Java ArrayList强制转换问题

Question

I have an ArrayList in Java which is full of int's. I am accessing it through get method. Now, I need array list int objects as ints to perform some operations. So, what I am doing is,

int i = Integer.parseInt(arraylist.get(position).toString()) + 100 ...

Is there any-other nice way to do it (means efficiently) ?

Answer 1

Yes - don't convert to a string and back!

int i = arrayList.get(position).intValue() + 100;

Or using auto-unboxing:

int i = arrayList.get(position) + 100;

As noted in comments, I'm happy with auto-unboxing when the expression is just used in assignment expression (or as a method argument) - when it's used as part of an arithmetic expression, I generally prefer to make it explicit.

(Note that your list will be full of Integer references, not int values.)

Answer 2

What version of Java are you using? Since Java 1.5 the 'autoboxing' feature should take care of this for you.

int i = arrayList.get(position) + 100;

Answer 3

Perhaps:

List<Integer> myList = new ArrayList<Integer>();
myList.put(1);
myList.put(2);
...
int num = myList.get(index) + 100;

Or do whatever you like, collection will contain only Integers so you don't have to convert it. Plus, autoboxing takes care for int->Integer and back.