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.

4 years ago

In Java 8, they introduced forEach. Using it List, Maps can be looped.

Loop a List using for each

List<String> someList = new ArrayList<String>();

someList.add("A");

someList.add("B");

someList.add("C");



someList.forEach(listItem -> System.out.println(listItem))

or

someList.forEach(listItem-> {

     System.out.println(listItem); 

});

Loop a Map using for each

Map<String, String> mapList = new HashMap<>();

    mapList.put("Key1", "Value1");

    mapList.put("Key2", "Value2");

    mapList.put("Key3", "Value3");



mapList.forEach((key,value)->System.out.println("Key: " + key + " Value : " + value));

or

mapList.forEach((key,value)->{

    System.out.println("Key : " + key + " Value : " + value);

});

4 years ago