IRC log for #friendlyjava, 2020-01-13

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18:35	Al_nz1	morning
18:35	Al_nz1	anyone about
18:37	Al_nz1	anyone able to help please with a question I think related to types : https://stackoverflow.com/questions/59721950/type-error-converting-jts-to-geojson-with-feature
18:44	aditsu	hi Al_nz1
18:46	aditsu	still there?
18:47	aditsu	you wrote "It does not accept a string", that is not true
18:48	aditsu	the problem is the return type is not org.wololo.geojson.Geometry
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18:48	aditsu	but rather org.locationtech.jts.geom.Geometry
18:55	Al_nz1	aditsu: is it?
18:56	aditsu	yeah, that's what I can see both in the javadoc and in your screenshot
18:56	aditsu	sorry, github source code not javadoc
18:56	Al_nz1	aditsu: I thought line 15 and 16, shows return read(json, null);
18:56	Al_nz1	is that not returning a json, null?
18:57	aditsu	no, json and null are arguments to a read method
18:57	aditsu	"returning a json, null" does not even make any sense
18:59	Al_nz1	aditsu: ok, lets break this down, and see where my understanding is wrong.
18:59	Al_nz1	public Geometry read(String json) {
18:59	aditsu	ok
19:00	Al_nz1	that means return a Geometry object, and take in as a paramter String json ?
19:00	aditsu	yes
19:00	Al_nz1	the next line :
19:00	Al_nz1	return read(json, null)
19:01	Al_nz1	that means the method retuns "read(json, null)" ?
19:01	aditsu	basically, yes
19:01	aditsu	not the string, but the result of calling the method
19:02	Al_nz1	aditsu: right, so what confuses me then, is the read method returns a result to itself when it returns read(json, null) ?
19:03	aditsu	first of all, there are 4 different read methods there
19:03	aditsu	you're looking at the first one
19:03	aditsu	and the first one is calling the second one
19:04	aditsu	if we could give them numbers, it would be something like: public Geometry read1(String json) { return read2(json, null); }
19:05	aditsu	are you familiar with method overloading?
19:09	Al_nz1	brb
19:11	Al_nz1	sorry back
19:12	Al_nz1	aditsu: not really, but I am happy to go away and read up on it.
19:12	aditsu	ok, it's basically multiple methods with the same name but different number or type of arguments
19:12	Al_nz1	i guess the take away point here, is that the return object I should look at is the one in the method declaration - not so much the return type?
19:12	Al_nz1	aditsu: ah ok
19:13	aditsu	the return object is found in the return statement, the return type is in the method declaration
19:13	Al_nz1	so if I am trying to get a jts.geom to a geojson string i dont need a reader, I need a writer?
19:13	aditsu	since the return object is the result of a method call in this case, its type will be the return type of the 2nd method
19:14	aditsu	then it is converted to the return type of the first method, which happens to be the same type
19:15	aditsu	hmm, I am not familiar with the library, but it's possible that you need a writer
19:15	Al_nz1	right.
19:15	Al_nz1	well the writer method at least returns what I want - which is a wololo.geojson object
19:17	aditsu	btw, is "wololo" an AOE reference? :p
19:18	Al_nz1	whats AOE?
19:18	aditsu	Age Of Empires, a game
19:18	aditsu	see https://knowyourmeme.com/memes/wololo
19:21	Al_nz1	aditsu: ahh, I see. I dont know
19:22	Al_nz1	sooo, I am trying the writer now:
19:22	Al_nz1	https://gist.github.com/bigalnz/ba1cb1286cde917391892cd43a6da5d9
19:22	Al_nz1	but on line 23
19:24	Al_nz1	it complains that Feature(org.wololo.geojson.geometry, Map<String, Object>) in Feature cannot be applied to org.locationtech.jts.geom.point
19:24	Al_nz1	so I need to go and wee what the new Feature needs
19:25	aditsu	that already says that it needs org.wololo.geojson.geometry for the first argument
19:27	Al_nz1	ok, I accept it says that, BUT if I didnt have the benefit of that error, I would go to the Feature class
19:27	Al_nz1	https://github.com/bjornharrtell/jts2geojson/blob/master/src/main/java/org/wololo/geojson/Feature.java
19:27	Al_nz1	to me it looks like a new Feature can accept Geometry and Map<String, Object>
19:28	Al_nz1	where in that Feature class however could I tell if Geometry is of type jts.geom or wololo.geom ?
