Creating a new ArrayList in Java

Question

Assuming that I have a class named Class,

And I would like to make a new ArrayList that it's values will be of type Class.

My question is that: How do I do that?

I can't understand from Java Api.

I tried this:

ArrayList<Class> myArray= new ArrayList ArrayList<Class>;

Solution 1

You are looking for Java generics

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

Here's a tutorial http://docs.oracle.com/javase/tutorial/java/generics/index.html

Solution 2

If you just want a list:

ArrayList<Class> myList = new ArrayList<Class>();

If you want an arraylist of a certain length (in this case size 10):

List<Class> myList = new ArrayList<Class>(10);

If you want to program against the interfaces (better for abstractions reasons):

List<Class> myList = new ArrayList<Class>();

Programming against interfaces is considered better because it's more abstract. You can change your Arraylist with a different list implementation (like a LinkedList) and the rest of your application doesn't need any changes.

Solution 3

You're very close. Use same type on both sides, and include ().

ArrayList<Class> myArray = new ArrayList<Class>();

Solution 4

You can use in Java 8

List<Class> myArray= new ArrayList<>();

Solution 5

Fixed the code for you:

ArrayList<Class> myArray= new ArrayList<Class>();

View more solutions

Comments

[AlexR]

Never use this! It is extremely bad practice to use concrete class at the left side of assignment when interface is available.

[Mr. Lance E Sloan]

That link to a tutorial PDF from Sun is broken. This series of web pages from Oracle should be helpful: docs.oracle.com/javase/tutorial/java/generics/index.html

[Noumenon]

Not sure what's wrong, this looks like all the other answers. They must have edited?

[Kyle Clegg]

I often see just "List" on the left side (like in the accepted answer). Why do you suggest ArrayList on both sides?

[Zakaria]

@KyleClegg mellamokb just took the code line from the question. If your question was about "List vs ArrayList", you can find some answers here : stackoverflow.com/questions/2279030/…

[Zakaria]

@AlexR Nothing can prevent you from using the ArrayList class on the left type if you want to use ArrayList's specific methods (trimToSize, removeRange, ...) as the List interface doesn't contain these methods.

[Erik Humphrey]

Can also be shortened to List<MyClass> list = new ArrayList<>();, at least in Java 8.

[Pontios]

What is the advantage of not writing Class in the <> of the right handside ?