Java lists strange size malfunction

Question

I initialize a list, like this:

public List<Edge> edges = new ArrayList<Edge>(8);

After that, I would like to get its size, but following code gives zero.

System.out.println("SIZE: " + edges.size());

There isn't any value change or method call beetwen two lines. What can causes this?

The constructor you use instantiate an array with the given capacity. `size()` gives the number of elements in the list, not the underlying array length. Those things are unrelated. — Alexis C., Apr 25 '15 at 15:57
http://docs.oracle.com/javase/7/docs/api/java/util/ArrayList.html#size() — Zhenxiao Hao, Apr 25 '15 at 15:59

score 1 · Answer 1 · answered Apr 25 '15 at 15:59

1

The parameter to your constructor is the capacity.

The capacity is the number of elements that the underlying array can hold before it needs resizing.

answered Apr 25 '15 at 15:59

folkol

score 0 · Answer 2 · answered Apr 25 '15 at 15:58

0

The size of a List is the amount of elements in it, not the size you initialized it with.

answered Apr 25 '15 at 15:58

Distjubo

Yes, but when I try to add an element I get an exception. – Apr 25 '15 at 15:58
What kind of exception? without a stacktrace I can't help you. – Distjubo Apr 25 '15 at 16:02
`java.lang.IndexOutOfBoundsException: Invalid index 0, size is 0` – Apr 25 '15 at 16:06
what about a stacktrace? – Distjubo Apr 25 '15 at 16:09
Use the "add" method without an index, since you have no positions to insert into yet (with size 0). That is: "add(obj)" instead of "add(0, obj)". – folkol Apr 25 '15 at 16:23
There are values in it, I have tested. This exception comes, when I try to replace them. – Apr 25 '15 at 19:20

2 Answers2