Collection traversal tool: the secret of Java Iterator and Iterable

Java Iterator and Iterable are two key interfaces used to traverse collections in JavaCollectionsFramework. They provide a simple and unified way to access the elements in a collection without directly manipulating the collection itself. In this article, we'll take a deep dive into Iterator and Iterable and show how to use them to simplify collection traversal with demo code.

Iterator interface

Iterator is an interface that defines methods for iterating elements in a collection. It provides four methods to traverse collections:

• hasNext(): Check whether there are still elements in the collection.
• next(): Returns the next element in the collection.
• remove(): Remove the current element from the collection.
• forEachRem<strong class="keylink">ai</strong>ning(Consumer<? super E> act<strong class="keylink">io</strong>n): Perform an operation on the remaining elements in the collection.

The Iterator interface is usually used with the Iterator() method of a collection, which returns an Iterator object that can be used to traverse the elements in the collection. For example, the following code shows how to use an Iterator to traverse an ArrayList:

List<String> names = new ArrayList<>();
names.add("John");
names.add("Mary");
names.add("Bob");

Iterator<String> iterator = names.iterator();
while (iterator.hasNext()) {
String name = iterator.next();
System.out.println(name);
}

Output:

List<String> names = new ArrayList<>();
names.add("John");
names.add("Mary");
names.add("Bob");

for (String name : names) {
System.out.println(name);
}

Output:

John
Mary
Bob

The difference between Iterator and Iterable

Iterator and Iterable are both interfaces for traversing collections, but there are some key differences between them:

• Iterator is an instance interface, which means it must be implemented by a collection class. Iterable is a type interface, which means it can be implemented by any class, including collection and non-collection classes.
• Iterator provides richer functions than Iterable because it provides the remove() method and the forEachRemaining() method. Iterable only provides the iterator() method.
• Iterator is usually used with while loops, while Iterable is usually used with enhanced for loops.

in conclusion

Java Iterator and Iterable are two key interfaces in the Java collection framework for traversing collections. They provide a simple and unified way to access the elements in a collection without directly manipulating the collection itself. Iterator provides richer functionality than Iterable, but Iterable is easier to use.

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