Does Java have a built-function to allow me to linearly search for an element in an array or do I have to just use a for loop?
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5 Answers
There is a contains method for lists, so you should be able to do:
Arrays.asList(yourArray).contains(yourObject);
Warning: this might not do what you (or I) expect, see Tom's comment below.
4 Comments
Casebash
Thats pretty short, but this use case is common enough that they really should have added a function into the language
Tom Hawtin - tackline
Be careful not to use that with primitive arrays.
Tom Hawtin - tackline
@Casebash It compiles but doesn't do what you expect. Because of evil varargs, the argument gets treated as an array of arrays of primitives.
user2743055
With Java 8, you can do this:
int[] haystack = {1, 2, 3};
int needle = 3;
boolean found = Arrays.stream(haystack).anyMatch(x -> x == needle);
You'd need to do
boolean found = Arrays.stream(haystack).anyMatch(x -> needle.equals(x));
if you're working with objects.
1 Comment
Trenton
True, but if you're working with an
ArrayList, doing boolean found = haystack.contains(needle) is much easier to read.Use a for loop. There's nothing built into array. Or switch to a java.util Collection class.
Comments
You might want to consider using a Collection implementation instead of a flat array.
The Collection interface defines a contains(Object o) method, which returns true/false.
ArrayList implementation defines an indexOf(Object o), which gives an index, but that method is not on all collection implementations.
Both these methods require proper implementations of the equals() method, and you probably want a properly implemented hashCode() method just in case you are using a hash based Collection (e.g. HashSet).
Comments
You can use one of the many Arrays.binarySearch() methods. Keep in mind that the array must be sorted first.
3 Comments
Nikita Rybak
That's an option only is elements of array are comparable themselves.
krock
We can only assume that this is the case, e.g. an array of ints, Strings, etc. You could always provide a custom
Comparator to sort and search if needed.
rogerdpack
hard to believe there's no Arrays.search ... <sigh>