Java Fundamentals

Question 1

Type float has _ bits and double type has _ bits

Answer 1

Type float has 32 bits and double type has 64 bits

Question 2

What does a cast do

Answer 2

Performs an explicit conversion between incompatible data types

Question 3

What does it mean java is a strongly typed language

Answer 3

it means that the compiler checks all operations for type errors, eg. variables have to adhere to their defined data types

Question 4

What does static do?

Answer 4

Static allows a member of a class to be used independently of any object of that class

Question 5

What is a bytecode?

Answer 5

A set of instructions designed to be interpreted by a java virtual machine. Bytecode results from java source code compilation by the java compiler

Question 6

What is a default constructor

Answer 6

A default constructor is a constructor that takes no arguments

Question 7

What is boxing

Answer 7

Boxing is the process of encapsulating a value within an object

Question 8

What is the function of a constructor?

Answer 8

A constructor initializes an object immediately upon creation:

Books myBook = new Books() //object myBook is initialized by the Books constructor

Question 9

what is this keyword used for

Answer 9

the this keyword is used in a non-static method to refer to the object that invoked the method

Question 10

What is unboxing

Answer 10

Unboxing is the process of extracting a value from a type wrapper

Question 11

Why is java considered portable

Answer 11

Its considered portable because of the java bytecode that can run on a jvm, which in turn runs on different platforms

Question 12

Why is java considered secure

Answer 12

Java is considered secure because java programs are constrained within the jvm, preventing them from generating harmful side effects that run outside of the jvm

Question 13

What are the 8 primitive java data types

Answer 13

boolean, short, int, float, double, char, byte,long

Question 14

What are the restrictions faced by methods declared as static?

Answer 14

1. They can only call other static methods
2. They must access only static data
3. They cannot refer to this or super

Question 15

What are wrappers

Answer 15

Wrappers are classes that encapsulate a primitive type within an object

Question 16

What is a bytecode?

Answer 16

A set of instructions designed to be interpreted by a java virtual machine. Bytecode results from java source code compilation by the java compiler

Question 17

Why is java considered portable

Answer 17

Its considered portable because of the java bytecode that can run on a jvm, which in turn runs on different platforms

Question 18

A string instance variable has a default initial value of _

Answer 18

A string instance variable has a default initial value of NULL

Question 19

An integer instance variable has a default initial value of _

Answer 19

An integer instance variable has a default initial value of 0

Question 20

By default, floating-point literals are of type _

Answer 20

By default, floating-point literals are of type double

Question 21

By default, integer literals are of type _

Answer 21

By default, integer literals are of type int

Question 22

Characters in java are indices into the _ character set, and they are _ bit values that can be converted into_ and manipulated with _ operators, such as _ and _ operators

Answer 22

Characters in java are indices into the Unicode character set, and they are 16-bit values that can be converted into integers and manipulated integer operators, such as the addition and subtraction operators

Question 23

Describe \

Answer 23

Backslash

Question 24

Describe \b

Answer 24

Backspace

Question 25

Describe a decimal number system

Answer 25

A decimal number system is based on 10, it goes from 0 to 9

Question 26

Describe a hexadecimal number system

Answer 26

A hexadecimal is a number system that is based on 16. i.e. it goes from 0 to 9 and then from A to F, with the letters representing 10, 11, 12, 13, 14, 15

Question 27

Describe a java applet

Answer 27

A java applet is a small dynamic java application that runs on the web, performing tasks such as interactive animation, calculations and other simple tasks without having to send a user request back to the server

Question 28

Describe a literal

Answer 28

A literal is fixed value that is represented in human-readable form

Question 29

Describe advantages of encapsulation

Answer 29

1. Protects encapsulated data | 2. Changes are restricted to the objects or classes

Question 30

Describe an instance variable

Answer 30

A variable within a class defined outside of a method, which is available to any instance of the class to which it (instance variable) belongs to

