In c++ we could use macro as
#define check_and_log_warning(x) if (!(x)) {log_error(#x); cout<<__LINE__;}
I want to get values of a boolean expression and also use it as a string.
Getting the line number inside macro would be added benefit.
Can something like this macro be written in Java ?
I recently moved from c/c++ to java, so I am wondering could such thing be done in c++ without macro ?
Preprocessor is what I miss from C/C++ in Java. There are ways ..., but they are Java ways.
1/ Assertions:
http://docs.oracle.com/javase/7/docs/technotes/guides/language/assert.html
2/ Logs:
The one that I use is https://commons.apache.org/proper/commons-logging/
(over log4J or whatever you want)
To print line numbers in log messages, you can use something like:
int lineNo = Thread.currentThread().getStackTrace()[2].getLineNumber();
Edit:
Be warned: unlike __LINE__ in C++ getting the stack trace incurs a performance penalty. Be nice :)
There is no macro facility in Java.
You would be using a logging framework (of which there are plenty to choose from).
if (! theActualConditionNotJustX) myLogger.error("describe problem here");
The logging backend (if configured that way) makes sure to capture and display line numbers. There is some runtime cost for this, but it is usually negligable, especially where actual "errors" are involved (it can get a bit costly for trace-level logging).
Related
This question already has an answer here:
How to have placeholder for variable value in Java Text Block?
(1 answer)
Closed 2 years ago.
Just came across a new feature in Java 15 i.e. "TEXT BLOCKS". I can assume that a variable can be added inside a text block by concatenating with a "+" operator as below:
String html = """
<html>
<body>
<p>Hello, """+strA+"""</p>
</body>
</html>
""";
But are they providing any way so that we can add variables the way which is becoming popular among many other languages as below:
String html = """
<html>
<body>
<p>Hello, ${strA}</p>
</body>
</html>
""";
This question might sound silly but it may be useful in certain scenario.
Java 15 does not support interpolation directly within text blocks nor plain string literals.
The solution in Java 15 is to use String.formatted() method:
String html = """
<html>
<body>
<p>Hello, %s</p>
</body>
</html>
""".formatted(strA);
From the spec for text blocks:
Text blocks do not directly support string interpolation.
Interpolation may be considered in a future JEP.
"String interpolation" meaning
evaluating a string literal containing one or more placeholders,
yielding a result in which the placeholders are replaced with their
corresponding values
from Wikipedia
As stated above, maybe we'll get it in the future. Though it is difficult to say how they could possibly implement that without breaking backwards compatibility -- what happens if my string contains ${}, for example? The Java language designers rarely add anything that is likely to break backwards compatibility.
It seems to me that they would be better off either supporting it immediately, or never.
Maybe it would be possible with a new kind of text block. Rather than the delimiter being """, they could use ''' to denote a parameterized text block, for example.
As already discussed, this is not possible in JDK15 and you cannot change that fact.
But, I suppose you are trying to suggest a thing like this in C# language.
https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/tokens/interpolated
Although this is just a syntax sugar thing over string.Format() method in C# (which is a counterpart of String.format() in Java), apparently it is nice if we can have this in Java. This is an extension to the existing way of describing string literal in the language syntax, but of course this can be easily adapted onto text block specification as well.
If this is what you have in your mind, you can make a proposal to Java Community Process to expand Java Language Specification. This is very much lighter syntax/semantics enhancement than adding full-featured template engine in Java Compiler/Runtime specification, and it is possible that they would agree with you.
As user #Michael mentioned: No. 'they' (team Project Amber, who are implementing JEP 368) are not providing any way to interpolate the string in the text block.
Note that I somewhat doubt it'll ever happen. For starters, there is the backwards compatibility issue; any such attempt to introduce interpolation requires some marker so that any existing text blocks aren't all of a sudden going to change in what it means depending on which version of javac to invoke.
But more to the point, you yourself, asking the question, can't even come up with a valid example, which is perhaps indicative that this feature is less useful than it sounds. It looks like you came up with a valid use case, but that's not actually true: If what you wrote would compile and work, then you just wrote a webapp with a rather serious XSS security leak in it!
The point is, what you really want is 'templating', and whilst templating sounds real simple (just evaluate this expression then shove the result into the string right where I typed the expression, please!) - it just isn't. Escaping is a large reason for that. But you can't blanket-apply the rule that ${strA} in a text block means: Evaluate expression strA, then HTML escape that, then put it in, for two reasons: Who says that the string you're interpolating things into is HTML and not, say, JSON or TOML or CSV or whatnot, and who says that the interpolation I desire requires escaping in the first place? What if I want to dynamically inject <em> or not, and I don't want this to turn into <em>?
Either we update the langspec to cater to all these cases and now we're inventing an entire templating system and shoving that into a lang spec which seems like a job far better suited to a dedicated library, or we don't, and the feature seems quite useful but is in fact niche: Either you rarely use it, or you have security and other bugs all over your code base - any lang feature that invites abuse is, and I'd hope one would agree with me on this - not a great feature.
Yes, many languages have this, but the current folks who get to decide what java language features make it into future versions of the language seem to be in the phase that they acknowledge such features exist and will learn lessons from it, but won't add features to java 'just because all these other languages all have it' - some thought and use cases are always considered first, and any such analysis of interpolation on string literals probably leads to: "Eh, probably not a worthwhile addition to the language".
div(1, sum(1, exp(sum(div(5, product(100, .1)), -5))))
I'm using this in a Solr query, and want to verify that it is the same as :
Where x is 5.
