How can I change Java method implementation of single instance?

Question

What is correct way to change method signature for single java object. Suppose I wanna change toString method.

myObject.metaClass.toString = { pritln "hello world" }

Looks like this code has problems. If I pass my object into other Java compiled object original toString will be called.

Other solution creates wrapper Object. It has different class from original one so it doesn't satisfy me

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Added:
1. I can't control creation process
2. I don't know how object was instantiated

So there is no groovy way to solve this problem? The only solution is to create Java wrapper class, wrap all methods and change one? This is a ...

Answer 1

If you would like to create an object that has a single method changed, there is a way to do that using "Anonymous Classes".

Whenever creating your object:

MyClass myObject = new MyClass() {
    public String toString() {
        ...implementation...
    }
}