Evaluate Mathematical Expressions in String using Java

To evaluate mathematical expression in String, use Nashorn JavaScript in Java i.e. scripting. Nashorn invoke dynamics feature, introduced in Java 7 to improve performance.

For scripting, use the ScriptEngineManager class for the engine −

ScriptEngineManager scriptEngineManager = new ScriptEngineManager();
ScriptEngine scriptEngine = scriptEngineManager.getEngineByName("JavaScript");

Now for JavaScript code from string, use eval i.e. execute the script. Here, we are evaluating mathematical expressions in a string −

Object ob = scriptEngine.eval("9 + 15 + 30");
System.out.println("Result of evaluating mathematical expressions in String = "+ob);

Example

 Live Demo

import javax.script.ScriptEngine;
import javax.script.ScriptEngineManager;
public class Main {
   public static void main(String[] args) throws Exception {
      ScriptEngineManager scriptEngineManager = new ScriptEngineManager();
      ScriptEngine scriptEngine = scriptEngineManager.getEngineByName("JavaScript");
      // JavaScript code from String
      Object ob = scriptEngine.eval("9 + 15 + 30");
      System.out.println("Result of evaluating mathematical expressions in String = "+ob);
   }
}

Output

Result of evaluating mathematical expressions in String = 54