Java Interview Questions SET-01

Java Interview Questions Set-02 ARRAY

Java Interview Questions Set-03 MAP

Java Interview Question Set-04

Explain Array, List and Map with Examples?

Array: Imagine you have a collection of toys that you want to keep in a row. An array is like a long shelf with compartments. Each compartment can hold one toy. You can count the toys by looking at how many compartments are filled. You can also take out a specific toy by knowing its position on the shelf.
List: Now, think of a list as a collection of toys that you can put in any order. It's like having a bag where you can put in or take out toys whenever you want. With a list, you don't have to worry about a specific order. You can add more toys to the list or remove them as you like.
Map: Imagine you have a box full of different colored balls, and each ball has a name written on it. A map is like a magical box that helps you find a ball by its name. You can ask the box to give you a ball with a specific name, and it will find it for you. In a map, you can store pairs of names and balls, and easily find the ball you need by looking up its name.

Remember, an array is like a shelf, a list is like a bag, and a map is like a magical box to help you find things. Each one is useful in different situations, depending on how you want to organize or find your toys or objects in Java programming.

What are the most important necessary libraries? [Knowledge]

import java.util.ArrayList;

import java.util.HashMap;

import java.util.List;

import java.util.Map;

How to Declaring and initializing an array[Knowledge]

String[] myArray = {"element1", "element2", "element3"};

What are the different ways to call a method in Java? <- Must Know

How to Declaring and initializing a list:

List<String> myList = new ArrayList<>();
myList.add("element1");
myList.add("element2");
myList.add("element3");

How to add/join/combine two ArrayList ?

: Refer to the link HERE for answers with the code.

How to Declaring and initializing a map:

Map<String, Integer> myMap = new HashMap<>();
myMap.put("key1", 1);
myMap.put("key2", 2);
myMap.put("key3", 3);

How to Sort a Hashmap in Java?

Ans: Refer to the link HERE for answer with code.

How to Access elements in an array:

String firstElement = myArray[0];

String secondElement = myArray[1];

How to Access elements from the list:

String firstElement = myList.get(0);

String secondElement = myList.get(1);

How do I find duplicate elements and count the same using Map in Java?

Refer to the link HERE for answers with code

How to Access elements in a map?

int valueForKey1 = myMap.get("key1");

int valueForKey2 = myMap.get("key2");

How do you iterate over an array?

for (String element : myArray)

{

System.out.println(element);

}

How do you iterate over the list?

for (String element : myList)

{

System.out.println(element);

}

Learn about Strings with Multiple Choice Q&A <- Must Know

How do you iterate over a map?

for (Map.Entry<String, Integer> entry : myMap.entrySet())

{

String key = entry.getKey();

int value = entry.getValue();

System.out.println("Key: " + key + ", Value: " + value);

}

What are the main performance differences between Array and List?

In Java, there are performance differences between arrays and lists due to their underlying implementations.

Memory Allocation: Arrays have a fixed size that is determined at the time of creation. This allows for efficient memory allocation as the required memory for all elements is allocated in a contiguous block. On the other hand, lists such as ArrayList dynamically resize themselves as elements are added or removed. This resizing process may involve creating a new array and copying elements, resulting in potential memory overhead.
Random Access: Arrays provide fast random access to elements by index. Since arrays have a fixed size and a known memory layout, accessing an element at a specific index is a constant-time operation (O(1)). In contrast, lists implemented as linked structures, such as LinkedList, require traversing the list from the beginning to reach a specific index, resulting in a linear-time operation (O(n)).
Insertion and Deletion: Arrays are efficient for adding or removing elements at the ends, as it involves shifting or resizing the underlying array. Adding or removing elements at the beginning or in the middle of an array requires shifting the subsequent elements, resulting in a time complexity of O(n). Lists, especially LinkedList, are more efficient for frequent insertion and deletion operations as they only require updating references between nodes.
Iteration: Iterating over an array using a simple for loop is generally faster compared to iterating over a list using an iterator or enhanced for loop. This is because arrays provide direct memory access to elements, while lists may involve traversing internal structures.

Overall, arrays tend to have better performance for random access and predictable-sized collections, while lists offer more flexibility for dynamic resizing, insertion, and deletion. The choice between them depends on the specific use case and the operations required in your application.

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