Arrays, Java inbuilt Lists, Autoboxing and Unboxing

Question 1

Array

Answer 1

• a data structure that allows you to store multiple values of the same type into a single variable
• the default values of numeric array elements are set to zero
• arrays are zero-indexed

Question 2

Explain code:

int [ ] reference = new int [number]

Answer 2

• new keyword is used to create the array and initialize the array elements to their default values

Question 3

Explain code:

scanner. nextInt();
scanner. nextLine();

Answer 3

when you have the nextInt() method, it only consumes the number and leaves the "enter" behind (in the buffer). 
The nextLine() method will clear that "enter" from the buffer first.

Question 4

ArrayIndexOutOfBoundsException

Answer 4

xxx

Question 5

[ ]

Answer 5

square brackets [ ] would indicate an array

Question 6

{ }

Answer 6

• code block

- array initializer block

Question 7

Reference type vs Value type

Answer 7

• the primitive data types are predefined
• the reference data type refers to where data is stored. They contain the reference/addresses of dynamically created objects.
• once we create a reference variable, they only store the address of these values.

Question 8

Write the general syntax to create and declare an ArrayList object

Answer 8

ArrayList < type > reference = new ArrayList<> ();

• the type can be primitive like int, double, boolean
• it also can be String, the objects you create

Question 9

ArrayList

Answer 9

• the ArrayList class is a resizable array.

- it can be found in java.util package

Question 10

Write the general syntax to declare, declare and instantiate, declare and instantiate and initialize an array

Answer 10

type [ ] reference;
type [ ] reference = new type [size];
type [ ] reference = new type [size] {array literal}

Question 11

autoboxing

Answer 11

automatic conversion of primitive types to the object of their corresponding wrapper class

Question 12

unboxing

Answer 12

• the reverse process of autoboxing

- automatically converting an object of a wrapper class to its corresponding primitive type

Question 13

LinkedList

Answer 13

• a linear data structure that contains a sequence of nodes, in which each node contains data and a pointer (reference) to another node.
• singly linked list and doubly linked list
• to access our desired value, we would have to traverse the linked list and continue accessing the next value of each node until arriving at it

Question 14

Write the syntax of enhanced for loop in Java?

Answer 14

for (declaration: expression) {
    // statements
}

Question 15

How to create an ArrayList instance?

Answer 15

ArrayList < type > reference = new ArrayList < >;

Question 16

Compare ArrayList and LinkedList

Answer 16

ArrayList class

• it uses a dynamic array to store the elements
• it supports the storage of all types of objects
• manipulating ArrayList takes more time due to shifting the memory bits
• it implements a List interface so it acts as a list
• it works better when the application demands storing the data and accessing it

LinkedList class

• it uses a doubly linked list to store the elements.
• it supports the storage of all types of objects.
• manipulating LinkedList takes less time compared to ArrayList because there is no shifting memory bits. The list is traversed and the reference link is changed
• it implements both the List interface and the Deque interface so it acts as a list and a deque
• it works better when the application demands manipulation of the stored data