class Dog {
    private String name;
    public Dog(String name) {
        this.name = name;
    }
}

class DogHolder {
    public Dog dog;
    public DogHolder(Dog dog) {
        this.dog = dog;
    }
}

public class Sample {
    void sample() {
        DogHolder d1 = new DogHolder(new Dog("Fido"));
        DogHolder d2 = new DogHolder(new Dog("Rex"));
        swap(d1, d2);
    }
    void swap(DogHolder d1, DogHolder d2) {
        Dog temp = d1.dog;
        d1.dog = d2.dog;
        d2.dog = temp;
    }
}