I have a collection and I would like to know if at least one element meets some condition. Essentially, what some does in JavaScript, I would like to do on a collection!
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4 Answers
As of Java 8, you can convert the Collection into a Stream and use anyMatch as in the following example.
import java.util.Arrays;
import java.util.List;
public class SomeExample {
public static void main(String[] args) {
List<Integer> list = Arrays.asList(1, 2, 3, 4, 5, -6, 7);
boolean hasNegative = list.stream().anyMatch(x -> x < 0);
if (hasNegative) {
System.out.println("List contains some negative number");
}
else {
System.out.println("List does not contain any negative number");
}
}
}
Comments
Check out Guava's Iterables class and its any() implementation.
More or less the same thing as the Commons Collections example in the other answer, but genericized:
List<String> strings = Arrays.asList("ohai", "wat", "fuuuu", "kthxbai");
boolean well = Iterables.any(strings, new Predicate<String>() {
@Override public boolean apply(@Nullable String s) {
return s.equalsIgnoreCase("fuuuu");
}
});
System.out.printf("Do any match? %s%n", well ? "Yep" : "Nope");
2 Comments
Has QUIT--Anony-Mousse
+1 The lack of generics is a major drawback of commons collections.
Dave Newton
@Anony-Mousse Yeah; it's a pain, although I still use it too :/
You can use CollectionUtils from Apache commons-collections:
List<Integer> primes = Arrays.asList(3, 5, 7, 11, 13)
CollectionUtils.exists(primes, even); //false
Where even is a predicate:
Predicate even = new Predicate() {
public boolean evaluate(Object object) {
return ((Integer)object) % 2 == 0;
}
}
Or in an inlined version:
List<Integer> primes = Arrays.asList(2, 3, 5, 7, 11, 13)
CollectionUtils.exists(primes, new Predicate() {
public boolean evaluate(Object object) {
return ((Integer)object) % 2 == 0;
}
});
Yes, it is ugly for two reasons:
- Java does not (yet) support functions as first-class citizens, which are emulated with Single-Abstract-Method interface.
commons-collectionsdoes not support generics.
On the other hand in modern JVM languages like Scala you can write:
List(3,5,7,11,13,17).exists(_ % 2 == 0)
answered Jan 24, 2012 at 17:21
Tomasz Nurkiewicz
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4 Comments
axtavt
Another third-party library to support this method is Google Guava, it has
Iterables.any().
Louis Wasserman
And Guava supports generics. ;)
David Conrad
Java 8 will have lambdas. Also, SAM classes are now called functional interfaces.
Java doesn't have this feature built-in. Javascript's some() accepts a function pointer as an argument, which is not something that's natively supported in Java. But it should be fairly straight forward to emulate the functionality of some() in Java using a loop and and an interface for the callback functionality.
1 Comment
xlem
It accepts a function, but this is not the same thing as a function pointer.