Adding numbers within a string in java

Question

How do I add two numbers within one string?

I have:

String a = "(x+x)";
String lb = "2";

String b = a.replace("x", lb);

int c = ?

it outputs 2+2, how do I get it to add them together correctly into an integer?

What's the issue in using it as a integer itself? Instead of putting it in String and trying to convert it back to integer. — Pradeep Simha, Oct 10 '13 at 17:08
possible duplicate of [free Java library for evaluating math expressions](http://stackoverflow.com/questions/7258538/free-java-library-for-evaluating-math-expressions) — Luiggi Mendoza, Oct 10 '13 at 17:10
It almost sounds like OP might be trying to implement some sort of evaluator for arithmetic expressions, perhaps unintentionally. In his example, he is printing the string "(2+2)" and expecting it to print "4". He might also be confused about String and integer types, but I wanted to throw out another possible explanation in case someone wants to expand on it. — William Brendel, Oct 10 '13 at 17:12
`int lb = 2; System.out.println( "" + lb + "+" + lb ); System.out.println( lb+lb );` — clcto, Oct 10 '13 at 17:13

sushain97 · Accepted Answer · 2013-10-12T14:52:39.593

1

While you can use a Java library to achieve this goal as mentioned in the comments, there is something built into Java since version 6 which may be useful (but maybe a little overkill). I suggest this not because I believe it's particularly efficient but rather as an alternative to using a library.

Use JavaScript:

import javax.script.ScriptEngineManager;
import javax.script.ScriptEngine;

ScriptEngine jsRuntime = new ScriptEngineManager().getEngineByName("javascript");
String expression = "2+2"; //The expression you would to evaluate.
double result = (Double) jsRuntime.eval(expression);

edited Oct 12 '13 at 14:52

answered Oct 10 '13 at 17:18

sushain97

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this is a very clever solution – Dónal Oct 10 '13 at 20:32
1

Thank you, actually extremely helpful and will work for a wider variety of integrations. – metelofe Oct 10 '13 at 22:11

score 0 · Answer 2 · answered Oct 10 '13 at 17:09

0

Use the Integer.parseInt method to parse a String into an int, then add the values. Adding strings just concatenates them.

answered Oct 10 '13 at 17:09

rgettman

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I guess OP wants/needs to retrieve it as `4` instead of `2+2`. – Luiggi Mendoza Oct 10 '13 at 17:09

score 0 · Answer 3 · answered Oct 10 '13 at 17:09

0

You can use parseInt() method.

answered Oct 10 '13 at 17:09

DT7

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score 0 · Answer 4 · answered Oct 10 '13 at 20:29

It seems your question could be summarised as

How do I convert a String such as "2+2" to the number 4

Here's a solution that uses only the standard Java libraries:

    String sumExpression = "2+2";
    String[] numbers = sumExpression.split("\\+");

    int total = 0;

    for (String number: numbers) {
        total += Integer.parseInt(number.trim());
    }

    // check our result
    assert total == 4;

Adding numbers within a string in java

4 Answers4