Question: How Do I Iterate Through Collections?

How do you iterate over an ArrayList?

The iterator can be used to iterate through the ArrayList wherein the iterator is the implementation of the Iterator interface.

Some of the important methods declared by the Iterator interface are hasNext() and next()..

What are the two ways to iterate the elements of a collection?

There are three common ways to iterate through a Collection in Java using either while(), for() or for-each(). While each technique will produce more or less the same results, the for-each construct is the most elegant and easy to read and write.

How do you access elements in an ArrayList?

Learn how to get the element from an ArrayList….1. ArrayList get() method1.1. get() Syntax. indexOf() method. public Object get( int index );1.2. get() Parameter. index – index of the element to return. … 1.3. get() Return Value. The get() method returns the reference of the object present at the specified index.

What method do you need to call to get an iterator over a collection?

Obtain an iterator to the start of the collection by calling the collection’s iterator( ) method. Set up a loop that makes a call to hasNext( ). Have the loop iterate as long as hasNext( ) returns true. Within the loop, obtain each element by calling next( ).

What is the difference between ArrayList and LinkedList classes in collection framework?

LinkedList uses Doubly Linked List to store its elements. ArrayList is slow as array manipulation is slower. LinkedList is faster being node based as not much bit shifting required. ArrayList implements only List.

What iterator can throw a ConcurrentModificationException?

Using an Iterator The iterators returned by ArrayList iterator() and listIterator() methods are fail fast: if the list is structurally modified at any time after the iterator is created, in any way except through the iterator’s own remove or add methods, the iterator will throw a ConcurrentModificationException.

How do you iterate through a list?

There are 7 ways you can iterate through List.Simple For loop.Enhanced For loop.Iterator.ListIterator.While loop.Iterable.forEach() util.Stream.forEach() util.

How do you iterate a set?

Iterating over Set using IteratorObtain the iterator by calling the iterator() method.You can use while or for loop along with hasNext(), which return true if there are more elements in the Set.Call the next() method to obtain the next elements from Set.

What does iterator do in Java?

An Iterator is an object that can be used to loop through collections, like ArrayList and HashSet. It is called an “iterator” because “iterating” is the technical term for looping. To use an Iterator, you must import it from the java.

What is JSONObject class in Java?

JsonObject class represents an immutable JSON object value (an unordered collection of zero or more name/value pairs). It also provides unmodifiable map view to the JSON object name/value mappings. A JsonObject instance can be created from an input source using JsonReader. readObject() .

How can you avoid ConcurrentModificationException while iterating a collection?

To Avoid ConcurrentModificationException in multi-threaded environmentYou can convert the list to an array and then iterate on the array. … You can lock the list while iterating by putting it in a synchronized block. … If you are using JDK1.

How do you iterate a JSON object in Python?

Use json. loads() and a for-loop to iterate through a JSON string. Call json. loads(str) to parse a JSON string str to a Python dictionary.

How do I iterate through a JSONArray?

getJSONObject(“JObjects”); JSONArray getArray = getObject. getJSONArray(“JArray1”); for(int i = 0; i < getArray. size(); i++) { JSONObject objects = getArray. getJSONArray(i); //Iterate through the elements of the array i. //Get thier value. //Get the value for the first element and the value for the last element. }

Is ArrayList thread safe?

ArrayList , on the other hand, is unsynchronized, making them, therefore, not thread safe. With that difference in mind, using synchronization will incur a performance hit. So if you don’t need a thread-safe collection, use the ArrayList .

Can we modify collection while iterating?

Do not modify the underlying collection when an iteration is in progress. According to the Java API documentation [API 2014] for the Iterator. remove() method: … It is not generally permissible for one thread to modify a Collection while another thread is iterating over it.