Values and Data Types Flashcards
1
Q
What is a character set?
A
A character set is a defined list of characters recognized by a language
2
Q
What does a character set consist of?
A
- Alphabets: letters, A-Z, a-z
- Numerals: digits, 0-9
- Special characters: ?, %, }, >, @, etc.
3
Q
What are the alphabets and numerals collectively known as?
A
The alphanumeric character set
4
Q
Name two standard character sets
A
ASCII and Unicode
5
Q
What does ASCII stand for?
A
American Standard Code for Information Exchange
6
Q
What is ASCII?
A
It is a 7-bit set of codes that defines 128 different characters
7
Q
What is the ASCII character set enough to represent?
A
It is enough to represent every uppercase letter, lowercase letter, digit, and special character used in the English Language keyboard.
8
Q
What is Unicode?
A
It is an international character set designed to represent all the characters found in languages around the world, such as English, Hindi, Japanese, Chinese, French, Geman
9
Q
How many bits can Unidode use to represent a character?
A
8 to 32 bits
10
Q
Which character encoding does Java use?
A
The Unicode character coding
11
Q
How is a specific Unicode character expressed?
A
By using the escape sequence ā\uā followed by its four digit hexadecimal code
12
Q
What is the extended ASCII code?
A
It is an 8-bit character set that defines 256 different characters (2^8 = 256), including the standard 7-bit ASCII characters
13
Q
What are tokens?
A
Tokens are the smallest individual units of a Java program. All characters in a Java program are grouped into symbols called tokens.
14
Q
How many categories of tokens are in Java?
A
- Keywords
- Literals
- Operators
- Punctuators
- Identifiers
15
Q
What are keywords?
A
Keywords are the words that have a special meaning to the Java compiler
16
Q
What is another name for keywords?
A
Reserved words
17
Q
Why are keywords not available as names for variables or methods?
A
Java compiler reserves keywords for its own use, and hence they are not available
18
Q
Which keywords are currently not used in Java?
A
goto and const
19
Q
Name words you cannot use as variable names despite them not being keywords
A
true, false, null, literal values
20
Q
What are identifiers?
A
They are fundamental building blocks of a program & are used to name different components of a program, such as variables, methods, and objects
21
Q
What are the fundamental building blocks of a program?
A
Identifiers
22
Q
What are Java identifiers naming conventions?
A
- An identifier can consist of any combination of letters, digits, underscore character, dollar sign
- It cannot begin with a digit
- It may be of any length
- Both uppercase and lowercase letters can be used in naming an identifier
- Java is case sensitive, which means that two identifier names that differ only in uppercase and lowercase characters are considered to be different identifiers
- An identifier cannot be a keyword or a boolean literal or a null literal
23
Q
What are literals?
A
They are a sequence of characters that represent values in a program and are stored in variables. Literals are made out of digits, letters, and other characters
24
Q
Name the types of literals Java supports
A
- Numeric -> Integer and Real
- Non Numeric -> Character and String
- Boolean
- Null
25
What are numeric literals?
Values that may consist of digits (0-9), a decimal point (.), a positive (+) or negative (-) sign
26
Name the 2 types of numeric literals
Integer Literals
| Real Literals
27
What are integer literals?
Values that represent whole numbers only. They can be positive or negative values.
28
What is not allowed in integer literals?
Space, comma, and a decimal point not allowed
29
Give another name for real literals
Floating-point literals
30
What are real literals?
They represent values with a decimal point
31
Name the two ways in which real literals can be written
In fractional or exponential form
32
How is a real literal in the fractional form written?
It consists of signed or unsigned digits, including a decimal point between the digits. Eg. - +233.06
33
How is a real literal in the exponential form written?
It consists of two components: mantissa and exponent. Eg. -> 7.04*10^34 can be written as 7.04E34
34
What is the mantissa?
Component before E, in a real literal in exponential form
35
What is the exponent?
Component after E, in a real literal in exponential form
36
What would make a real literal invalid in exponential form?
1. No digit specified after E
2. The exponent is not an integer value
3. No digit before E
4. Comma
37
What would make a real literal invalid in fractional form?
