Chapter 2

Question 1

What is the difference between a string literal and a literal

Answer 1

A string literal is presented by putting double quotes around the text. A liteal is an explicit data value used in a program.

Question 2

What is the string concatenation?

Answer 2

The string concatenation operator (+) concatenates / puts together different string together.
For example, “Peanut butter” + “and jelly”.

Question 3

Why is the following statement wrong?System.out.println(“We present the following facts
for your extracurricular edification:”);

Answer 3

The System.out.println cannot be divided into two different lines. If we want to distribute the code onto two different lines, we will have to write two times the method.

Question 4

When concatenating in a println method, what’s the difference between writing: + 34 + 35 and + (34 + 35) ?

Answer 4

Without parenthesis 34 and 35 get only concatenated, for them to be added and then displayed we will have to use the parenthesis.

Question 5

What are escape sequences?

Answer 5

Escape sequences are a particular form of writing that allows particular characters written in a string not to be confused with synctactical parts of the programming language.

If you were to write …(“John:”I’m coming””);
Java would not understand which quotas are the extremes of a string and which are intended as a character.

So we write:
\" for commas.
\n new line
\t tab
\' quote
\\ backslash

Question 6

What is a variable?

Answer 6

A variable is a name for a location in memory that holds a value.

Question 7

How do you declare a variable?

Answer 7

You define the data type (like int, double, char, etc), you write the desired name of the variable and you CAN (not necessary) write the variable’s value.

Question 8

How do you declare a constant? What is its use in Java?

Answer 8

A constant is defined in the same way as a variable, but at the beginning there must be written “final”. The variable should follow the convention and be written with capital letters only.
Constants are used to distinguish specific variables from others, to avoid writing various variables with the same value and to avoid their values be changed by error.

Question 9

What are the eight primitive data types in Java?

Answer 9

Integers: byte, short, int, long
Floating point numbers: float, double
Characters: char
Boolean values: boolean

Question 10

What is the max value of each of these data types?

byte, short, int, long

Answer 10

byte = 127
short = 32 767
int = 2 147 483 647
long = > 9 * 10^18

Question 11

What does a char variable store?

Answer 11

A char variable stores a single character. Those are delimited by single quotes: ‘a’, ‘X’, ‘7’, ‘,’, ‘\n’.

Question 12

What is the difference between a char variable and a string?

Answer 12

A char variable contains only one character, while a string contains a series of characters.

Question 13

What is a character set?

How many bits used Unicode?

Answer 13

It is an ordered list of characters, with each character corresponding to a unique number.
Unicode uses sixteen bits to store characters, allowing to 65 536 differenct characters.

Question 14

What is the ASCII character set?

Answer 14

It is an older and smaller character set, but it’s still quite popular.

Question 15

How do you assign characters?

Answer 15

char c = ‘\u005B’; -> you assign the character with that unicode value.
char d = 91; -> you assign the character with that unicode value, but written in decimal form.

Question 16

What is a boolean variable?

Answer 16

A boolean variable contains either the true or the false condition.

Question 17

What is an expression?

Answer 17

An expression is a combination of one or more operators and operands that produces a result.

Question 18

What's the difference between the following writings?
14.0 / 3.0 or 14.0 / 3
and
14 / 3
?

Answer 18

With any floating number (or variable), all members of the division and of the following arithmetic operations will be transformed into a floating number, leading to result written in a floating way.
In the other case, two integers dividing will produce an integer result, discarding any obtained remainder.

Question 19

In a long arithmetic expression, how does Java “think”? What is the order of any operation inside the arithmetic expression?

Answer 19

Java reads left to right. When encountering an operator between two objects, it will first check if any other more important operators adjacent to the objects are present, if not it will execute the operation, even if other more important operations are to be found inside the whole arithmetic expression. Brackets can help to secure and to understand better the order of operations that Java will have to execute.

Question 20

In what order are the operations in the following expression executed?
a + b * c - d / e

Answer 20

a + b * c - d / e

2 1 4 3

Question 21

What are the ++ and – operators? And what is the difference between a++ and ++a

Answer 21

The ++ and – operators are respectively called increment and decrement. Connected to a variable they increment or decrement its value of 1.
Writing a++ means that Java will consider the value a first and will then add 1. Writing ++a means Java will take 1 first and then add it to a. This difference is useful when writing particular arithmetic expressions, as it can change the result.

Question 22

What does num += count mean? And other situations with num ?= count ?

Answer 22

num += count -> num = num + count.
num -= count -> num = num -count
num *= count -> num = num * count
and so on

Question 23

What is the difference between widening and narrowing data conversions? What are the three possibile data conversions?

Answer 23

When converting data from one type to another, some conversions can be subject to data loss: these are called narrowing conversions. Conversions that are not subject to data loss are called widening.

• Assignment conversion:
  only widening. It happens when the assignment of a variable is equal to the variable of a lower data type (in the sense that the new variable has more “space” to store the value of the assigned variable, hence not losing any data)
• Promotion:
  only widening. It happens when two variables of two different data type are put together in an arithmetic operation. All variables are taken to the same level, without loss of data.
• Casting:
  Casting is a special case in which narrowing conversions are also possible. Normally, Java would signal an error everytime a narrowing operation will be displayed. If you put the desired data type inside brackets, Java will ignore the problem and narrow the data in the best possible way, although data loss is to be expected.
  Ex:
  int total = 50;
  float result = (float) total / 6.

Question 24

What does the following mean?
Scanner scan = new Scanner(System.in)

Answer 24

Scanner is an object created by the class Scanner.
scan is the variable created from the scanning.
new is the method that creates the new object Scanner.
Scanner(System.in) indicates from where the scan should be taken, in this case the keyboard.

Question 25

What does the “next” method of the Scanner class do?

Answer 25

When accompanied with nextInt or nextDouble it reads the next input on the keyboard and saves it as variable int or double (like in this example)

Question 26

What are the four types of variables in Java?

Answer 26

1. Instance Variables (Non-Static Fields):
   In each object, any variable can have such variables, as they’re unique to each instance of a class.
2. Class variables (Static Fields):
   These type of variables indicate the identifier that there’s only one instance of this variable in existance. So the number of times in which an object would have been instantieted will be irrelevant.
3. Local variables:
   Local variables are temporarily created and are used by the methods during its execution.
4. Parameters:
   A parameter acts as a variable inside the method to transmit a variable from outside the method.