Java Iterator Interface

In this tutorial, we will learn about the Java Iterator interface through an example.

The Iterator interface of the Java collection framework allows us to access the elements of the collection. It has a subinterface called ListIterator.

All Java collections include an iterator() method. This method returns an iterator instance used to iterate over the elements of the collection.

Iterator methods

The Iterator interface provides4This method, which can be used to perform various operations on collection elements.

• hasNext() - Return true if there is an element in the collection

• next() - Return the next element of the collection

• remove() -Remove the last element returned by next()

• forEachRemaining() - Perform the specified operation on each remaining element of the collection

Example: Implementation of Iterator

In the following example, we implement the hasNext(), next(), remove(), and forEachRemaining() methods of the Iterator interface in an array list.

import java.util.ArrayList;
import java.util.Iterator;
class Main {
　　　　public static void main(String[] args) {
　　　　　　　　//Creating an ArrayList
　　　　　　　　ArrayList<Integer> numbers = new ArrayList<>();
　　　　　　　　numbers.add(1);
　　　　　　　　numbers.add(3);
　　　　　　　　numbers.add(2);
　　　　　　　　System.out.println("ArrayList: "}　+　numbers);
　　　　　　　　//Creating an instance of Iterator
　　　　　　　　Iterator<Integer> iterate = numbers.iterator();
　　　　　　　　//Using the next() method
　　　　　　　　int number = iterate.next();
　　　　　　　　System.out.println("Accessing element: "}　+　number);
　　　　　　　　//Using remove() method
　　　　　　　　iterate.remove();
　　　　　　　　System.out.println("Delete Element: ");　+　number);
　　　　　　　　System.out.print("Updated ArrayList: ");
　　　　　　　　//Using hasNext() method
　　　　　　　　while(iterate.hasNext()) {
　　　　　　　　　　　　//Using forEachRemaining() method
　　　　　　　　　　　　iterate.forEachRemaining((value　-> System.out.print(value　+　", "
　　　　　　　　}
　　　　}
}

Output Result

ArrayList: [1,　3,　2]
Access Element:　1
Delete Element:　1
Updated ArrayList:　3,　2,

In the above example, please note the following statement:

iterate.forEachRemaining((value　-> System.put.print(value　+　", "

In this example, we willLambda ExpressionPassed as a parameter to the forEachRemaining() method.

Now, this method will print all the remaining elements in the array list.