1. No decimal point
2. No digit after the decimal point
3. No digit before the decimal point
4. Two decimal points
5. Comma
38
What are the two non-numeric literals?
Character literals
| String literals
39
What are character literals?
Literals of this type represent exactly one character enclosed in single quotes
40
What are Boolean Literals?
The logical values true and false are the boolean literals
41
What do true and false represent during logical evaluation?
On/off, yes/no, presence/absence of something
42
What is the null literal?
This is a special kind of literal which is represented by the keyword null or escape sequence '\0'
43
What are punctuators?
Symbols used for grouping and separating the code
44
Give another name for punctuators
Separators
45
Name some punctuators
; , {} () [] .
46
What is the use of semicolon?
Used to separate statements
47
What is the use of comma?
Used to separate consecutive identifiers in a variable declaration
48
What is the use of {}?
Used to define a block of code in a Java program. They are also used to initialize the values of arrays
49
What is the use of ()?
Parenthesis is used to define methods. They are also used to define the precedence of operators in an expression and conditions in control structures
50
What is the use of []?
Used to declare arrays and refer to values at a particular index
51
What is the use of .?
The period operator in Java is used to access member variables and methods. It is also used to differentiate the package names from sub-packages and class names
52
What are operators?
Operators are symbols that are used to perform arithmetic or logical operations in a given expression.
53
Name the main categories of operators in Java
1. Unary operators
2. Assignment Operator
3. Arithmetic Operators
4. Relational Operators
5. Increment/Decrement Operators
6. Logical Operators
7. Bitwise Operators
8. Conditional/Ternary Operators
54
What is an escape sequence?
It is a set of non-graphical characters that has a special meaning to the Java compiler.
55
What is the structure of an escape sequence?
In an escape sequence, a character is preceded by a backslash (\)
56
What does the usage of the backslash result in?
When you print a certain character, the same character is displayed on the screen, but when it is prefixed with '\', it is read as an escape sequence
57
What is the use of escape sequence '\n'?
Inserts a new line in the text at this point (shifts control to next line)
58
What is the use of escape sequence '\t'?
Inserts a tab in the text at this point
59
What is the use of escape sequence '\\'?
Inserts a backslash character in the text at this point
60
What is the use of escape sequence ' \" '?
Inserts a double quote character in the text at this point
61
What is the use of escape sequence ' \' "?
Inserts a single quote character in the text at this point
62
What is the use of escape sequence '\r'?
Inserts a carriage return in the text at this point (same as pressing the Enter key)
63
What is the use of escape sequence '\?'?
Inserts a question mark in the text at this point
64
What is the use of escape sequence '\a'?
Inserts an audible bell (beep sound)
65
What is the use of escape sequence '\0'?
Represents a null character
66
Name the two categories of data types
Primitive Data Types
| Non-Primitive Data Types
67
What are primitive data types?
The fundamental data types that are an integral part of the Java programming language
68
Give other names for primitive data types
Intrinsic or built-in data types
69
How many primitive data types are in Java?
1. byte
2. short
3. int
4. long
5. char
6. float
7. double
8. boolean
70
What are non-primitive data types?
The data types that are derived from primitive data types are called non-primitive.
71
Give other names for non-primitive data types
Reference types, composite data types, derived types
72
How many non-primitive data types are in Java?
Classes, arrays, interfaces
73
What are integer data types?
They are used to store whole numbers
74
Which four categories are integer data types divided into?
byte, short, int, long
75
What is the size of byte data type?
8 bits (1 byte)
76
What is the size of the short data type?
16 bits (2 bytes)
77
What is the size of the int data type?
32 bits (4 bytes)
78
What is the size of the long data type?
64 bits (8 bytes)
79
What is the range of byte data type?
-128 to 127 (-2^7 to 2^7 - 1)
80
What is the range of short data type?
-32,768 to 32,767 (-2^7 to 2^7 - 1)
81
What is the range of int data type?
-2 billion to +2 billion (approx.) (-2^31 to 2^31 - 1 )
82
What is the range of long data type?
