Java Identifiers, Primitivies, & Reference Types

Question 1

Legal Java identifies can only being with the following characters:

Answer 1

A letter
The $ character
The _ character

Question 2

Can numbers be used in Java identifiers?

Answer 2

Yes but it can’t be the first character in the variable name.

Question 3

If a Java identifier is composed only of letters, is it always a legal variable name?

Answer 3

No. Java reserved words can not be used as variable names.

Question 4

With the exception of the first character, legal Java identifies can only contain the following characters:

Answer 4

Letters
Numbers
The $ character
The _ character

Question 5

What structures in Java are named using identifiers?

Answer 5

Variables
Methods
Classes
Fields

Question 6

What is a variable?

Answer 6

A variable is a name for a piece of memory that stores

data.

Question 7

What are the minimum requirements when declaring a variable in Java?

Answer 7

At a minimum, a variable must have a variable type and an identifier (or name).

Question 8

Java has two types of data variables, what are they?

Answer 8

Primitive Types

Reference Types

Question 9

How many primitive types (or primitives) does Java have?

Answer 9

8

Question 10

What are the Java primitive types?

Answer 10

boolean
byte
short
int
long
float
double
char

Question 11

How much memory is required for a byte? What values can it hold? What is its default value?

Answer 11

8-bits or 1 byte
-128 to 127
0

Question 12

How much memory is required for a short?What values can it hold?What is its default value?

Answer 12

16-bits or 2 bytes
-32,768 to 32,767
0

Question 13

How much memory is required for an int? What values can it hold? What is its default value?

Answer 13

32-bits or 4 bytes
-2^31 to (2^31)-1
0

Question 14

How much memory is required for a long? What values can it hold? What is its default value?

Answer 14

64-bits or 8 bytes
-2^63 and a maximum value of (2^63)-1
0L

Question 15

How much memory is required for a float?

Answer 15

32-bits or 4 bytes

Question 16

How much memory is required for a double?

Answer 16

64-bits or 8 bytes

Question 17

How much memory is required for a char in Java 8? What values can it hold? What is its default value?

Answer 17

16-bits or 2 bytes
A Unicode character
‘\u0000’

Question 18

What is the default value of a boolean?

Answer 18

false

Question 19

Does the following line of code compile?
long max = 3123456789;
Why or why not?

Answer 19

No. When using literal values, Java treats numbers like ints. This value is greater than the maximum int value. To fix the problem append ‘L’ to make Java treat this is a long.

long max = 3123456789L;

Question 20

How do you specify that a literal is an octal value?

Answer 20

Prefix the number with a 0 and only use characters 1 - 7.

Example: 017

Question 21

How do you specify that a literal is a hexadecimal value?

Answer 21

Prefix the number with a 0x or 0X followed by the values 0 - 9 and/or A - F.
Example: 0xA4

Question 22

How do you specific that a literal is a binary value?

Answer 22

Prefix the number with a 0b or 0B followed by the values 0 - 1.
Example: 0b10110101

Question 23

Does the following code compile in Java 8?

int million = 1_000_000;

Why or why not?

Answer 23

Yes. As of Java 7, there was a feature added to numeric literals allowing you to add underscores to the number to make them easier to read.

You can add underscores anywhere except at the beginning of a literal, the end of a literal, right before a decimal point, or right after a decimal point.

Question 24

Does the following code compile in Java 8?int million = _1000000;Why or why not?

Answer 24

No. As of Java 7, there was a feature added to numeric literals allowing you to add underscores to the number to make them easier to read.

You can add underscores anywhere except at the beginning of a literal, the end of a literal, right before a decimal point, or right after a decimal point. This has an underscore at the beginning.

Question 25

Does the following code compile in Java 8?int million = 1_00_0.0_0;Why or why not?

Answer 25

Yes. As of Java 7, there was a feature added to numeric literals allowing you to add underscores to the number to make them easier to read.This doesn’t actually make the number easier to read but it is legal.

Question 26

What is a literal?

Answer 26

A Java literal is a syntactic representation of Boolean, character, numeric, or string data.

Question 27

How do you represent boolean literals?

Answer 27

With the keywords true or false.

Question 28

When using a numeric literal if there are no other qualifiers, what type does it default to?

Answer 28

An int.

Question 29

Can you assign a long literal to an int if the long value is less than the maximum size of an int?

Answer 29

No.

Question 30

Can you assign a binary literal value to an int if the binary value is less than the maximum size of an int?

Answer 30

Yes. This is also true of hexadecimal and octal values.

Question 31

What is appended to a numerical literal to denote that it is a long?

Answer 31

An L. You can use either the upper or lowercase L, however the uppercase L is recommended as the lowercase L looks like the number 1 in some fonts.

Question 32

What does a reference type refer to?

Answer 32

An object.

Question 33

Do reference types refer to primitives?

Answer 33

Not directly. A reference type always points to an object. However, the object could be nothing but a wrapper for a primitive.

Question 34

What are the 2 ways are values assigned to a reference?

Answer 34

A reference can be made to point to an existing object of the same type.

A reference can be made to point to a new object using the new keyword.

Question 35

Can a reference be assigned a value of null?

Answer 35

Yes.

Question 36

Can a primitive be assigned a value of null?

Answer 36

No.

Question 37

Can a reference be used to call a method?

Answer 37

Yes.

Question 38

Can a primitive be used to call a method?

Answer 38

No.

Question 39

How do you declare multiple variables on a single line?

Answer 39

There are two ways. Example:
int a; int b; int c;
OR
int a, b, c;

Question 40

How do you initialize multiple variables on a single line?

Answer 40

There are two ways. Example:
int a = 1; int b = 2; int c = 3;
OR
int a = 1, b = 2, c = 3;

Question 41

Can you declare variables of different types on the same line without a semicolon?

Answer 41

No. The following is an error:
int a, String b;
However:
int a; String b;
is acceptable.

Question 42

When using only a comma to declare multiple variables, how many variable type keywords can you use (between semicolons)?

Answer 42

Only 1. Example:
OK: double d1, d2, d3;
BAD: double d1, double d2;

Question 43

What is a local variable?

Answer 43

A local variable is a variable defined within a method.

Question 44

Do local variables have a default value?

Answer 44

No. They have garbage data in them. Code with local variables will not compile if the variable is used before being initialized.

Question 45

What is an instance variable?

Answer 45

An instance variable is any variable declared outside a method that is not declared static. They are so named because they are unique to their instance of the object.

Question 46

What is a class variable?

Answer 46

A class variable is any variable declared static and outside a method. They are so named because their is only one for all the objects made from the class.

Question 47

Which variables do not need to be initialized?

Answer 47

instance and class variables.

Question 48

What is the scope of a variable?

Answer 48

Scope is where in the code a variable can be accessed.

Question 49

How do you determine the scope of a variable?

Answer 49

A variable is not directly accessible outside the code block in which it was declared. However, as in the case of the class variable, it may be accessible across multiple objects.

Stated another way:
Local Variables: in scope from declaration to end of block

Instance Variables: in scope from declaration until object garbage collected

Class Variables: in scope from declaration until program ends.