always work here.  Thus, learning Java 
involves learning a new set of rules, not trying to make Java work like 
the other set of rules.