-9E18 to +9E18 (approx.) (-2^63 to 2^63 - 1)
83
What can the floating-point data type be divided into?
Float and double data type
84
What is the size of the float data type?
32 bits (4 bytes)
85
What is the range of float data type?
1.4eā045 to 3.4e+038
86
What is the precision of the float data type?
Up to 7 significant decimal digits
87
What is the size of double data type?
64 bits (8 bytes)
88
What is the range of double data type?
4.9eā324 to 1.8e+308
89
What is the precision of double data type?
Up to 15 significant decimal digits
90
What does the float data type store?
Low precision digits, such as temperature, salary, and percentage
91
What does the double data type store?
High precision digits, such as scientific readings, the location of celestial bodies, and their distances.
92
What is the default data type of floating-point literal?
double
93
What do you need to do to designate a literal constant of the type float?
You must append the letter f or F. For eg., 6.7f or 6.7F
94
What is the size of the data type char?
16 bits (2 bytes)
95
What is the range of the data type char?
0-65535
96
Name a data type that supports the Unicode character set
char data type
97
What is the size of the boolean data type?
8 bits (1 byte) but uses only one bit
98
What is the range of the boolean data type?
true or false
99
Short description of boolean data type
Binary and boolean values
100
What is a variable?
It is an identifier that denotes a location in computer memory to store a data value. The variable may take different values at different times during the execution of the program
101
What is the condition for a variable to be used in a Java program?
It must be declared first
102
What does the computer do when it encounters a variable declaration?
1. Sets aside memory for the variable
| 2. Associates variable name with memory location
103
Give the syntax of a simple variable declaration
data-type variable-name;
104
What does variable initialization mean?
Assigning a value to the variable
105
What is the default value of byte data type?
0
106
What is the default value of short data type?
0
107
What is the default value of int data type?
0
108
What is the default value of long data type?
0L
109
What is considered to be a good programming practice in case of declaration?
Not depending on the default value of the declared variable and initializing it instead
110
What is the default value of float data type?
0.0f
111
What is the default value of double data type?
0.0d
112
What is the default value of char data type?
'\u0000'
113
What is the default value of boolean data type?
false
114
What is the default value of non-primitive type?
null
115
Which keyword is used to make the variable a constant?
final
116
What does the modifier final do?
In Java, the modifier final can be used in the variable declaration to ensure that the value stored in the variable cannot be changed after the variable has been initialized
117
What will the compiler show if an assignment operator tries to assign a value to a variable that has 'final' in front of it?
Syntax error
118
What are the advantages of using constants?
1. With an underscore, they improve the readability and understandability of the program
2. Any unintentional changes to such variables are flagged by the compiler
3. Later, if there is a change in the value of such a variable, you just need to modify its value at one place and all the occurrences will be taken care of automatically
119
_ do not change their value; _ can change their value
Constants, variables
120
What is the purpose of comments?
To document the code and provide additional information that is not readily available in it, so that even a layperson can understand the written code
121
Where can comments not appear?
In the middle of an identifier, a reserved word or a literal constant
122
Name the three styles of comments in Java
1. Single Line Comment
2. Multiline Comment
3. Documentation Comment
123
What is a single line comment?
It begins with a double slash (//) and continues to the end of the line
124
What does the compiler do if it encounters a double slash?
It ignores any text following it
125
What is a multiline comment?
It starts with initiating slash-asterisk (/*) and ends with terminating asterisk-slash (*/). There must be no space between the asterisk and the slash
126
What is a documentation comment?
It is a special comment that looks like a multiline comment, but it is generally used to generate external documentation about the source code
127
What does a documentation comment look like?
It starts with a forward slash followed by two asterisks (/**) and ends with an asterisk followed by a forward slash (*/)
128
What is documentation comment also called?
Javadoc
129
Name the points to remember while using comments
1. Keep your comments clear and concise
2. Arrange them in the code in an easy to see way
3. Don't make them too long or all over the statements
130
What are constants?
Memory locations whose values cannot be changed
131
Give another name for constants
Symbolic constants
132
The ASCII codes of A-Z are represented by decimal range?
65-90
