@Delegate vs. Extends

// "favor composition over inheritance" ~Effective Java

class Parent {
    def getAll() {
        String resp = ""
        2.times {
            resp += get(it)
        }
        return resp
    }
    
    def get(def i) {
        "get PARENT $i\n"
    }
}

class Child1 extends Parent {
    def get(def i) {
        "get CHILD $i\n" // is used by parent's getAll
    }
}

class Child2 {
    @Delegate Parent p = new Parent() // decorated Parent instance
    
    def get(def i) {
        "get CHILD $i\n" // not used by parent's getAll
    }
}

Parent c1 = new Child1()
assert c1.getAll() == "get CHILD 0\nget CHILD 1\n" // calls child's get()
assert c1.get(0) == "get CHILD 0\n"

//Parent c2 = new Child2() // Child2 is not a Parent!
Child2 c2 = new Child2()
assert c2.getAll() == "get PARENT 0\nget PARENT 1\n" // calls parent's get()
assert c2.get(0) == "get CHILD 0\n"