Use interface or type for variable definition in java?

Question

ArrayList aList = new ArrayList();

List aList = new ArrayList();

What\'s the difference between these two and which is better to use and why?

Answer 1

Both are deprecated since Java 1.5.

It should be:

List list = new ArrayList();
// or whatever data type you are using in your list

Please read Effective Java by Joshua Bloch, especially these two items:

• 23: Don't use raw types in new code (this is even available online)
• 52: Refer to objects by their interfaces

BTW, if you use Guava, you have a factory method for constructing an ArrayList so you don't have to repeat the type parameter:

List list = Lists.newArraylist();