如何在Java中将对象添加到集合中？

Question

I am writing some JUnit tests for a bus stop but I am having trouble trying to create objects to be used through the tests:

public class StopTests {
  BusRoute rte = new BusRoute("250");
  Set<BusRoute> set = new Set<BusRoute>();
  BusStop stop = new BusStop(00000, "Staples Center", 90.0, 90.0, set);
...
}

My problem is that the test won't compile because Eclipse says "new Set()" cannot be instantiated. My intention is to add 'rte' into 'set' so that 'stop' can be created without compilation errors, but I am stumped on how to do this. I tried approaching it like:

public class StopTests {
  BusRoute rte = new BusRoute("250");
  Set<BusRoute> set = new Set<BusRoute>();
  set.add(BusRoute rte);
  BusStop stop = new BusStop(00000, "Staples Center", 90.0, 90.0, set);
...
}

but Eclipse gave me another error about not having an identifier following 'add'.

What would be the best way to approach this?

EDIT: This is what I have now:

public class StopTests {
  BusRoute rte = new BusRoute("250");
  Set<BusRoute> set = new HashSet<BusRoute>();
  set.add(rte);
  BusStop stop = new BusStop(00000, "Staples Center", 90.0, 90.0, set);
...
}

Answer 1

Set is an interface so cannot create an instance of it. You need to create and instance of Set implementations such as HashSet .

Try changing this:

Set<BusRoute> set = new Set<BusRoute>()

to

Set<BusRoute> set = new HashSet<BusRoute>()

Also to add the element in set you need to call add on set instance and not on BusRoute instance. So change this :

  rts.add(BusRoute rte);

to

  set.add(rte);

Answer 2

Your issue here is with this line: rts.add(BusRoute rte) . You don't need to prepend rte with its type: use rts.add(rte) instead.

Answer 3

Set is an interface, you need to instantiate with an implementation class:

Set<BusRoute> set = new HashSet<BusRoute>()

Please see these links

Set examples

Set API

Cheers !!

Answer 4

Set is abstract so it cannot be instantiated. You need to use an implementation of Set , such as HashSet .

public class StopTests {

    public void someMethod() {
        BusRoute rte = new BusRoute("250");
        Set<BusRoute> set = new HashSet<BusRoute>();
        set.add(rte);
        BusStop stop = new BusStop(00000, "Staples Center", 90.0, 90.0, set);
        ...
    }
}