Java is a simple programming language. Java makes it straightforward to write, compile, and debug programming. It helps to make reusable code and modular programs. Java is a universal programming language built for developers to write at runtime where Java code is compiled, it can operate on all platforms supporting Java. Java applications are compiled into bytecodes that can run on any Java Virtual Machine. The syntax of Java is similar to c/c++.
 
This blog will cover collections in Java and how to implement them.
 

Collections in Java


"      Java Collection Framework
"      Hierarchy Collection Framework
"      Collection interface
"      Iterator interface

A collection in Java is a framework that provides an architecture for storing and manipulating a group of objects.
Java collections can perform all the operations you perform on data, such as searching, sorting, inserting, manipulating, and deleting.
A Java Collection means a single unit of objects. The Java Collection framework furnishes multiple interfaces (Set, List, Queue, Deque) and classes (ArrayList, Vector, LinkedList, PriorityQueue, HashSet, LinkedHashSet, TreeSet).
 
The collection framework is a suitable architecture for defining and manipulating collections. All collection frames include the following:
Interfaces: These are notional data types that describe collections. Interfaces allow groups to be manipulated independently of the details of their representation.
Implementations, i.e., classes ? These are specific implementations of collection interfaces. Basically, these are reusable data structures.
Algorithms: These methods perform valuable computations on objects that implement collection interfaces, such as searching and sorting. Algorithms are declared polymorphic: the same technique can be applied to various implementations of the relevant collection interface.

Java Development Training

By Industry Expert
Explore Course
Now you are probably wondering what a framework is. So let's understand what a framework is.
 

What is a framework?


A framework is a pack of classes and interfaces that deliver a finished architecture. There is no demand to specify a framework to implement a new function or class. However, optimal object-oriented design always includes a framework with a collection of classes so that all classes perform the same task.
 

Why do we need a different collection framework?


Before the Collection Framework (or JDK 1.2), the standard methods for grouping Java objects (or collections) were Arrays Vectors or Hashtables. All these collections had no standard interface. Therefore, even though the primary goal of all groups is the same, the enactment of all these collections was determined independently and had no correlation. And it's also challenging for users to remember all the different methods, syntax, and constructors in each collection class.
 

Advantages of the Collection Framework:


Since the scarcity of a collection framework has offered rise to the above set of disadvantages, here are the advantages of the collection framework.
 
Consistent API: An API has a core set of interfaces like Collection, Set, List, or Map, all classes (ArrayList, LinkedList, Vector, etc.) that implement these interfaces have some standard set of methods.
 
Reduces programming effort: The programmer does not have to worry about the collection's design. But instead, he can focus on making the best use of it in his program. Therefore, the fundamental concept of object-oriented programming (i.e., abstraction) was successfully implemented.
 
Increases program speed and quality: Increases execution by providing high-performance implementations of functional data structures and algorithms since the programmer does not have to think about the best implementation of a particular data structure. He can easily use the best performance to drastically increase the performance of his algorithm/program.

Java Programming

By Industry Expert
Explore Course

 

Collection interface methods


This interface contains various methods that can be used directly by all collections implementing this interface. They are:
 
add(Object): This mode is used to add an object to the collection.
addAll(Collection c): This process adds all the elements in the given collection to this collection.
clear(): This approach removes all elements from this collection.
contains(Object o): This approach returns true if the collection contains the specified element.
containsAll(Collection c): This procedure returns true if the collection contains all the elements in the given collection.
equals(Object o): This technique compares the specified object with this collection for equality.
hashCode() : This approach returns the hash code value for this collection.
isEmpty() : This process returns true if this collection contains no elements.
iterator() : This approach returns an iterator over the elements in this collection.
max() : This procedure returns the maximum value present in the collection.
parallelStream() : This method returns a parallel stream with this collection as its source.
remove(Object o) : This method removes the given entity from the collection. If there are same values, then this method will remove the first occurrence of the thing.
removeAll(Collection c) : This method removes all objects listed in the given collection from the collection.
removeIf(Predicate filter) : This method removes all elements of this collection that satisfy the given predicate.
keepAll(Collection c) : This method is used to keep only the elements in this collection that are contained in the specified collection.
size() : This approach returns the number of elements in the collection.
spliterator() : This method is used to create a Spliterator over the elements in this collection.
stream() : This approach returns a sequential Stream with this collection as its origin.
toArray() : This process returns an array containing all elements in this collection.
 
Now let's discuss a collection of java interview questions.
 
1. How would you convert ArrayList to Array and Array to ArrayList?
An array can be converted to an ArrayList using the asList() was provided by the Array class. It is a static approach that accepts list objects as a parameter.
Syntax:
```
Arrays.asList(item)
```
An ArrayList can be transformed to an Array using the toArray() method of the ArrayList class.
Syntax:
```
            List_object.toArray(new String[List_object.size()])
```
 
2. How do you change the list?
An ArrayList can be reversed using the reverse() method of the Collections class.
Syntax:
```
            public static void reverse(Collection c)
```
For Example:
```
 public class ReversingArrayList {
       public static void main(String[] args) {
                   List myList = new ArrayList();
                   myList.add("AWS");
                   myList.add("Java");
                   myList.add("Python");
                   myList .add("Blockchain");
                   System.out.println("Before Reversing");
                   System.out.println(myList.toString());
                   Collections.reverse(myList);
                   System.out.println("After Reversing");
                   System.out.println(myList);
       }
  }
 
3. Explain equals() with an example
Equals() check whether the number object is equal to the object passed as an argument or not.
The syntax of the equals() method is:
```
public boolean equals(Object o)
```
This method takes two parameters 1) an arbitrary object and 2) a return value. Returns true if the argument passed is not null and is an object of a similar type with the same numeric value.
Example:

Import java.lang.Integer;
public class Test {
   public static void main(String args[]) {
      Integer p = 5;
      Integer q = 20;
      Integer r =5;
      Short s = 5;
      System.out.println(p.equals(q));
      System.out.println(p.equals(r));
      System.out.println(p.equals(s));
   }
}
 
4. List the advantages of a generic collection
The benefits of using a generic collection are:
"      If programmers use generic classes, they do not require type casting.
"      It is type-safe and can be checked at compile time.
"      It provides code stability by detecting errors at compile time.
 
5. Define BlockingQueue
BlockingQueue is an interface that utilizes in Java that can extend a queue. It delivers concurrency in various queue operations like fetch, insert, delete, etc.
The queue waits until it is empty when loading any elements. BlockingQueue should not contain null elements. The execution of this queue is thread-safe.
The BlockingQueue syntax is:
```
public interface BlockingQueue extends Queue
```

Summary


The Java collection framework provides the programmer access to prepackaged data structures and algorithms for manipulating them.
A collection is an object that can contain references to other things. Collection interfaces declare the functions that can be executed on each type of collection.
Collection framework classes and interfaces are in the java.util package.