Adding new method to a class through reflection [duplicate]

Answer 1

No, not through reflection.

Reflection asks about classes and their members, you can change fields but you cannot create new ones. You cannot add new methods.

You can use a a bytecode manipulation library to add methods to classes; but why would you want to?

You can't call the methods anyway except via reflection as they would obviously not exist at compile time.

Maybe take a look at project Lombok - this is a annotation preprocessor that can add methods to classes at compile time. It will add getters and setters automagically as long as your classes are correctly annotated.

Answer 2

No. You can't add methods through reflection. In this case, I'll use a scripting language like Beanshell 2. Here's a DynamicObject class

public class DynamicObject
{

    bsh.Interpreter interpreter = null;

    public DynamicObject()
    {
        interpreter = new bsh.Interpreter();
    }

    public void addToSource(String... method)
    {
        try
        {
            String main = "";
            for (int i=0; i<lines.length; i++){
                main += lines[i] + "\n";
            }
            interpreter.eval(main);
        }
        catch (Exception e)
        {
            e.printStackTrace();
        }
    }

    public Object invoke(String methodname, Object... args)
    {
        try
        {
            return interpreter.getNameSpace().invokeMethod(methodname, args, bsh);
        }
        catch (Exception e)
        {
            e.printStackTrace();
        }
        return null;
    }

    public Object invoke(String methodname)
    {
        return invoke(methodname, (Object[])null);
    }

}

Now an example dynamic object will look like

DynamicObject testObj = new DynamicObject();

testObj.addToSource(

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

);

int added = testObj.invoke( "add", 5, 4 );   // is 9