What is the difference between HashSet and ArrayList?

ArrayList maintains the insertion order i.e order of the object in which they are inserted. HashSet is an unordered collection and doesn't maintain any order. ArrayList allows duplicate values in its collection. On other hand duplicate elements are not allowed in Hashset.

Is HashSet faster than ArrayList?

As a conclusion, we can learn, that the contains() method works faster in HashSet compared to an ArrayList.

Does HashSet extend ArrayList?

Ordering : HashSet is an unordered collection and doesn't maintain any order while ArrayList maintains the order of the object in which they are inserted. 4. Duplicates : HashSet doesn't allow duplicates though ArrayList allows duplicate values.


What is difference between Set and list?

List is an ordered sequence of elements whereas Set is a distinct list of elements which is unordered.

Which is better ArrayList or HashMap?

ArrayList stores the elements only as values and maintains internally the indexing for every element. While HashMap stores elements with key and value pairs that means two objects. So HashMap takes more memory comparatively.


Java Interview Questions #76 - What is the difference between ArrayList and HashSet?



Which collection is faster in Java?

If you need fast access to elements using index, ArrayList should be choice. If you need fast access to elements using a key, use HashMap. If you need fast add and removal of elements, use LinkedList (but it has a very poor seeking performance).

Can ArrayList have duplicates?

ArrayList allows duplicate values while HashSet doesn't allow duplicates values. Ordering : ArrayList maintains the order of the object in which they are inserted while HashSet is an unordered collection and doesn't maintain any order.

What is Polymorphism in Java?

Polymorphism means "many forms", and it occurs when we have many classes that are related to each other by inheritance. Like we specified in the previous chapter; Inheritance lets us inherit attributes and methods from another class. Polymorphism uses those methods to perform different tasks.

What is difference between iterator and ListIterator?

An Iterator is an interface in Java and we can traverse the elements of a list in a forward direction whereas a ListIterator is an interface that extends the Iterator interface and we can traverse the elements in both forward and backward directions.


Does HashSet allow duplicates?

Duplicates: HashSet doesn't allow duplicate values. HashMap stores key, value pairs and it does not allow duplicate keys. If the key is duplicate then the old key is replaced with the new value.

What is the difference between HashSet and list?

ArrayList maintains the insertion order i.e order of the object in which they are inserted. HashSet is an unordered collection and doesn't maintain any order. ArrayList allows duplicate values in its collection. On other hand duplicate elements are not allowed in Hashset.

Does HashSet allow null values?

Null values in HashSet − The HashSet object allows null values but, you can add only one null element to it. Though you add more null values if you try to print its contents, it displays only one null.

Which is the best collection in Java?

Java Collections – Set

HashSet, which stores its elements in a hash table, is the best-performing implementation; however it makes no guarantees concerning the order of iteration. TreeSet, which stores its elements in a red-black tree, orders its elements based on their values; it is substantially slower than HashSet.


Is HashSet faster than set?

Performance. Simply put, HashSet is faster than the TreeSet. HashSet provides constant-time performance for most operations like add(), remove() and contains(), versus the log(n) time offered by the TreeSet. Usually, we can see that the execution time for adding elements into TreeSet is much more than for the HashSet.

What is difference between list set and map?

The main difference between the List and Set interface in Java is that List allows duplicates while Set doesn't allow duplicates. All implementation of Set honor this contract. While a Map holds two objects per Entry e.g. a key and a value and It may contain duplicate values but keys are always unique.

What is difference between overriding and overloading?

What is Overloading and Overriding? When two or more methods in the same class have the same name but different parameters, it's called Overloading. When the method signature (name and parameters) are the same in the superclass and the child class, it's called Overriding.

Can we override static method?

Overloading is the mechanism of binding the method call with the method body dynamically based on the parameters passed to the method call. Static methods are bonded at compile time using static binding. Therefore, we cannot override static methods in Java.


What is abstract in Java?

Abstract class: is a restricted class that cannot be used to create objects (to access it, it must be inherited from another class). Abstract method: can only be used in an abstract class, and it does not have a body. The body is provided by the subclass (inherited from).

Why Hashmap is not part of collection?

Because they are of an incompatible type. List, Set and Queue are a collection of similar kind of objects but just values where a Map is a collection of key and value pairs.

What is difference between collection interface and collection class?

The Collection interface provides the standard functionality of data structure to List, Set, and Queue. However, Collections class is to sort and synchronize the collection elements.

What is static method in Java?

In Java, a static method is a method that belongs to a class rather than an instance of a class. The method is accessible to every instance of a class, but methods defined in an instance are only able to be accessed by that object of a class.


Can ArrayList be resized?

Since ArrayList is a growable array, it automatically resizes itself whenever a number of elements in ArrayList grow beyond a threshold. However, ensureCapacity() method of java.

Is Vector synchronized?

Synchronization: Vector is synchronized, which means only one thread at a time can access the code, while ArrayList is not synchronized, which means multiple threads can work on ArrayList at the same time.

What is collections API in Java?

The Java Collections API provide Java developers with a set of classes and interfaces that makes it easier to work with collections of objects, e.g. lists, maps, stacks etc. Rather than having to write your own collection classes, Java provides these ready-to-use collection classes for you.
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