Edit an object's methods after they've been created in Java

Edit an object's methods after they've been created in Java

In JavaScript one can create and edit an object's functions on the fly. Is
this possible with a Java object's methods? I am essentially wanting
something like this:
public class MyObject{
private int x;
public MyObject(){x = 0;}
public myMethod(){}
}
MyObject foo = new MyObject();
and later call something along the lines of:
foo.myMethod = new method({x = 42;});