Question 31

Describe an octal number system

Answer 31

An octal is a number system that is based on 8 i.e. the numbers go from 0 to 7

Question 32

Describe auto-unboxing

Answer 32

Auto-unboxing is the process by java automatically extracts a value from a type wrapper when its value is needed

Question 33

Describe autoboxing

Answer 33

autoboxing is the process whereby java automatically encapsulates a primitive type into its equivalent wrapper whenever an object of that type is required

Question 34

Describe encapsulation

Answer 34

In its simplest form, encapsulation is information hiding. It is a concept whereby data and the code that works on the data are combined to form an object, and are hidden from external parts

Question 35

Describe Inheritance

Answer 35

The process by which an object can inherit the properties of another object

Question 36

Describe Polymorphism

Answer 36

Polymorphism is a concept that allows a general interface to make use of a general class - one interface taking multiple forms

Question 37

Describe the advantage(s) of auto-unboxing

Answer 37

Auto-unboxing always creates the right value

Question 38

Describe the advantage(s) of autoboxing

Answer 38

Autoboxing always creates the proper object, ie compatible types are created

Question 39

Describe the three select statements available in java

Answer 39

1. if - single select statement, selects or ignores a single action 2. if...else - double select statement, selects between two actions 3. case - multiple select statement, selects among many different actions

Question 40

Explain Object Oriented Programming

Answer 40

Object Oriented Programming is a programming style that represents ideas as objects that contain data fields(attributes that describe the object) as well as procedures(methods) that operate on the objects. Example a human is an object, whose attribute is age, and has an associated procedure, speak, that the human can do.

Question 41

Floating-point types can represent numbers that have _ components

Answer 41

Floating-point types can represent numbers that have fractional components

Question 42

Give an example of auto-unboxing

Answer 42

Integer intBox = 3; //autoboxing | int i = intBox; //auto-unboxing

Question 43

Give an example of autoboxing

Answer 43

Integer intBox = 3; //autoboxing

Question 44

Give an example of boxing

Answer 44

Integer boxInt = new Integer(100)

Question 45

Give an example of unboxing

Answer 45

``` Integer boxInt = new Integer(100) //boxing int unboxInt = boxInt.intValue() //unboxing ```

Question 46

How do you call a static method from outside its class

Answer 46

classname.method()

Question 47

How do you define an array when you do not know the size of the array?

Answer 47

``` You use the new keyword, e.g. int [] a; Random rand = new Random(); a = new int [rand.nextInt()]; ```

Question 48

How do you specify a float literal?

Answer 48

By appending an f or F in front of the literal, eg. 5.2f

Question 49

How do you specify a long literal?

Answer 49

By appending an L or l in front of the literal, eg. 5L

Question 50

How does the switch statement work

Answer 50

performs one of many different actions, depending on the value of the expression

Question 51

In Java, char is an _ 16-bit type

Answer 51

In Java, char is an unsigned 16-bit type

Question 52

Java does not support unsigned integers. What are unsigned integers?

Answer 52

Unsigned integers are integers that only support positive integers

Question 53

Java supports signed integers. What are signed integers

Answer 53

Signed integers are integers that support both positive and negative integers

Question 54

Java Virtual Machine

Answer 54

a JVM is part of the java runtime architecture that is responsible for the interpretation of the java bytecode

Question 55

public static void main(String args[]){} | explain main

Answer 55

main is the class from which all java applications execute

Question 56

public static void main(String args[]){} what does static do

Answer 56

Static allows main to be called before an object of the class has be created

Question 57

The smallest type of an integer is called _

Answer 57

the smallest type of an integer is a byte

Question 58

True or False, the order of initialization follows the order in which the variables are defined within a class

Answer 58

True

Question 59

True or False, variables declared inside a method are initialized by java

Answer 59

False - variables declared inside a method are not initialized by java

Question 60

True or False, you cannot apply the static keyword to local variables, it only applies to fields (instance variables)

Answer 60

True