Language Basics: Variables: Primitive Data Types

Question 1

Is Java statically-typed?

Answer 1

Yes

Question 2

What does statically-typed mean?

Answer 2

All the variables must first be declared before they can be used. This involves stating the variables type and name.

Question 3

What is a primitive data type?

Answer 3

A primitive type is predefined by the language and is named by a reserved keyword. Primitive values do not share state with other primitive values.

Question 4

How many primitive data types does Java have?

Answer 4

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

Question 5

byte data type

Answer 5

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 6

short data type

Answer 6

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).

You can use a short to save memory in large arrays, in situations where the memory savings actually matters.

Question 7

int data type

Answer 7

By default, the int data type is a 32-bit signed two’s complement integer

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. Use the Integer class to use int data type as an unsigned integer.

Static methods like compareUnsigned, divideUnsigned etc have been added to the Integer class to support the arithmetic operations for unsigned integers.

Question 8

long data type

Answer 8

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.

Use this data type when you need a range of values wider than those provided by int.

The Long class also contains methods like compareUnsigned, divideUnsigned etc to support arithmetic operations for unsigned long.

Question 9

float data type

Answer 9

The float data type is a single-precision 32-bit IEEE 754 floating point.

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.

This data type should never be used for precise values, such as currency. For that, you will need to use the java.math.BigDecimal class instead. Numbers and Strings covers BigDecimal and other useful classes provided by the Java platform.

Question 10

double data type

Answer 10

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. As mentioned above, this data type should never be used for precise values, such as currency.

Question 11

boolean data type

Answer 11

The boolean data type has only two possible values: true and false.

Use this data type for simple flags that track true/false conditions. This data type represents one bit of information, but its “size” isn’t something that’s precisely defined.

Question 12

char data type

Answer 12

The char data type is a single 16-bit Unicode character. It has a minimum value of ‘\u0000’ (or 0) and a maximum value of ‘\uffff’ (or 65,535 inclusive).

Question 13

Is String a primitive data type?

Answer 13

No. But it is given special support in Java via the java.lang.String class.

Question 14

Are string objects immutable?

Answer 14

Yes, once a string object has been created, its value cannot be changed.

Question 15

What happens when you enclose a group of chars within double quotes?

Answer 15

A new String object is automatically created.

String s = “this is a string”;.

Question 16

Is it necessary to initialise variables?

Answer 16

Only local variables have to be initialised, not the other 3 variable types.

Local variables are slightly different; the compiler never assigns a default value to an uninitialised local variable. If you cannot initialise your local variable where it is declared, make sure to assign it a value before you attempt to use it. Accessing an uninitialised local variable will result in a compile-time error.

Question 17

What are the default values of variables when they are not initialised (apart from local variables which MUST be initialised)?

Answer 17

byte	       -            0
short      -            0
int	       -            0
long	       -            0L
float	       -            0.0f
double   -           0.0d
char	       -            '\u0000'
String (or any object) - 	null
boolean	        -             false

Question 18

Do primitive data types require ‘new’ keyboard?

Answer 18

No. Primitive types are special data types built into the language; they are not objects created from a class.

Question 19

What is a literal?

Answer 19

A literal is the source code representation of a fixed value; literals are represented directly in your code without requiring computation. As shown below, it’s possible to assign a literal to a variable of a primitive type:

boolean result = true;
char capitalC = 'C';
byte b = 100;
short s = 10000;
int i = 100000;

Question 20

integer long

Answer 20

An integer literal is of type long if it ends with the letter L or l; otherwise it is of type int. It is recommended that you use the upper case letter L because the lower case letter l is hard to distinguish from the digit 1.

Question 21

Hexadecimal values

Answer 21

Base 16, whose digits consist of the numbers 0 through 9 and the letters A through F
The prefix 0x indicates hexadecimal.

//  The number 26, in hexadecimal
int hexVal = 0x1a;

Question 22

Binary values

Answer 22

Base 2, whose digits consists of the numbers 0 and 1
The prefix 0b indicates binary.

// The number 26, in binary
int binVal = 0b11010;

Question 23

A floating-point literal is of type float if it ends with the letter F or f; otherwise its type is double and it can optionally end with the letter D or d.

The floating point types (float and double) can also be expressed using E or e (for scientific notation), F or f (32-bit float literal) and D or d (64-bit double literal; this is the default and by convention is omitted).

Answer 23

//all have same value
double d1 = 123.4;
double d2 = 1.234e2;
float f1  = 123.4f;

Question 24

Special escape sequences for char and String literals

Answer 24

\b (backspace), \t (tab), \n (line feed), \f (form feed), \r (carriage return), " (double quote), ' (single quote), and \ (backslash).

Question 25

null literal

Answer 25

Can be used as a value for any reference type. null may be assigned to any variable, except variables of primitive types. There’s little you can do with a null value beyond testing for its presence. Therefore, null is often used in programs as a marker to indicate that some object is unavailable.