Chapter 2

Question 1

What is a constructor in java

Answer 1

this is a special type of method that creates a new object based on the parent Class.

Question 2

What is the correct syntax of a constructor within in a class

Answer 2

public name () {
}

Question 3

What does a normal method have that a constructor does not have

Answer 3

A return type

Question 4

What do we know of the name of a constructor class

Answer 4

The name matches the name of the parent class.

Question 5

what is between the braces in java { }

Answer 5

a Code block

Question 6

Name four types of code blocks

Answer 6

A Class definition
A Method declaration
A Inner Block
A instance initializer

Question 7

What is the correct order of initialization in a class in regards to running the code

Answer 7

Fields and instance initializer first in order of appearnce in the code (top to bot) Followed by the constructor.

Question 8

is a “String” variable a primitive type?

Answer 8

No, A string is a object, not a primitive type.

Question 9

What are correct values for a boolean

Answer 9

True or False

Question 10

What is the correct value range for a byte

Answer 10

-128 to 127

Question 11

what is the difference between a int and a float

Answer 11

The same range as the fields of a int, but with up to 7 decimal digits

Question 12

what is the difference between a long and a double

Answer 12

The same range as the fields of a long, but with up to 16 decimal digits

Question 13

what do all possible values of the ‘char’ type have in commen.

Answer 13

They are all members of the Unicode Ascii values

Question 14

What is a easy way to calculate the total range of a “byte”

Answer 14

A byte is 8 bits. A bit can have 2 values : 1 or 0. So a byte can have a range of 2^8 different combinations of bits.

Question 15

How are the maximum number of bits used by the Java engine.

Answer 15

Java uses the bits to figure out how much memeory is needed for a Var. For example Java allocates 32 bits if you write (int num;) Memory is wasted if the value of num never exceeds a “short” wich is halve the size.

Question 16

What happens when we you declare a value that fits a long and does not fit a int. But without including a capitol L at the end of the value.

Answer 16

java will throw a error because any number in java code is considered a int if not declared as a long by adding the L like : 3123456789L

Question 17

Where can you NOT use a underscore inside a number decleration.

Answer 17

Not at the start 001.0
Not at the end 001.0
Not next to a decimal. 001_.0

This is fine : 0_01.0 or 001_0

Question 18

will this compile :
String reference = “hello”
int len = reference.length();
int bad = len.length();

Answer 18

It will not compile.
len is a primitive data type that we can not use to call methods. The method length can be called on the string because a string is not a primitive.

Question 19

what is the difference between declaring a variable and initializing a variable.

Answer 19

A declared variable is not used yet, the java problem is simply aware of the variable and it can be initialized. Initializing the variable is the first time a value is assigned to this.

Question 20

What is the correct syntax to declare and initialize a variable

Answer 20

=
String zooName = “Arits”;
or
int numberAnimals = 100;

Question 21

what is a java identifier

Answer 21

this is the name of a 
variable
method
class
interface
package

Question 22

what does a java identifier have to begin with

Answer 22

a letter : example
a $ symbol $example
a _ symbol _example

Question 23

what are the special rules regarding numbers in identifier

Answer 23

they can be used in a identifier but can not be used as the first character.

not valid : 1example
valid example : example2

Question 24

Can a single _ (underscore) be used as a identifier

Answer 24

no, this is not allowed in versions after java 9

Question 25

can you use java reserved words as identifiers?

Answer 25

No you can not | Since java is case sensitive you could use "CLASS" but you can't use "class" Don't do this, even if you can

Question 26

what are the allowed characters to be used in a identifier

Answer 26

the only allowed characters for identifiers are all alphanumeric characters([A-Z],[a-z],[0-9]), ‘$‘(dollar sign) and ‘_‘

Question 27

what are the common conventions around camelCasing in identifiers

Answer 27

method and variables are writtin in camelCase with the first letter being lowercase likeThisExample class and interface names are written in camelCase with the first letter being uppercase LikeThisExample

Question 28

``` how many variables are declared and initialized in this statement { String s1, s2; String s3 = "yes" , s4 = "no"; int i1, i2, i3 = 0; } ```

Answer 28

4 are declared s1, s2, i1, i2 3 are initialized s3, s4, i3

Question 29

``` which of the following are legal declarations 1 boolean b1, b2; 2 String s1 = "1", s2; 3 double d1, double d2; 4 int i1; int i2; 5 int i3; i4; ```

Answer 29

1 : legal 2 : legal 3 : NOT LEGAL - you can't declare 2 var types in the same statement even if they are the same types. double d1, d2; would be legal 4 : legal 5 : NOT LEGAL - this line has 2 statements, and one does not have a var type. int i3; int i4; would be legal

Question 30

When must a variable be initialized

Answer 30

BEFORE using it.

Question 31

where can you use a local variable

Answer 31

inside of a constructor, method or initializer block

Question 32

where are instance variables used

Answer 32

this variable is part of one object.

Question 33

where are class variables used

Answer 33

This variable can be used by all instances of a class. It can also be used outside of the class without a active instance of the class.

Question 34

``` does this compile public class VarKeyWord { var tricky = "Hello"; } ```

Answer 34

NO, that will not compile | tricky is a instance variable and the var keyword can only be used for local variables.

Question 35

what happens when you use the var keyword as a variable type when declaring and initializing a variable.

Answer 35

This can only be done for local variables and it tells java to infer the type of the variable based on the first value.

Question 36

Can a local variable that has been initilized using var change its type

Answer 36

no, it cannot.

Question 37

does this compile { var question; quesiton = 1; }

Answer 37

``` No. To declare a var variable it has to be initialized in the same statement. this would compile: var question = 1; or var question = 1; ```

Question 38

why does this not compile public int addition (var a, var b){ return a + b }

Answer 38

because the var keyword can not be used for method parameters. It can only be used for a local variable

Question 39

``` does this compile public class var { public var() { } } ```

Answer 39

``` Does not compile var is not a reserved word, but it is a reserved type. So it can not be used to to define a type such as class interface enum ```

Question 40

when does a local variable go out of scope

Answer 40

At the end of the code block where the variable has been declared.

Question 41

when does a instance variable go out of scope

Answer 41

when the parent object is eligible for garbage collection

Question 42

when does a class variable go out of scope

Answer 42

in scope from declaration until program ends