COLLECTIONS IN JAVA

 Collections in Java

• FRAMEWORKS
• ADVANTAGES OF JAVA COLLECTION FRAMEWORK
• METHODS OF COLLECTION INTERFACE
• LINKED LIST
• VECTOR
• STACK
• QUEUE INTERFACE
• SET INTERFACE
• CLASSES THAT IMPLEMENT THE SET INTERFACE( HARSH SET, SORTED SET, MAP, ETC)

Java's Collection framework may be used to store and manage collections of objects.

Java Collections may be used for data operations such as sorting, searching, inserting, modifying, and removing. In Java, an object collection is called a collection. The Java Collection foundation includes classes and interfaces including Vector, LinkedList, Priority Queue, HashSet, LinkedHashSet, and TreeSet.

Framework in Java

An architecture that has already been created for a group of classes and interfaces is called a framework. It is not necessary to define a framework to add a new class or function. But with a perfect object-oriented design, there is always a framework with classes in it, so every class does the same job.

Java's unique collection structure is required

Arrays, vectors, and hash tables were the usual Java ways for objects (or collections) before the introduction of the collection framework (or JDK 1.2). All of these collections lacked a single, cohesive user interface. As a result, even while every collection aims to achieve the same general objective, each collection's implementation was decided upon independently of the others. Not to mention how hard it is for users to remember the distinct constructors, functions, and syntax of every collection class.

A nice example of this is the procedure for adding an element and a vector to a hash table.

Let's see an example here:

// why collection framework was needed

The Array, Vector, and Hash table collections had a standard member interface, which made it hard for programmers to design algorithms that could manage several types of collections. Another disadvantage is that since the majority of the 'Vector' methods are final, therefore we can't modify the 'Vector' class to create an equivalent collection. As a result, the Java development team created the Collection Framework in JDK 1.2 as a common interface to handle the aforementioned problems; this framework was used to standardize both the hash table and the outdated vectors.

Advantages of Java collection framework

Since the aforementioned disadvantages stem from the absence of a collecting framework, the following are advantages of having one.

When all classes that implement an application programming interface (API) utilize the same set of methods, that API is said to be consistent. This comprises, among other things, Set, LinkedList, Vector, and ArrayList.

reduces the developer's workload on the code by letting him focus on using the collection as efficiently as can rather than thinking about how it was designed. This successfully implements the core concept or features of object-oriented programming, which is sometimes referred to as abstraction.

Enhances the effectiveness and caliber of the program Since algorithms and data structures are supplied in a useful and efficient way—the programmer is not performing their job here—performance is enhanced. It is essential to think about how best to use a certain data structure. All he needs to do is employ the best implementation to significantly increase the efficiency of his algorithm or program.

Methods of collection interface

Collection interface

The collection interface is followed by every class that comprises the collection framework. It spells out how each set is to be done. Stated differently, a collection interface creates the basis upon which the entire framework is built.

Every subclass implements many of the methods available in the collection interface. void clean (), Boolean add All (Collection c), and Object obj are a few of these methods.

List interface

The list interface is a subset of the overall interface. These blocks allow us to store an ordered collection of items in a list-type data structure. It can hold several values in storage.

The List interface is implemented by the classes ArrayList, LinkedList, Vector, and Stack. One cannot construct the List interface without first using it.

1. List <data-type> list1= new ArrayList();  
2. List <data-type> list2 = new LinkedList();  
3. List <data-type> list3 = new Vector();  
4. List <data-type> list4 = new Stack(); 

 

Iterable interface

The primary interface via which all collection classes communicate with one another is the Iterable interface. All Aggregate subclasses implement the Iterable interface as the aggregate interface is an extension of the Iterable interface.

It has just one abstract method. in other words,

Iterator<T> iterator ()

Iterator interface

The Iterator UI provides the ability to iterate elements forward only.

Iterator UI Methods The Iterator UI has only three methods. They are: 

Array list

We can access dynamic arrays using Java thanks to the ArrayList class. It may operate more slowly than traditional arrays, but in high-traffic scenarios, it can be helpful. An ArrayList's count automatically increases as new members are added, and it automatically decreases when elements are removed. Java ArrayList allows for random access to the list. Older data types that are incompatible with ArrayList include char, int, and so on. In these cases, you need a wrapper class.

Let's understand ArrayList with the below example.

// Below Java program to show how the ArrayList works

Linked list

One technique to build the linear LinkedList data structure is with the LinkedList class. It handles each element as an individual object with data and an address component, and stores items in non-contiguous places. The parts are linked via pointers and addresses. A node is an individual component.

