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.
Let's start by explaining the concept of a loop and then explore how it can be used with arrays, lists, and maps.
A loop is a programming construct that allows you to repeatedly execute a block of code. It is useful when you need to perform a certain operation multiple times or iterate over a collection of items. There are different types of loops, but the most common ones are the "for" loop and the "while" loop.
What are the different ways to call a method in Java? <- Must Know
Looping around an array:
An array is a data structure that stores a fixed-size sequence of elements of the same type. You can loop around an array to access and process each element individually.
// Looping around an array
int[] numbers = {1, 2, 3, 4, 5};
for (int number : numbers) {
System.out.println(number);
}
Output:
1 2 3 4 5
In this Java example, we define an array numbers
and use a "for-each" loop to iterate over each element in the array. The number
variable takes on the value of each element in the array, and we print it using System.out.println()
.
Now let's move on to looping around a list.
How to Declare & Initialize Array and List ?
Ans: Refer to the post Here for Details
Looping around a list:
A list is a dynamic data structure that can hold an ordered collection of elements. In Java, the java.util.List
interface is commonly used. Here's an example of looping around a list in Java:
import java.util.ArrayList;
import java.util.List;
// Looping around a list
List<String> names = new ArrayList<>();
names.add("John");
names.add("Alice");
names.add("Bob");
for (String name : names) {
System.out.println(name);
}
Output:
John Alice Bob
In this example, we create a list called names
and use the add()
method to add elements to the list. Then, we use a "for-each" loop to iterate over each element in the list and print it.
How to add/join/combine two ArrayList ?
: Refer to the link HERE for answers with the code.
Looping around the map:
A map is a data structure that stores key-value pairs. In Java, the java.util.Map
interface is commonly used. Here's an example of looping around a map in Java:
import java.util.HashMap;
import java.util.Map;
// Looping around a map
Map<String, Integer> ages = new HashMap<>();
ages.put("John", 25);
ages.put("Alice", 30);
ages.put("Bob", 35);
for (Map.Entry<String, Integer> entry : ages.entrySet()) {
String name = entry.getKey();
int age = entry.getValue();
System.out.println(name + ": " + age);
}
Output:
makefile
John: 25
Alice: 30
Bob: 35
In this example, we create a map called ages
and use the put()
method to add key-value pairs to the map. Then, we use a "for-each" loop with entrySet()
to iterate over each key-value pair in the map. We extract the key and value using the getKey()
and getValue()
methods, respectively, and print them.
How to Sort a Hashmap in Java?
I hope this helps you understand how to loop around arrays, lists, and maps in Java!
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