如何从Java中的其他类创建对象

Question

I am pretty new to java, and was wondering how to create an object of a different class. I would extend that class, however I am already extending another. For example:

public class Dog extends Animal{
    //How do I create a "Chupacabra" object in here?
    Chupacabra jeff = new Chupacabra();
    //I've been doing this^, but it says "Cannot be resolved as type"
}

public class Chupacabra {

}

Or am I crazy? I know it doesn't make much sense to make a Chupacabra object in there, but... I need to.

Answer 1

public class Dog extends Animal{        
    Chupacabra ch = new Chupacabra(); //creating "Chupacabra" object
}

class Chupacabra {

}

You can't have two public classes under one .java name; so I removed 'public' from the second class.

If you want, you can keep the second class as "Chupacabra.java"

Answer 2

If I understand your question, and assuming Chupacabra is in the same package as Dog . You could use the default constructor like -

public class Dog extends Animal{
  //How do I create a "Chupacabra" object in here?
  private Chupacabra myChupacabra = new Chupacabra();
}

If Chupacabra is in a different package from Dog then you will need to import Chupacabra .

Answer 3

If you want to merely have an instance of Chupacabra class inside of the Dog class, then you can declare it as an instance variable, as such:

Dog.java :

public class Dog extends Animal{
    Chupacabra myChupacabra = new Chupacabra();

    //...
}

Chupacabra.java :

public class Chupacabra {

}

Note that the Dog class needs to be declared in Dog.java and that the Chupacabra class needs to be declared in Chupacabra.java .

For more information on declaring member variables in Java, please see the documentation .