19:28	aditsu	oh, first you can look at the imports, but in this case it doesn't import any Geometry
19:29	aditsu	then it must be in the same package as the Feature class
19:29	aditsu	classes in the same package can be accessed directly by name
19:33	Al_nz1	ahh, ok. makes sense
19:36	Al_nz1	so i am getting there I think
19:38	Al_nz1	if I try this https://gist.github.com/bigalnz/3ff012cb445179fead670292ebc6cad8 look at line 26
19:38	Al_nz1	I need to get my jts.geom.point into a org.wololo.geom.geometry
19:39	Al_nz1	so if i look at https://github.com/bjornharrtell/jts2geojson/tree/master/src/main/java/org/wololo/geojson
19:39	Al_nz1	do I need a GeometryFactory instance to do the conversion?
19:40	aditsu	I don't see any GeometryFactory there, but anyway, I don't know anything about that library
19:41	Al_nz1	sorry I mean GeoJsonFactory, it has a method that returns Geometry
19:41	aditsu	I have no idea if that helps you or not
19:42	aditsu	I just saw that org.wololo.geojson.Point extends Geometry, so maybe you're supposed to convert your Point to the other kind of Point?
19:43	Al_nz1	aditsu: exactly, but I am trying to work out how
19:43	aditsu	there should be some documentation for the library
19:44	Al_nz1	are classes that have "Factory" in the name usually used for conversion?
19:44	Al_nz1	this is all I could find : https://github.com/bjornharrtell/jts2geojson/blob/master/README.md
19:44	aditsu	not really, they are usually used for creating objects based on some kind of configuration
19:46	aditsu	but this one may be used for conversion
19:48	Al_nz1	well the introduction in the readme says : This Java library can convert JTS geometries to GeoJSON and back.
19:48	Al_nz1	so it can do it, but how is what I am trying to figure out
19:48	aditsu	I don't know what either of those things are :)
19:50	Al_nz1	well jts.geom is one type, wololo.geojson is another
19:50	aditsu	it looks like GeoJSONReader and GeoJSONWriter both have multiple convert methods
19:51	aditsu	try those
19:59	aditsu	oh wait, they're not public! I think you're supposed to just use read/write
20:00	Al_nz1	I did
20:00	Al_nz1	I have got that part of the converison ok
20:00	aditsu	I mean you can use read or write to convert your Point to the correct Geometry
20:01	aditsu	I think it's read
20:02	Al_nz1	this worked :
20:02	Al_nz1	GeoJSONWriter writer = new GeoJSONWriter();
20:02	Al_nz1	org.wololo.geojson.Geometry geom = writer.write(p);
20:02	Al_nz1	where p is a jts.geom
20:02	aditsu	oh ok
20:03	aditsu	guess I "read" that wrong :p
20:03	Al_nz1	aditsu: yeah I was getting the reader and writer methods around the wrong way - guess it depends on which was you are looking at the conversion
20:04	aditsu	those names are not very self-explanatory...
20:05	Al_nz1	brb - need to get coffee :-)
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20:57	Al_nz1	back
21:00	Al_nz1	aditsu: I like the name of this channel
21:01	Al_nz1	some of the regulars on #java are arrogant pricks
21:01	aditsu	me too :)
21:04	Al_nz1	where abouts in the world are you located
21:04	pdurbin	Boston
21:04	aditsu	I'm in Hong Kong
21:05	Al_nz1	ahh, its earlyt there!!!
21:05	aditsu	or late, depending on your perspective :p
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