EC Tutorials

Iterator is something that can be used to connect to collections, such as ArrayList and HashSet. It is called "iterator" because "iterating" is a technical term for unlocking.

To use Iterator, you must import it into a java.util package.

Getting an Iterator

The iterator() method can be used to get an Iterator for any collection:

Example

// Import the ArrayList class and the Iterator class
            import java.util.ArrayList;
            import java.util.Iterator;
            
            public class Main {
              public static void main(String[] args) {
            
                // Make a collection
                ArrayList<String> cars = new ArrayList<String>();
                cars.add("Volvo");
                cars.add("BMW");
                cars.add("Ford");
                cars.add("Mazda");
            
                // Get the iterator
                Iterator<String> it = cars.iterator();
            
                // Print the first item
                System.out.println(it.next());
              }
            }

Looping Through a Collection

To navigate the collection, use the hasNext() and the following Iterator modes:

Example

while(it.hasNext()) {
            System.out.println(it.next());
          }

Removing Items from a Collection

Iterators are designed to easily change the collections you enter. The remove() method can remove items from the collection while looping.

Example

Use an iterator to remove numbers less than 10 from a collection:

import java.util.ArrayList;
            import java.util.Iterator;
            
            public class Main {
              public static void main(String[] args) {
                ArrayList<Integer> numbers = new ArrayList<Integer>();
                numbers.add(12);
                numbers.add(8);
                numbers.add(2);
                numbers.add(23);
                Iterator<Integer> it = numbers.iterator();
                while(it.hasNext()) {
                  Integer i = it.next();
                  if(i < 10) {
                    it.remove();
                  }
                }
                System.out.println(numbers);
              }
            }

Note: Trying to delete items using each for loop or a for-each loop will not work properly because the cluster changes size at the same time as the code tries to loop.

Previous Next

Java Iterator

Java Iterator

Getting an Iterator

Example

Looping Through a Collection

Example

Removing Items from a Collection

Example

TUTORIALS

REFERENECES

EXAMPLES

© copyright 2021. All rights reserved.