Java Collections Framework for Beginners | Realtime examples

Collections framework is one of the most valuable and exciting topics in the Java language.

So why do you think we need Java collections? The Java collection framework provides the developers with access to prepackaged data structures as well as algorithms to manipulate data.

This Java collections framework blog will cover the following topics in depth.

Java collections can be defined as a group of objects. A collection is usually a single unit consisting of more than one object. You can perform all operations on data such as searching, sorting, insertion, manipulation, deletion, etc. by Java collections.

A framework is software that has a ready-made functional interface or architecture and also contains a set of classes and interfaces to be used with the provided interface.

Let’s understand it with some real-time examples.

1. In childhood, you had a kiddy bank. In the kiddy bank, you had collected a lot of coins. This kiddy bank is called collection and the coins are nothing but objects.

2. During school time, you put all the important books in the school bag before going to school. Here Schoolbag is a collection and books are objects.

3. A classroom is a collection of students. So, the classroom is nothing but a collection and students are objects.

4. We know that the entire world is a collection of humans, animals, and different things. The world is a collection and humans, animals and different things are different objects.

Technically, a collection is an object or container which stores a group of other objects as a single unit or single entity. Therefore, it is also known as a container object or collection object in java.

A container object means it contains other objects. In simple words, a collection is a container that stores multiple elements together.

JVM (Java Virtual Machine) stores the reference of other objects into a collection object. It never stores physical copies of other objects because other objects are already available in the memory and storing another copy of objects into a collection object would be a wasting of memory.

A group of objects stored in a collection object is shown in the below figure. In the figure, we are storing 5 objects in a collection object.

A simple example of a collection is given below:

The hierarchy of the entire collection framework consists of four core interfaces such as Collection, List, Set, Map, and two specialized interfaces named SortedSet and SortedMap for sorting.

All the interfaces and classes for the collection framework are located in java. util package. The diagram of the Java collection hierarchy is shown in the below figure.

These are the 5 key interfaces of the collection framework which we can use according to our use.

Although the java Map interface is a Java Collection framework. It doesn’t inherit from the Java Collection framework. Instead, it has its own interface hierarchy that maintains key-value pairs.

There are three components that extend the collection interface i.e List, Queue and Sets. Let’s learn about them in detail:

Example 1: A simple example of List Interface using ArrayList

import java.util.*;
 public class ListInterface{
  public static void main(String args[]){
 
  //Creating a List
  List<String> list=new ArrayList<String>();
 
  //Adding elements in the List
  list.add("Ford");
  list.add("Tata");
  list.add("Mahindra");
  list.add("Suzuki");
  list.add("Honda");
 
  //Iterating the List element using for-each loop
  for(String Vehicle:list) {
  System.out.println(Vehicle);
 
  }
  }

}

Output

Ford
  Tata
  Mahindra
  Suzuki
  Honda

Example 2: A simple example of Set Interface using HashSet

import java.util.HashSet;

import java.util.Set;

public class SetInterface {

public static void main(String[] args) {

//creating set

Set<String> set = new HashSet<String>();

//Adding elements in the Set

set.add("Ford");

set.add("Tata");

set.add("Mahindra");

set.add("Suzuki");

set.add("Honda");

//Iterating the Set element using for-each loop

for(String vehicle:set) {

System.out.println(vehicle);

}

}

}

Output

Mahindra
  Suzuki
  Ford
  Tata
  Honda

Difference between HashMap, Treemap, LinkedHashMap, and HashTable:

Example: Basic program of map interface in Java

import java.util.HashMap;

class Main {

public static void main(String[] args) {

// create a hashmap

HashMap<String, Integer> languages = new HashMap<>();

// add elements to hashmap

languages.put("Java", 8);

languages.put("C", 11);

languages.put("C++", 9);

languages.put("Python", 5);

System.out.println("HashMap elements : " + languages);

}

}

Output

HashMap elements : {Java=8, C++=9, C=11, Python=5}

#1) What is the use of a collection framework in Java?

Answer: The collection framework offers prepackaged algorithms, interfaces, and classes that allow programmers to write highly efficient programs that can store and process data.

#2) What is Java Collections API in Java?

Answer: The Java collections API provides interfaces and classes that can be extended and implemented in order to use data structures that are nothing but collections.

Conclusion

This blog gave us an introduction to the Java Collections Framework.

I hope this blog explained most of the topics in the Java collections framework, its hierarchy, interface, list, queue, and sets that I have discussed above. Please share your opinion with comments.