Variables and Primitive Data Types

Question 1

Variable

Answer 1

A variable or scalar is a storage location (identified by a memory address) paired with an associated symbolic name (an identifier), which contains some known or unknown quantity of information referred to as a value.

Question 2

Data Type

Answer 2

A data type or simply type is a classification of data which tells the compiler or interpreter how the programmer intends to use the data. Most programming languages support various types of data, for example: real, integer or Boolean.

Question 3

Assignment Operator

Answer 3

One of the most common operators that you’ll encounter is the simple assignment operator “ = “. it assigns the value on its right to the operand on its left: …

Question 4

Value Assignment

Answer 4

Storing data in the variable

Question 5

Primitives

Answer 5

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

Question 6

byte

Answer 6

The byte data type is an 8-bit signed two’s complement integer. It has a minimum value of -128 and a maximum value of 127 (inclusive). The byte data type can be useful for saving memory in large arrays, where the memory savings actually matters. They can also be used in place of int where their limits help to clarify your code; the fact that a variable’s range is limited can serve as a form of documentation.

Question 7

short

Answer 7

The short data type is a 16-bit signed two’s complement integer. It has a minimum value of -32,768 and a maximum value of 32,767 (inclusive). As with byte, the same guidelines apply: you can use a short to save memory in large arrays, in situations where the memory savings actually matters.

Question 8

int

Answer 8

By default, the int data type is a 32-bit signed two’s complement integer, which has a minimum value of -231 and a maximum value of 231-1. In Java SE 8 and later, you can use the int data type to represent an unsigned 32-bit integer, which has a minimum value of 0 and a maximum value of 232-1.

Ex:
int myAge;
myAge = 45;

Question 9

long

Answer 9

The long data type is a 64-bit two’s complement integer. The signed long has a minimum value of -263 and a maximum value of 263-1. In Java SE 8 and later, you can use the long data type to represent an unsigned 64-bit long, which has a minimum value of 0 and a maximum value of 264-1. It needs to end with letter “L” at the end.

Question 10

float

Answer 10

The float data type is a single-precision 32-bit IEEE 754 floating point. Its range of values is beyond the scope of this discussion, but is specified in the Floating-Point Types, Formats, and Values section of the Java Language Specification. As with the recommendations for byte and short, use a float (instead of double) if you need to save memory in large arrays of floating point numbers. It needs to end with letter “f” at the end.

Question 11

double

Answer 11

The double data type is a double-precision 64-bit IEEE 754 floating point. For decimal values, this data type is generally the default choice.

Ex:
double d = 45.1;

Question 12

boolean

Answer 12

The boolean data type has only two possible values: true and false. Use this data type for simple flags that track true/false conditions.

Ex:
boolean isDoorOpen;
isDoorOpen = true;
System.out.println(isDoorOpen);

Question 13

char

Answer 13

The char data type is a single 16-bit Unicode character.

Ex:
char gChar = ‘g’

Question 14

String

Answer 14

Most common used data type. String is a sequence of characters, surrounded by double quotes (“”). It is not a primitive.

Question 15

concatenation

Answer 15

It is the operation of joining character strings end-to-end.

Question 16

”+”

Answer 16

Addition
Example: 34 +1
Result: 35

Question 17

”-“

Answer 17

Subtraction
Example: 34.0 - 0.1
Result: 33.9

Question 18

“*”

Answer 18

Multiplication
Example: 300 * 30
Result: 9000

Question 19

”/”

Answer 19

Division
Example: 1.0 / 2.0
Result: 0.5

Question 20

”%”

Answer 20

Remainder
Example: 20 % 3
Result: 2

Question 21

What are the rules for naming variables:

Answer 21

1. All variable names must begin with a letter of the alphabet, an underscore, or ( _ ), or a dollar sign ($). The convention is to always use a letter of the alphabet. The dollar sign and the underscore are discouraged.
2. After the first initial letter, variable names may also contain letters and the digits 0 to 9. No spaces or special characters are allowed.
3. The name can be of any length.
4. Uppercase characters are distinct from lowercase characters. Using ALL uppercase letters are primarily used to identify constant variables. Remember that variable names are case-sensitive.
5. You cannot use a java keyword (reserved word) for a variable name.

Question 22

int num = 10;

Explain each

Answer 22

int: is the type of the variable declared.
num: is the name of the variable.
= is the assignment operator. It tells to store the value 10 to the variable num