How do I invoke a Java method when given the method name as a string?

Question

If I have two variables:

Object obj;
String methodName = \"getName\";

Without knowing the class of obj, how can I call the met

Answer 1

You should use reflection - init a class object, then a method in this class, and then invoke this method on an object with optional parameters. Remember to wrap the following snippet in try-catch block

Hope it helps!

Class<?> aClass = Class.forName(FULLY_QUALIFIED_CLASS_NAME);
Method method = aClass.getMethod(methodName, YOUR_PARAM_1.class, YOUR_PARAM_2.class);
method.invoke(OBJECT_TO_RUN_METHOD_ON, YOUR_PARAM_1, YOUR_PARAM_2);

Answer 2

for me a pretty simple and fool proof way would be to simply make a method caller method like so:

public static object methodCaller(String methodName)
{
    if(methodName.equals("getName"))
        return className.getName();
}

then when you need to call the method simply put something like this

//calling a toString method is unnessary here, but i use it to have my programs to both rigid and self-explanitory 
System.out.println(methodCaller(methodName).toString()); 

Answer 3

This sounds like something that is doable with the Java Reflection package.

http://java.sun.com/developer/technicalArticles/ALT/Reflection/index.html

Particularly under Invoking Methods by Name:

import java.lang.reflect.*;

public class method2 {
  public int add(int a, int b)
  {
     return a + b;
  }

  public static void main(String args[])
  {
     try {
       Class cls = Class.forName("method2");
       Class partypes[] = new Class[2];
        partypes[0] = Integer.TYPE;
        partypes[1] = Integer.TYPE;
        Method meth = cls.getMethod(
          "add", partypes);
        method2 methobj = new method2();
        Object arglist[] = new Object[2];
        arglist[0] = new Integer(37);
        arglist[1] = new Integer(47);
        Object retobj 
          = meth.invoke(methobj, arglist);
        Integer retval = (Integer)retobj;
        System.out.println(retval.intValue());
     }
     catch (Throwable e) {
        System.err.println(e);
     }
  }
}

Answer 4

I do this like this:

try {
    YourClass yourClass = new YourClass();
    Method method = YourClass.class.getMethod("yourMethodName", ParameterOfThisMethod.class);
    method.invoke(yourClass, parameter);
} catch (Exception e) {
    e.printStackTrace();
}

Answer 5

First, don't. Avoid this sort of code. It tends to be really bad code and insecure too (see section 6 of Secure Coding Guidelines for the Java Programming Language, version 2.0).

If you must do it, prefer java.beans to reflection. Beans wraps reflection allowing relatively safe and conventional access.

Answer 6

Here are the READY TO USE METHODS:

To invoke a method, without Arguments:

public static void callMethodByName(Object object, String methodName) throws IllegalAccessException, InvocationTargetException, NoSuchMethodException {
    object.getClass().getDeclaredMethod(methodName).invoke(object);
}

To invoke a method, with Arguments:

    public static void callMethodByName(Object object, String methodName, int i, String s) throws IllegalAccessException, InvocationTargetException, NoSuchMethodException {
        object.getClass().getDeclaredMethod(methodName, int.class, String.class).invoke(object, i, s);
    }

Use the above methods as below:

package practice;

import java.io.IOException;
import java.lang.reflect.InvocationTargetException;

public class MethodInvoke {

    public static void main(String[] args) throws ClassNotFoundException, NoSuchMethodException, SecurityException, IllegalAccessException, IllegalArgumentException, InvocationTargetException, IOException {
        String methodName1 = "methodA";
        String methodName2 = "methodB";
        MethodInvoke object = new MethodInvoke();
        callMethodByName(object, methodName1);
        callMethodByName(object, methodName2, 1, "Test");
    }

    public static void callMethodByName(Object object, String methodName) throws IllegalAccessException, InvocationTargetException, NoSuchMethodException {
        object.getClass().getDeclaredMethod(methodName).invoke(object);
    }

    public static void callMethodByName(Object object, String methodName, int i, String s) throws IllegalAccessException, InvocationTargetException, NoSuchMethodException {
        object.getClass().getDeclaredMethod(methodName, int.class, String.class).invoke(object, i, s);
    }

    void methodA() {
        System.out.println("Method A");
    }

    void methodB(int i, String s) {
        System.out.println("Method B: "+"\n\tParam1 - "+i+"\n\tParam 2 - "+s);
    }
}

Output:

Method A  
Method B:  
	Param1 - 1  
	Param 2 - Test