How to access an instance of a class?

Question

Java

I'm learning java myself, tell me how to refer to another class other than declaring it again?

public class Main {
    public static void main(String[] args) {
        Cat cat = new Cat();
        Dog dog = new Dog();
        cat.setAge(8);
        System.out.println( cat.getAge() );
    }
}

public class Dog {
    private int age;
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
}

public class Cat {
    private int age;
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
    public void question() {
        // как тут обратится к Dog?
        Dog dog = new Dog();  // так?
    }
}

Answer 1

You are working with an instance of a class, that is, an object.
If you want to work with the data of the Dog class in Cat, then create an object, that is, as you wrote

Answer 2

1) pass this class as an argument
2) If you need to instantiate a class and do something with it, then yes:

public void question() {
        Dog dog = new Dog();
    }

but if you need to refer to a specific previously created class instance, then:

public void question(Dog dog) {
        int age = dog.getAge();
    }

Answer 3

public class Main {

    public static void main(String[] args) {
        Cat cat = new Cat();
        cat.setName("Vasyka");

        Dog dog = new Dog();
        dog.setName("Barbos");

        Human human = new Human();
        human.setCat(cat);
        human.setDog(dog);

        System.out.println(human.getDog().voice());
        System.out.println(human.getCat().voice());
    }
}

interface Animal {
    String voice();
}

abstract class Pet implements Animal {
    private String name;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

class Dog extends Pet {
    @Override
    public String voice() {
        return getName() + " says Woof";
    }
}

class Cat extends Pet {
    @Override
    public String voice() {
        return getName() + " says Meaw";
    }
}

class Human {
    private Pet cat;
    private Pet dog;

    public Pet getCat() {
        return cat;
    }

    public void setCat(Pet cat) {
        this.cat = cat;
    }

    public Pet getDog() {
        return dog;
    }

    public void setDog(Pet dog) {
        this.dog = dog;
    }
}

Answer 4

public void question(Dog dog){
//Тут соответственно, то что ты хочешь от пса
}

Of course, the interaction of a cat and a dog will take place in the 3rd grade

Cat brit = new Cat();
Dog mops = new Dog();

brit.question(mops)  //кот обратился к собаке через метод question

It is best to put the question in interface.