I am a Javascript developer and I starting to check out Java.
One question that I have is how I can perform forEach on a collection. I can't seem to find any such method in Java collections...
2 Answers
Since Java 5, you can use the enhanced for loop for this. Assume you have (say) a List<Thingy> in the variable thingies. The enhanced for loop looks like this:
for (Thingy t : thingies) {
// ...
}
As of Java 8, there's an actual forEach method on iterables that accepts a lambda function:
thingies.forEach((Thingy t) -> { /* ...your code here... */ });
If you have an existing method you want to use, you can use a method reference instead of an inline lambda:
thingies.forEach(this::someMethod); // Instance method on `this`
thingies.forEach(SomeClass::someMethod); // Static method on `SomeClass`
thingies.forEach(foo::someMethod); // Instance method on `foo` instance
3 Comments
Marko Topolnik
And if
your code here amounts to someMethod(t), you get to write just thingies.forEach(this::someMethod)
T.J. Crowder
@MarkoTopolnik: Oh very cool! I've added examples and a link to the JLS for that, thanks. (Haven't got into this Java 8 stuff much yet.)
Rand Random
The answer grows and grows in perfectness. :D
What you are trying to accomplish can only be done in a form similar to JavaScript, in Java 8 or newer. Java 8 added the forEach (defender) method on Iterable (for which Collection inherits)
9 Comments
Daniël Knippers
Strange answer, you are implying he cannot do a for each loop similar to JavaScript in Java < 8?
geoand
The user obviously does not want a for loop but a forEach method on a collection
T.J. Crowder
The enhanced
for loop (for (Thingy t : collectionOfT)) was added to Java 5 (e.g., many years ago), not Java 8.Marko Topolnik
@T.J.Crowder Since OP is explicitly asking for a
forEach method of the Collection interface, I think this answer fits best. The enhanced for loop also deserves a mention, but this answer fits the question squarely.Daniël Knippers
He is asking how to perform forEach on a collection, i.e. he is asking how to iterate a collection. Not necessarily a literal method by the name of
forEach. That would be my interpretation. |
methodfor this but only syntatic iteration in form of a for. Amethodwould be something like: collection.ForEach(//do something in here...);