What if I annotate User owner with DEPTH_ONE? Generate owner = new User(cart.owner) ? Doesn't. Items = ForeignCollectionImpl.create(cart.getItems()) and now for the magic trick - is the given method a copy constructor or an empty constructor? or if we assume a setter/addAll exists for the collection's contents if we assume a copy constructor exists for the collection:ĭiscounts = new CollectionImpl(cart.getCollectionImpl()) The disadvantage is that any user of the class may keep a copy and modify it at any time later, which leads to hard to find bugs. (*) Using final with mutable collections which are exposed to the outside makes sometimes sense as it allows to modify them without providing any methods for it. This allows to simulate the copy constructor easily and to reuse existing objects. It turned more complicated than I thought, mostly because of my example not matching what I was thinking about.ītw., some strange languages have assign, which copies the content of one instance into another. the user would most probably implement `apply` using `HashMultiset::create` tItems(HashMultiset.create(cart.getItem()) if lombok knew `HashMultiset` or if we could feed it with HashMultiset::create, then it'd use your line with a final field, the as specified won't work, but lets ignore it was initially empty, otherwise we'd need also discounts.clear() However, it's possible to make it configurable: It's still a bit complicated without Lombok being omniscient w.r.t. I agree, that the full-depth copy constructor is outside of the Lombok scope, but I'd like to get a depth-one copy constructor one day. When you need a copy of the cart, you only want to shallowly copy the Multiset, as the user and the items themselves are separate entities, which should stay as they're when you play with the cart. Usually, you don't want to copy all members.Ī typical example would be a shopping cart having a User containing a Multiset. The members of these collections may be immutables or other objects, which are not "owned" and needn't be copied. I guess, what's usually needed is a sort of depth-one copy: My object contains some mutable parts like collections (or some obsolete crap like Date), which it "owns". You obviously mean the creation of a completely new object graph, which (except for immutable members) has nothing in common with the original. If a constructor does not accept any parameters, it is known as a no-argument constructor.Deep copying is very and rather underspecified. 
Similar to methods, a Java constructor may or may not have any parameters (arguments). In Java, constructors can be divided into 3 types: Hence, the program prints the value of the name variables as Programiz. And, the value of the name variable is initialized.
Here, when the object is created, the Main() constructor is called. Notice the statement of creating an object of the Main class. Inside the constructor, we are initializing the value of the name variable. In the above example, we have created a constructor named Main(). Recommended Reading: Why do constructors not return values It has the same name as that of the class and doesn't have a return type. Unlike Java methods, a constructor has the same name as that of the class and does not have any return type. A constructor in Java is similar to a method that is invoked when an object of the class is created.
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