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I want to decide the arithmetic operator at run time and calculate the result of the operands. Is there a way to achieve it? 

public static void main(String[] args) { String operator = args[0]; int num1 = 10; int num2 = 20; int result = num1 operator num2; System.out.println(result); }
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  • May be you can. But at this point you need to work with compiled bytecode. Commented Nov 27, 2013 at 6:00

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If you're using JDK 1.6 or above, you can use the built-in Javascript engine like this.

public static void main(String[] args) throws Exception{ ScriptEngineManager mgr = new ScriptEngineManager(); ScriptEngine engine = mgr.getEngineByName("JavaScript"); String oper = args[0]; int num1 = 10; int num2 = 20; String expr = num1 + oper + num2; System.out.println(engine.eval(expr)); }

Warning: As seen from this answer, it is probably not the best idea to use it. But this suited the requirement in your question the best and hence the answer.

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7 Comments

Yes this would work, but it's work mentioning that eval should probably never be used.
The OP want to use operator at runtime.
@Quirliom - Could you share a link with me on why it shouldn't be used? I would love to add a proper reference along with the warning.
@R.J From a Purely Java stance, it's entirely out of place to include an interpreted statement, but I like this question which does a reasonable job. Other than that, I really like this answer.
+1 for entirely unthinkable approach!
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You can read it in as a String or char and then use if statements to perform the operation, like so:

public static void main(String... args) { String operator = args[0]; int num1 = 10; int num2 = 20; int result = 0; if(operator.trim().equals("+")) { result = num1 + num2; } else if(operator.trim().equals("-")) { result = num1 - num2; } else if(operator.trim().equals("*")) { result = num1 * num2; } else if(operator.trim().equals("/")) { result = num1 / num2; } // More operations here... System.out.println(num1 + operator + num2 + "=" + result); }

I would suggest, however, using the double datatype over int for precision's sake.

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