Arraylist of classes

Question

In my hw assignment my professor says to create a data field of type ArrayList. He wants them to be instances of a class. I'm not exactly sure what that means, but my guess is

 ArrayList<CLassName> list = ArrayList<ClassName>();

Can anyone confirm this for me?

• Pshemo: I doubt that anyone beside your professor could confirm it, but your guess seems very probable. Anyway you can also improve you code by using List interface as reference to ArrayList.
• user456814: You should confirm this with your professor, because only he/she knows what he/she really means and expects.
• Chris: @Pshemo List<CLassName> list = ArrayList<ClassName>();? What would the difference be between the two?
• tbodt: Who is toggling their downvote? Why?
• Pshemo: @tbodt It was me, was testing vote animations :)

Answer 1

You can use something like this:

List<String> list = new ArrayList<String>();

Since Java SE 1.7, it can a little simpler:

List<String> list = new ArrayList<>();

Answer 2

Yes.

NOTE: The rest is background knowledge about ArrayLists.

Let's say you want an ArrayList of Strings. Keep in mind Strings are Objects.

// Creates ArrayList
ArrayList<String> list = ArrayList<String>();
// Adds elements to ArrayList
list.add("Hello");
list.add("world!");
// Iterate through ArrayList
for (String str : list) {
 // Print the String in the list.
 System.out.print(str + " ");
}
// Print newline character.
System.out.print("\n");

The for (String str : list) is a for each loop which allows you to iterate through each element in the list.

• tbodt: That doesn't answer the question.
• tbodt: Now it does, but it has a lot of redundant content.
• Anubian Noob: @tbodt I need to get into the habit of reading the questions before answering, but what about now.
• tbodt: I think that the OP is learning about how to use ArrayLists in his class.
• Chris: "Let's say you want an ArrayList of Strings. Keep in mind Strings are Objects." That is literally all I needed to see to confirm what I was looking for. I always forget that Strings are objects because my first programming class they taught us that they were primitives. And that was my belief for about a year, so somtimes it just slips my mind.

Answer 3

Yes, that's right. I do, however, recommend this instead:

List<ClassName> list = new ArrayList<ClassName>();

That way you can change the type of list in just one place instead of two.