String with math operators to Integer [duplicate]

Question

I have a string with math operators which I need to turn into an int (the answer).

The below code does not work, but I'm not sure how I can get the answer variable to work.

String question;
int answer;

question = "7/7+9-9*5/5";
answer = Integer.parseInt(question);

Answer 1

1. Javascript Engine

public class MainTest {
    public static void main(String[] args)throws Exception {
        ScriptEngineManager manager = new ScriptEngineManager();
        ScriptEngine engine = manager.getEngineByName("js");
        Object result = engine.eval("7/7+9-9*5/5");
        System.out.println(result);
    }
}

2. Java Compiler

a) Compile string into Java class

b) Load the class using a custom ClassLoader.

c) Excute it using reflect.

Here's a sample:

import java.io.IOException;
import java.lang.reflect.Method;
import java.net.URI;
import java.util.Arrays;

import javax.tools.JavaCompiler;
import javax.tools.JavaFileObject;
import javax.tools.SimpleJavaFileObject;
import javax.tools.ToolProvider;


public class MainTest{
    public static void eval(String str) throws Exception{
        StringBuffer sb = new StringBuffer();
        sb.append("public class TempClass{\n");
        sb.append("    public void run(){\n");
        sb.append("        " + str + "\n");
        sb.append("    }\n");
        sb.append("}\n");
        System.out.println(sb.toString());
        Class clazz = new EvalClassLoader().findClass(sb.toString());

        Method method = clazz.getMethod("run");
        method.invoke(clazz.newInstance());
    }

    public static void main(String[] args) throws Exception {
        eval("System.out.println(7/7+9-9*5/5);");
    }
}

/**
 * A custom class Loader.
 */
class EvalClassLoader extends ClassLoader{
    private String tempCLassName = "TempClass";
    @Override
    protected Class<?> findClass(String codeStr) throws ClassNotFoundException {
        JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
        JavaFileObject file = new ClassFromString(tempCLassName, codeStr.toString());

        // Start a compile task
        Iterable<JavaFileObject> compilationUnits = Arrays.asList(file);
        JavaCompiler.CompilationTask task = compiler
                    .getTask(null, null, null, null, null, compilationUnits);
        if(task.call()){
            return loadClass(tempCLassName);
        }
        return null;
    }

}

/**
 * A Java class constructed from String.
 */
class ClassFromString extends SimpleJavaFileObject{
    private String code;

    public ClassFromString(String className,String code){
        super(URI.create("string:///" + className.replace('.', '/') +
                Kind.SOURCE.extension), Kind.SOURCE);
        this.code = code;
    }

    @Override
    public CharSequence getCharContent(boolean ignoreEncodingErrors)
            throws IOException {
        return code;
    }

}