Is this language Java?
If it is, why am I getting this output here:
http://ideone.com/LWYWtU
If it isn't, what language is this and how do I test it?
Thanks in advance for your help.
EDIT: To add more of the surrounding code, here is the full boost value I'm sending to Solr:
if(exists(query({!frange l=0 u=60 v=product(geodist(),0.621371)})),div(1, sum(1, exp(sum(div(product(5), product(100, .1)), -5)))),0)
The reason I think it might be Java is because in the docs, it says Most Java Math functions are now supported, including: and then lists the math functions I ended up using for code.
Solr is Java, but that's not relevant since this is a set of functions that Solr parses and evaluate itself (and not related to Java, except that the backing functions are implemented in Java).
As far as I can say from what you've mapped the functions correctly, as long as the 5 in product(5) is the same as X. You shouldn't need product there, as the value can be included in div directly as far as I can see.
A way to validate it would be to use debugQuery in Solr and see what the value is evaluated as, and then compare it to your own value. Remember that floating point evaluation can introduce a few uncertanities.
I'm trying to port a Matlab code to Java and C++.
It's quite straightforward however I find a function that is more than simple operations, it numerically evaluates integral:
lungh=quad('normpp',0,1,[],[],x1,x2,x3,x4,x5,x6,x7,y1,y2,y3,y4,y5,y6,y7);
Here x1,...,x8 and y1,...,y7 are simple numbers.
First of all, how do this parameters are interpreted? How does this function work?
I think that 0 and 1 are the bounds of the integral...but what about the others?? Especially 'normpp' and []?
I read the quad help but I didn't understand how it works with such an amount of parameters.
The second problem is: Do exist a java and a C++ libraries that offer these function?
I would prefer to do it directly in Java and C++ without calling Matlab.
Thanks!
In C there is a very nice library : The Gnu Scientific Library (GSL).
Here is a link to the Numerical integration page of the GSL :
GSL
The use of this library in a C++ project is straight forward.
I think the function gsl_integration_qag is a good choice to replace the matlab quad function.
Are there any Java API(s) which will provide plural form of English words (e.g. cacti for cactus)?
Check Evo Inflector which implements English pluralization algorithm based on Damian Conway paper "An Algorithmic Approach to English Pluralization".
The library is tested against data from Wiktionary and reports 100% success rate for 1000 most used English words and 70% success rate for all the words listed in Wiktionary.
If you want even more accuracy you can take Wiktionary dump and parse it to create the database of singular to plural mappings. Take into account that due to the open nature of Wiktionary some data there might by incorrect.
Example Usage:
English.plural("Facility", 1)); // == "Facility"
English.plural("Facility", 2)); // == "Facilities"
jibx-tools provides a convenient pluralizer/depluralizer.
Groovy test:
NameConverter nameTools = new DefaultNameConverter();
assert nameTools.depluralize("apples") == "apple"
nameTools.pluralize("apple") == "apples"
I know there is simple pluralize() function in Ruby on Rails, maybe you could get that through JRuby. The problem really isn't easy, I saw pages of rules on how to pluralize and it wasn't even complete. Some rules are not algorithmic - they depend on stem origin etc. which isn't easily obtained. So you have to decide how perfect you want to be.
considering java, have a look at modeshapes Inflector-Class as member of the package org.modeshape.common.text. Or google for "inflector" and "randall hauch".
Its hard to find this kind of API. rather you need to find out some websservice which can serve your purpose. Check this. I am not sure if this can help you..
(I tried to put word cacti and got cactus somewhere in the response).
If you can harness javascript, I created a lightweight (7.19 KB) javascript for this. Or you could port my script over to Java. Very easy to use:
pluralizer.run('goose') --> 'geese'
pluralizer.run('deer') --> 'deer'
pluralizer.run('can') --> 'cans'
https://github.com/rhroyston/pluralizer-js
BTW: It looks like cacti to cactus is a super special conversion (most ppl are going to say '1 cactus' anyway). Easy to add that if you want to. The source code is easy to read / update.
Wolfram|Alpha return a list of inflection forms for a given word.
See this as an example:
http://www.wolframalpha.com/input/?i=word+cactus+inflected+forms
And here is their API:
http://products.wolframalpha.com/api/
I'm wondering if util code already exists to implement some/all of *NIX tail. I'd like to copy the last n lines of some file/reader to another file/reader, etc.
This seems like a good bet: Tailer Library. This implementation is based on it, but isn't the same. Neither implement a lookback to get the last 100 lines though. :(
You could take a look at this tail implementation in one of Heritrix's utility classes. I didn't write it but I wrote the code that uses it, works correctly as far as I can tell.
This is a UI app - you can look at the source though to see what it does (basically some threading & IO). Follow.
The "last n lines" is quite tricky to do with potentially variable width encodings etc.
I wrote a reverse line iterator in C# in response to another SO question. The code is all there, although it uses iterator blocks which aren't available in C# - you'd probably be better off passing the desired size into the method and getting it to build a list. (You can then convert the yield return statements in my code into list.add() calls.) You'll need to use a Java Charset instead of Encoding of course, and their APIs are slightly different too. Finally, you'll need to reverse the list when you're done.
This is all assuming you don't want to just read the whole file. If you don't mind doing that, you could use a circular buffer to keep "the last n lines at the moment", reading through until the end and returning the buffer afterwards. That would be much much simpler to implement, but will be much less efficient for very long files. It's easy to make that cope with any reader though, instead of just a few selected charsets over a stream (which my reverse iterator does).