Let's use the following example to better understand Linked Lists.

let us try with an example:

// Below program to show the working of LinkedList in Java

Vector

In Java, we may access dynamic arrays via a vector. It may work slower than regular arrays, but it may be useful for systems that need to manipulate arrays extensively. The implementation of this is the same as that of ArrayList. But the main distinction between an array list and a vector is that the former is non-synchronized while the latter is.

Let's use an example to better grasp the Vector.

// Below program to shows the working of Vector in Java

// working of Vector

Stack

The stack data structure is implemented and modeled by the Stack class. The last-in, first-out policy governs the class. This class additionally has the empty, search, and peek methods in addition to the regular push and pop methods. Another name for the class is the Vector subclass.

Let's use an example to better grasp the stack.

// Below program to shows the working of a stack in Java

// working of a stack

Queue interface

The queue interface follows the First In First Out (FIFO) protocol, much like a real queue would. This interface can handle all of the components if the order is important. Every time we try to book a ticket, we witness this in action because there are relatively few available. As a result, the ticket will be given to the person whose request is next in line. There are several classes available, including Array-Deque and Priority-Queue. Since all of these subclasses implement Queue, if we want or need then we can use any of them to construct a Queue object.

1. Queue<String> q1 = new PriorityQueue();  
2. Queue<String> q2 = new ArrayDeque();

 

Priority queue

When processing items depending on their priority, a priority queue is used. The Priority-Queue class is used when processing the queue's items based on priority is necessary, even if it is widely known that the queue runs on a First-In, First-Out basis. Priority-Queue is fundamentally a priority queue. The priority queue items are sorted using either the Comparator that is specified when the queue is established or by natural order, depending on which constructor was used.

By understating the below code we can also understand the priority queue:

// priority queue in Java

Deque interface

In this instance, the Queue data structure has undergone some modification. Double queues are another type of data structure that is similar to a queue, let us add and delete bits from both ends. Compared to the queue interface, this interface is superior. The Array-Deque class makes use of this interface. We may create a deque object by implementing the Deque interface with the help of the Array-Deque class.

Deque d = new ArrayDeque();

Array deque

Array-Deque is a class that complies with the Deque specification. Deque's use is made easier by this. In contrast to a queue, we can add and remove things from both ends.

There is no size restriction for Array-Deque, and it is quicker than ArrayList and Stack.

Let’s look at the below code example.

Set interface

An array is a non-recursive set of items that prevents duplicate data from being stored. We use this collection when we wish to preserve only unique things in our collection and not any that overlap. This set interface is used by numerous classes, such as LinkedHashSet, TreeSet, HashSet, and many more. Since all of these classes implement a set, you may use any of them to create a set object.

For example.

Set<data-type> s1 = new HashSet<data-type>();  

Set<data-type> s2 = new LinkedHashSet<data-type>();  

Set<data-type> s3 = new TreeSet<data-type>();

Classes that implement the set interface

Harsh-set

The HashSet class, a private variant of the hash-table data structure, is utilized inside. It cannot be guaranteed that elements that are addable to a hash set will be added in a predetermined sequence. Every item is placed based on its hash code. Additionally, NULL objects are allowed in this class. To help you understand HashSet, consider this example.

// working of a HashSet

Sorted set interface

This interface and the fixed interface have several things in common. The only way this interface is different is that it offers additional techniques for maintaining element order. The Sorted-Set interface extends the Set interface to provide a more convenient way to handle sorted data. Without the TreeSet class, you cannot construct this interface. Since this class is an implementation of Sorted-Set, Sorted-Set instances can be created using it.

SortedSet<data-type> set = new TreeSet();

Tree set

What the TreeSet class uses is a storage tree. The array will use the elements' natural order to maintain order whether or not an explicit comparator is provided. If the set interface is incompatible with its peers, it cannot be implemented correctly. It can also be purchased with a Comparator that is meant to be delivered at a certain construction time, depending on the builder. An example will help you better understand TreeSet.

Map interface

A map is one tool for organizing data that lets you work with key-value pairs. This interface does not support duplicate keys since a single key cannot have multiple mappings. Nevertheless, duplicate values can exist for separate keys. The map comes in helpful when the data is already available and we want to use the key to conduct actions. Many classes implement this Map interface, such as HashMap, Tree-Map, and others. All of these classes implement Map, thus we can use any of them to generate a Map object.

Map<T> hm = new HashMap<> (); 

Map<T> tm = new TreeMap<> ();

 

Where T is the type of the object

Hash map

HashMap offers a basic Java implementation of the map interface. Data is stored using pair notation (key, value). To retrieve the value of a hash map, we must know its key. HashMap employs the hashing method. Hashing may be used to break up large strings into smaller ones that nonetheless represent the same string for more effective indexing and search operations. HashMap is also used internally by HashSet. Let's examine HashMap as an illustration.