String a = "a*3";
a = a.replace("a","45");
// a contains 45*3
How do you I convert that to a DOUBLE which outputs 135.00 ??
Note : a can have any arthimetic operation... ( + , - , /)
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Does it have one operator at most? – Maljam Mar 21 '16 at 18:51
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a can have multiple operators... like a = "((a+3)*4)" – Gowtham Mar 21 '16 at 18:53
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1If division is a valid operation in this string, there's no guarantee the result will be an int. (Just putting that out there) – Mage Xy Mar 21 '16 at 18:54
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my bad. I changed INT to double – Gowtham Mar 21 '16 at 18:55
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2You can check out this question: http://stackoverflow.com/questions/3422673/evaluating-a-math-expression-given-in-string-form – Denis Mar 21 '16 at 18:55
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1Go see my answer to this post, it's essentially the same question: http://stackoverflow.com/questions/35984375/recursive-program-in-java/35984815#35984815 – Maljam Mar 21 '16 at 18:56
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There is a library called exp4j i.e. expression4j which has predefined method like python `eval` function. Check this out http://www.objecthunter.net/exp4j/ – Vighanesh Gursale Mar 21 '16 at 19:05
1 Answers
5
Simplest solution is to pass this off to Java's built in JavaScript engine.
public class Eval {
public static void main(String[] args) throws ScriptException {
ScriptEngine engine = new ScriptEngineManager().getEngineByExtension("js");
engine.put("a", 45);
Number val = (Number) engine.eval("a*3");
System.out.println(val.doubleValue());
}
}
AJNeufeld
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