如何使用相同类型的对象创建对象

Question

I wonder if it is possible to get a new instance of an object, using other object of the same type.

public class Vegetable{
    private int ...
    //a lot of fields
    public Vegetable(Vegetable v) {
        //some magic here
    }
}

I am looking for an option, where i wouldn't copy each single field manually in the constructor, but rather use something like super(v) .

Answer 1

Java does not provide a default copy constructor.

However, Java does provide a method Object.clone() . You can call it on instances of classes that implement Cloneable. Otherwise, it will throw CloneNotSupportedException.

The default implementation creates a shallow copy . If your object contains references to other objects, only the references are copied. This is usually not what you want. To create a deeper, more independent copy, you can extend the default implementation.

You can create your own copy constructor, and this is sometimes useful. However, unlike clone() , a copy constructor will not necessary create another instance of the same class. A copy constructor for class T will always create a T, even if it's passed an instance of a subclass of T.