Question

In Java is there anyway to have one constructor that will accept an array or a collection? I have been fiddling with this for a while but I don’t think it is possible.

I would like to be able to initialize MyClass, like this:

MyClass c = new MyClass({"rat", "Dog", "Cat"});

And like this:

LinkedList <String> l = new <String> LinkedList();
l.add("dog");
l.add("cat");
l.add("rat");
MyClass c = new MyClass(l);

This is what MyClass looks like. What can I make XXX be so that this will work? I know that I could overload the constructor, but if I can minimize code that would be awesome right?

public class MyClass{

   private LinkedHashSet <String> myList;

   public MyClass(XXX <String> input){
       myList = new LinkedHashSet <String> ();
       for(String s : input){
           myList.put(s);
       }

   }

}

Answer 1

You can declare two constructors and call second from first:

class MyClass {
    public MyClass(String... x) {
        // for arrays
        // this constructor delegate call to the second one
        this(Arrays.asList(x));
    }
    public MyClass(List<String> x) {
        // for lists
        // all logic here
    }
}

Calls would look like

new MyClass(new ArrayList<String>());
new MyClass("dog", "cat", "rat");
new MyClass(new String[] {"rat", "Dog", "Cat"});

Since there’s only one line of code in the first constructor, it’s pretty minimalistic.