Java – How to use the java for each loop with custom classes

classforeachjava

I think most coders have used code like the following :


ArrayList<String> myStringList = getStringList();
for(String str : myStringList)
{
   doSomethingWith(str);
}

How can I take advantage of the for each loop with my own classes? Is there an interface I should be implementing?

Best Solution

You can implement Iterable.

Here's an example. It's not the best, as the object is its own iterator. However it should give you an idea as to what's going on.

Related Solutions

Java – How to efficiently iterate over each entry in a Java Map

Map<String, String> map = ...
for (Map.Entry<String, String> entry : map.entrySet()) {
    System.out.println(entry.getKey() + "/" + entry.getValue());
}

On Java 10+:

for (var entry : map.entrySet()) {
    System.out.println(entry.getKey() + "/" + entry.getValue());
}

Java – How does the Java ‘for each’ loop work

for (Iterator<String> i = someIterable.iterator(); i.hasNext();) {
    String item = i.next();
    System.out.println(item);
}

Note that if you need to use i.remove(); in your loop, or access the actual iterator in some way, you cannot use the for ( : ) idiom, since the actual iterator is merely inferred.

As was noted by Denis Bueno, this code works for any object that implements the Iterable interface.

Also, if the right-hand side of the for (:) idiom is an array rather than an Iterable object, the internal code uses an int index counter and checks against array.length instead. See the Java Language Specification.

Best Solution

Related Solutions

Java – How to efficiently iterate over each entry in a Java Map

Java – How does the Java ‘for each’ loop work

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