An interview question about Java reflection

Question

public class Test {
    // 修改方法createObject内容,实现main里面的两处打印 
    public static void main(String[] arges) throws Exception {  
        IA ia = (IA) createObject(IA.class.getName() + "$getName =Abc");
        System.out.println(ia.getName()); //output: Abc
        ia = (IA) createObject(IA.class.getName() + "$getName= Bcd");
        System.out.println(ia.getName()); //output: Bcd
    }

    // please coding in createObject for true output
    public static Object createObject(String str) throws Exception {
        // your coding
    }

    interface IA {
        String getName();
    }

}

Through Google, I learned about coding through the use of reflection and dynamic proxies. But when I tried coding, I found that I couldn't do it...

Answer 1

What about this?

public class Test {
    public static void main(String[] arges) throws Exception {
        IA ia = (IA) createObject(IA.class.getName() + "$getName =Abc");
        System.out.println(ia.getName()); //output: Abc
        ia = (IA) createObject(IA.class.getName() + "$getName= Bcd");
        System.out.println(ia.getName()); //output: Bcd
    }

    // please coding in createObject for true output
    public static Object createObject(String str) throws Exception {
        String[] split = str.split("\\$getName\\s?=\\s?");
        String classname = split[0];
        String value = split[1];
        return Proxy.newProxyInstance(Class.forName(classname).getClassLoader(), new Class[] { IA.class },
                (proxy, method, args) -> {
                    if ("getName".equals(method.getName()))
                        return value;
                    throw new Exception();
                });
    }

    interface IA {
        String getName();
    }
}

Outputs:

Abc
Bcd

Answer 2

I would do it like this:

public static Object createObject(String str) throws Exception {
      String value = str.split("=")[1].trim();
      return (IA) () -> value;
    }

There is not really reflection needed because we only care about the part after the equation mark.

Answer 3

As the class name and method name are provided in the parameter, I made no assumption on the IA interface. Everything is dynamic.

// please coding in createObject for true output
public static Object createObject(String str) throws Exception {
    final String className = str.substring(0, str.lastIndexOf("$"));
    final String methodName=str.substring(str.lastIndexOf("$")+1,str.indexOf("=")).trim();
    final String value = str.substring(str.indexOf("=") + 1).trim();
    return Proxy.newProxyInstance(Class.forName(className).getClassLoader(), new Class[] { Class.forName(className) },
            (proxy, method, methodArgs) -> {
                if (method.getName().equals(methodName)) {
                    return value;
                } else {
                    throw new UnsupportedOperationException("Unsupported method: " + method.getName());
                }
            });
}