Check if ArrayList<String> contains part of a string in Java

Question

Say I have an ArrayList:

<string1.4>
<string2.4>
<string3.4>

and I wish to return the first element of the ArrayList that contains "string1" as part of that element's string.
E.g.

arrayList.containsSubString('string1'); 

How could this be done other than iterating through each of the elements of the ArrayList and checking if "string1" is a substring of that element's string?

• Asaf: what are you allowed to change? do you get a reference to the ArrayList and return the first match or do you have control over the inserting of the data in the list?

Answer 1

The only way I can think of is doing something like:

strs.get(strs.indexOf(new Object() {
 @Override
 public boolean equals(Object obj) {
 return obj.toString().contains(s);
 }
}));

Don't know if it is considered good practice though.

• TookTheRook: Works for my purposes. Thanks! arrayList.toString()!
• shareef: great i can use startswith as well

Answer 2

With an ArrayList there is no other option than iterating through it. But you could use other data structures like a prefix tree (e.g. a ternary search tree, see this java sample).

• Vishal_Kotecha: java sample link is broken

Answer 3

I think iterating though the list and checking each item is the fastest way. And it is also the way every one understand your code. (except of building your own data structure).

---

Anyway you can also use org.apache.commons.collections.CollectionUtils#find(Collection, Predicate)

find(java.util.Collection collection, Predicate predicate) Finds the first element in the given collection which matches the given predicate.

• Peter Lawrey: These methods use loops for you.
• Ralph: @Peter Lawrey: yes - it is only an way to reuse the compare logic (Predicate) -- Because I understand the question to search for other ways than the traditional for-each-if-check-return way.

Answer 4

Can't. Even if there was an equivalent of List.contains() it just does a linear search under the hood.

Answer 5

You can use a NavigableSet

NavigableSet<String> set = new TreeSet<String>();
// add strings
String find =
String firstMatch = set.ceiling(find);