Question

If I have code that looks like this:

Collection<Object> c = new HashSet<Object>();

will it still retain the properties that the collection will not be able to contain duplicate values. In other words, what would happen in the following situation?

String h = "Hello World!";
c.add(h);
c.add(h);

Answer 1

Yes, the behavior and properties of Set will still hold. c will only contain one instance of "Hello World!"

public static void main(String[] args)
{
    Collection<Object> c = new HashSet<Object>();
    String h = "Hello World!";
    c.add(h);
    c.add(h);
    System.out.println("c contains " + c.size() + " item(s): " + c);
    System.out.println("c is an instance of " + c.getClass());
}

The above main method outputs:

c contains 1 item(s): [Hello World!]
c is an instance of class java.util.HashSet