Can byte-code manipulation change the return type of a Java method at run-time?

Question

I was wondering if it is possible to do something like this with byte-code manipulation:

public class Foo {
    public int getBlah() {
       return 1;
    }
}

public void hi(int x) {
    System.out.println("hi: " + x);
}

public void hi(String x) {
    System.out.println("wow: " + x);
}

Now I want to call:

hi(foo.getBlah());

and invoke the overloading hi method for the String parameter.

Answer 1

Can you handle a flagged value on hi(int x)? If yes you could do something like this:

public void hi(int x) {
    if (x == Integer.MIN_VALUE) {
        String newParam = getTheParamFromProxySomehow();
        hi(newParam);
        return;
    }    
    System.out.println("hi: " + x);
}

It is basically:

• Intercept through a proxy the getBlah() method
• Save (in a ThreadLocal?) whatever String parameter you want to pass to the overloaded hi method
• Return the flagged value such as 0, -1 or Integer.MIN_VALUE
• Do the trick above

It is a little hacky and it looks best when you don't have a primitive so you can use null as your flagged value. Hopefully someone has a better answer. :)