How to parse operator from a string in Java

Question

I want to parse an operator say "+" from the string "+" which i entered as command-line argument at run-time and then add two integers say 'a' and 'b'.

So how can i perform the above task?

if say i enter "10+20" in commandline then how can i get the answer as "30"? — Himanshu Aggarwal, Mar 03 '13 at 09:03

score 2 · Answer 1 · answered Mar 03 '13 at 08:51

2

If you are using Java 1.7, you can use a switch to test for each possible operator and then do the corresponding operation:

switch(operator){
    case("+"): result = a + b; break;
    case("-"): result = a - b; break;
}

For older versions of Java can be done using if statements.

answered Mar 03 '13 at 08:51

niculare

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Or `operator.charAt(0)` – Mordechai Mar 03 '13 at 08:55
if say i enter "10+20" in commandline then how can i get the answer as "30"? – Himanshu Aggarwal Mar 03 '13 at 08:57
That's another question. Why didn't you ask that? – JB Nizet Mar 03 '13 at 09:02
i thought to try it later on if i could get some hint on this one. – Himanshu Aggarwal Mar 03 '13 at 09:04

score 2 · Accepted Answer · answered Mar 03 '13 at 09:21

2

What nobody so far is telling you is that to recognize arithmetic expressions in general you need to use, or write, a parser. Have a look for the Shunting-yard algorithm, recursive descent expression parsing, etc.

answered Mar 03 '13 at 09:21

user207421

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ok. i would hav to explore it a little more than. – Himanshu Aggarwal Mar 03 '13 at 09:23

score 1 · Answer 3 · answered Mar 03 '13 at 08:49

1

if (string.equals("+")) {
    System.out.println("The result is " + (a + b));
}

answered Mar 03 '13 at 08:49

JB Nizet

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if say i enter "10+20" in commandline then how can i get the answer as "30"? – Himanshu Aggarwal Mar 03 '13 at 09:02

How to parse operator from a string in Java

3 Answers3