Java

Question 1

what is JDK?

Answer 1

Java Development Kit and it’s used to create and run java programs

Question 2

Main Method?

Answer 2

It is the entry point of any java program and like any other method it has a number of statements that execute a number of operations

Question 3

Can reserved keywords used in any order?

Answer 3

no reserved keywords must be used in a specific order like public static void can’t be public void static

Question 4

Statement

Answer 4

is a complete command to be executed and can contain one or more expressions

Question 5

Variables

Answer 5

are a way to store our information in Ram

Question 6

Declaration Statement

Answer 6

used to define a variable by giving it a datatype and a name and optionally an expression to set the initial value

Question 7

how many data types are in java and what are they?

Answer 7

they r eight … int , float , double ,short , long , char , boolean , byte

Question 8

Wrapper class

Answer 8

there is a wrapper class for each primitive type to be able to deal with the primitive types like methods and such

Question 9

what are overflow and underflow?

Answer 9

is to exceed to maximum number or minimum number which in turn just skips to the opposite direction

Question 10

how many bits does byte , short , int , long occupy in memory?

Answer 10

8 , 16 , 32 , 64

Question 11

Casting

Answer 11

is the process of converting on type to another using (type)

Question 12

which occupies more memory and has more percision float or double?

Answer 12

double has 64 bit and more precise while float has 32 bit

Question 13

should we use float or double for precise calculations?

Answer 13

No. we should use BigDecimal class due to limitations of how float and double are stored in memory and that’s not a java problem

Question 14

is Char type 1 byte or 2 bytes

Answer 14

it’s 2 bytes because it allows unicode to be stored meaning it’s 16 bit

Question 15

Unicode

Answer 15

it’s an international encoding standard to represent characters or digits or symbols as unique numerics

Question 16

what is a string?

Answer 16

a string is an immutable class of characters back to back which means it’s can’t be changed instead it is created again and the variable is assigned the new value and using this method is actually inefficient and better use StringBuffer

Question 17

Operator

Answer 17

is a special symbol that performs an operation on two or more operands

Question 18

Conditional logic

Answer 18

allow us to check to check for a condition and based on the result a certain piece of code is executed

Question 19

Method OverLoading

Answer 19

it’s a feature that allows us to use the same name of method but different parameters meaning different implementations

Question 20

an example of built in java overloading?

Answer 20

println

Question 21

benefits of overloading

Answer 21

increase readability and re-usability and it’s easier to remember one method and achieves consistency in naming and flexibility

Question 22

how to parse string

Answer 22

using wrapper.Parseprimitivetype

like Integer.parseint()

Question 23

how to read user input?

Answer 23

by using the scanner class
Scanner scanner = new Scanner(System.in)
scanner.nextline()
scanner.nextint()

Question 24

do u have to create the constructor manually?

Answer 24

No java has a default constructor

Question 25

how many times a constructor is called?

Answer 25

only once at the intialization of the object

Question 26

can u overload constructors?

Answer 26

yes

Question 27

can u call a constructor inside of another construcotr

Answer 27

yes by using this()

Question 28

what is the only rule to call a constructor inside of another constructor?

Answer 28

the call must be in the first line

Question 29

what is mandatory when u create a class that extends another class?

Answer 29

u must create a default constructor to call the parent constructor

Question 30

what is super keyword?

Answer 30

it deals with methods and field of parent class

Question 31

what is a class?

Answer 31

it's the blueprint to make objects from

Question 32

what is an object or an instance?

Answer 32

it's an instance of a class

Question 33

what is a reference

Answer 33

it's the variable holding the address pointing to that object in memory

Question 34

what happens when u change something on one reference?

Answer 34

it changes the other as both of them point to the same physical entity

Question 35

what is derefrencing?

Answer 35

it's making one reference point to another object

Question 36

is there anyway to access the object directly?

Answer 36

no u must have a reference

Question 37

what is a common way to call super

Answer 37

when overriding a method in a parent class

Question 38

what is this keyword

Answer 38

it's user to reference methods or variables in the same class

Question 39

this() vs super()

Answer 39

this or super calls the constructor and it must be the first statement and they can only be used in a constructor

Question 40

can u call this() and super() at the same time?

Answer 40

No

Question 41

is overloading related to polymorphism?

Answer 41

No, but some developers like to call it compile time polymorphism because at compile time the compiler decided what method to call based and it's name , return type , parameter list

Question 42

can u overload a static method?

Answer 42

yes as well as instance methods

Question 43

can u overload in a subclass?

Answer 43

yes by having a different name

Question 44

what are the rules for method overloading?

Answer 44

1 - must have the same name 2- different argument list they may or may not have the following 1 - same return type 2 - throw an exception 3 - have different access modifiers

Question 45

what is a method overriding?

Answer 45

it's defining a method with the same name and arguments (same signature) that already exists in the parent class

Question 46

what the the overriding polymorphism called?

Answer 46

RunTime polymorphism or run time dispatch because the method that is getting called is decided at run time by the JVM

Question 47

what is @Override

Answer 47

it's an annotation that tells the compiler that we are overriding a method and it will show an error if we don't override correctly

Question 48

can we override a static method?

Answer 48

No we can only override an instance method

Question 49

what are the rules for method overriding?

Answer 49

``` 1 - they must have the same name and arguments 2- the return type can be a subclass of the parent 3 - the access modifier can't be a lower visibility of the parent class ```

Question 50

what are the methods that can't be overriden?

Answer 50

constructors , private , final

Question 51

can overriden method throw a broader exception or different one?

Answer 51

no

Question 52

what is a covariant return type?

Answer 52

when a class extends another class they are called covariants

Question 53

what is a static method?

Answer 53

it's a method that can't be called with "this" which points to an instance of that method and it can't access any instance method or instance variable

Question 54

how do u call a static method?

Answer 54

with the class name

Question 55

how to access an instance method?

Answer 55

u must have an instance of the class and they can access static and instance methods and variables

Question 56

static or instance method?

Answer 56

if u use any instance variable? then use instance else use static

Question 57

what is a static variable?

Answer 57

it's a variable shared among all the instances of that class so if that variable changes then all other instances change

Question 58

an example to use a static variable?

Answer 58

scanner

Question 59

what is an instance variable?

Answer 59

every instance of a class has a copy of that variable

Question 60

what is encapsulation?

Answer 60

it's protecting the inner workings of a class from outside behavior

Question 61

what is the type of primitive?

Answer 61

value types meaning they are copied where each variable works independently

Question 62

what is the type of an object or an array

Answer 62

reference type which means that the address get stored both pointing to the same object