IRC log for #friendlyjava, 2020-01-27

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All times shown according to UTC.

Time	Nick	Message
01:27		Jantz joined ##friendlyjava
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17:32	mr_lou	Ohoy
17:33	mr_lou	Reading from a text file, we do: thisLine = br.readLine();
17:33	mr_lou	But we can also do: while ((thisLine = br.readLine()) != null) { // do stuff }
17:34	mr_lou	Where can I read about that? I mean, the fact that putting an if statement in a paranthese in order to check if it worked?
17:34	mr_lou	Or whatever to call it. What's it called?
17:40	aditsu	that's a while statement
18:07	aditsu	mr_lou: the only "special" thing in there is using an assignment as an expression
18:08	mr_lou	I mean...... what's it called when you put a condition in paranthese, and can get out true or false or null?
18:08	mr_lou	if (value = read()) { Yes, a value was read}
18:08	mr_lou	instead of
18:09	mr_lou	value = read();
18:09	mr_lou	if (value) { Yes, a value was read}
18:09	aditsu	well, what I said, using an assignment as an expression (more specifically, using the result of an assignment)
18:10	aditsu	and if (value = read()) is only in parentheses because "if" requires parentheses
18:11	aditsu	also, you "can get out true or false or null" only from an expression of type Boolean
18:13	aditsu	and you can do this kind of thing without any condition or if or while statement
18:14	aditsu	e.g. a = (b = 3) + 2;
18:16	aditsu	ah, it can be called an "assignment expression"
20:06	mr_lou	Let's take BufferedReader.
20:06	mr_lou	It has readline()
20:07	mr_lou	readline() reads a line of text. But returns null if it's the end of stream.
20:07	mr_lou	So you do
20:07	mr_lou	String line = "";
20:07	mr_lou	while (line!=null) line = readline();
20:08	mr_lou	And this is where you instead can do
20:08	mr_lou	while ((line = readline())!=null)
20:08	mr_lou	Where does null come from here? Is it because readline() returns null, or is it because the expression returns null?
20:12	aditsu	both
20:12	aditsu	the expression can return null because it returns the result of readline()
20:17	mr_lou	Hm
20:17	mr_lou	int a = 4; System.out.println(a=7);
20:17	mr_lou	I thought something like that would maybe output "true" because it was succesful, or something.
20:17	mr_lou	But it outputs 7
20:18	mr_lou	Anyway.... break time.
20:18	aditsu	well, how can the statement "a=7" be considered successful?
20:19	aditsu	or not successful?
20:19	aditsu	you're just assigning the value 7
20:19	mr_lou	More of a generalization. If statements in a paranthese would return true or false depending on success or not, it would also apply to such simple things.
20:20	mr_lou	I think PHP returns true/false
20:20	aditsu	they would only return true or false if the result is a boolean
20:20	aditsu	7 is not boolean
20:20	mr_lou	I think PHP don't care.
20:20	mr_lou	Thought it might be the same with Java
20:20	aditsu	php probably casts non-zero to true and zero to false
20:21	aditsu	maybe non-null and null in a similar way
20:22	aditsu	but why are we talking about php?
20:22	mr_lou	Because Java returning null confused me because PHP returns false
20:25	aditsu	java can return null, false, 5, "foobar" or any possible value in the world, depending on what expression you are using
20:26	aditsu	and I bet the same is true for php
20:29	mr_lou	So it's just the return value. It's not the expression.
20:29	mr_lou	https://www.php.net/manual/en/function.fgets.php
20:29	mr_lou	PHP returns false, because fgets() returns false.
20:29	mr_lou	And Java returns null because readline() returns null.
20:30	mr_lou	Ok, bedtime.
20:30	mr_lou	G'nite.
20:30	aditsu	well, if you call readline() then it returns whatever readline() returns
20:30	aditsu	g'night

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