Most efficient way to see if an ArrayList contains an object in Java

Question

I have an ArrayList of objects in Java. The objects have four fields, two of which I\'d use to consider the object equal to another. I\'m looking for the most efficient wa

Answer 1

Given your constraints, you're stuck with brute force search (or creating an index if the search will be repeated). Can you elaborate any on how the ArrayList is generated--perhaps there is some wiggle room there.

If all you're looking for is prettier code, consider using the Apache Commons Collections classes, in particular CollectionUtils.find(), for ready-made syntactic sugar:

ArrayList haystack = // ...
final Object needleField1 = // ...
final Object needleField2 = // ...

Object found = CollectionUtils.find(haystack, new Predicate() {
   public boolean evaluate(Object input) {
      return needleField1.equals(input.field1) && 
             needleField2.equals(input.field2);
   }
});