数学计算表达式的字符串（“3+2+4+5”）得出结果返回Integer

package demo1;

import javax.script.ScriptEngine;
import javax.script.ScriptEngineManager;
import java.util.Scanner;

public class demo1 {
    public static void main(String args[]) throws Exception{
        String string = "3+3+2+1";
        ScriptEngineManager manager = new ScriptEngineManager();
        ScriptEngine scriptEngine = manager.getEngineByName("JavaScript");
        System.out.println((Integer)scriptEngine.eval(string));
        }
    }