The history of element iteration
last modified July 16, 2024
In this article we look at the history of element iteration in Java.
On of the most common tasks in programming is to iterate over a collection of data. This tutorial shows how element iteration evolved with Java language over the course of time.
Enumeration
In the early days of Java, Enumeration was used to iterate over
elements of data. The Enumeration interface defines the methods by
which we can enumerate (obtain one element at a time) the elements in a
collection of objects. The two primary collection classes were
Vector and Hashtable.
Today, Enumeration, Vector, and Hashtable
are considered obsolete. They are not deprecated, however.
import java.util.Enumeration;
import java.util.Vector;
void main() {
Vector items = new Vector();
items.add("coin");
items.add("pen");
items.add("chair");
items.add("lamp");
items.add("cup");
items.add("spoon");
Enumeration itemsEn = items.elements();
while (itemsEn.hasMoreElements()) {
System.out.println(itemsEn.nextElement());
}
}
We have a vector of strings. We use the Enumeration to
loop over the elements of the vector.
Enumeration itemsEn = items.elements();
The elements method returns the the Enumeration
of the vector.
while (itemsEn.hasMoreElements()) {
System.out.println(itemsEn.nextElement());
}
The elements are traversed in a while loop. The hasMoreElements
returns true while there are still more elements to extract,
and false when all the elements have been enumerated.
Iterator
Java 1.2 introduced the standard collection classes (List,
Set, Map), and the Iterator.
Iterator brings the Iterator design pattern, which is a
common behavioral pattern used to access the elements of a collection object in
sequential manner without any need to know its underlying representation.
import java.util.Iterator;
import java.util.List;
void main() {
List<String> items = List.of("coin", "ball", "lamp", "spoon");
Iterator it = items.iterator();
while (it.hasNext()) {
System.out.println(it.next());
}
}
In the example, we loop over a list of elements with Iterator.
List<String> items = Arrays.asList("coin", "ball", "lamp", "spoon");
We use the Arrays.asList method to define a list in one line.
Iterator it = items.iterator();
We get the iterator from the list using the iterator method.
while (it.hasNext()) {
System.out.println(it.next());
}
We go through the list of elements in a while loop. We use the hasNext
and next methods of iterator.
Iterable and enhanced for loop
Java 5 introduced generics, Iterable, and the enhanced for loop.
The Iterable interface allows an object to be the target of the
enhanced for loop statement. An Iterable is an object that contains
a series of elements that can be iterated over. It has one method that produces
an Iterator.
import java.util.List;
void main() {
List<String> items = List.of("coin", "ball", "lamp", "spoon");
for (String item: items) {
System.out.println(item);
}
}
The example uses an enhanced for loop to traverse list elements. The creation of
the iterator and calls to the hasNext and next methods
are not explicit, but they still take place behind the scenes.
Java forEach method
Java 8 introduced the forEach method. The forEach
method performs the given action for each element of the Iterable
until all elements have been processed or the action throws an exception.
The
forEach method uses an internal iterator, while previous
methods used an external iterator.
import java.util.List;
void main() {
List<String> items = List.of("coin", "ball", "lamp", "spoon");
items.forEach(System.out::println);
}
In the example we loop over the elements with the forEach method.
Source
In this article we have looked at the brief history of element iteration in Java.
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