Learning Unit 2 Programming Theory

Question 1

In Java

Answer 1

Each variable has a data type.

Question 2

Data types commonly used:

Answer 2

• Integers (whole numbers)
• Real numbers (numbers with decimals)

Question 3

Important to tell Java what data type a variable will be so

Answer 3

It knows how much space in memory to allocate for each variable.

Question 4

For input

Answer 4

showInputDialog method of JOptionPane class.

Question 5

= means

Answer 5

It gets the data or is assigned a value.

Question 6

Strings

Answer 6

Are enclosed in double quotes.

Question 7

String is

Answer 7

• A class
• An object

Question 8

All classes start with

Answer 8

A capital letter.

Question 9

A variable can be

Answer 9

Joined/concatenated to a text String using a + (plus) sign.

Question 10

Assignment statement contains

Answer 10

An equals sign.

Question 11

The subject variable

Answer 11

Has been assigned (or gets) a value.

Question 12

The value that is assigned

Answer 12

Has been produced (returned) by the showInputDialog method.

Question 13

The 2 main types of variables used in Java

Answer 13

• Primitive data type
• Object reference

Question 14

Difference

Answer 14

Objects are stored differently in memory to primitive data types and different behavior.

Question 15

No real difference between

Answer 15

The way the primitive and objects are declared (must specify type and give variable a name).

Question 16

Several variables of same type

Answer 16

Can be declared at the same time (use of commas).

Question 17

After the variable has been declared

Answer 17

It must be initialized.

Question 18

If you use a variable without initializing

Answer 18

The compiler generates an error.

Question 19

The only object that can be declared & initialized like primitive types

Answer 19

Because it is so commonly used in programs.

Question 20

Important to declare variables once

Answer 20

Cannot be 2 boxes in memory with the same identifier.

Question 21

Ever variable has 3 characteristics:

Answer 21

• Identifier/name
• Data type: Stating what type of data can be stored in it.
• Value that is stored in it.

Question 22

In a program every variable that is used must be:

Answer 22

• Declared (created) given a identifier and a data type.
• Given a value: This is done using assignment statement.

Question 23

String data is text data

Answer 23

That cannot have arithmetic calculations carried out on it.

Question 24

To input numbers

Answer 24

Convert the data from a string to an integer or real type.

Question 25

Strings are enclosed in double quotes

Answer 25

So that Java identifies the data type and knows what operations can be performed on it.

Question 26

String cannot be placed in a variable type int

Answer 26

As the are incompatible types (they are not stored the same way in memory).

Question 27

+ Operator can perform different functions (joining or adding)

Answer 27

Depending on the types of the variables or values on either side of the + sign.

Question 28

int is not a class but

Answer 28

Is one of the primitive data types.

Question 29

Long ago programmers stored real numbers as either

Answer 29

Single precision or double precision (single or double for short).

Question 30

Double precision could

Answer 30

Store real numbers more accurately, therefore double type remained.

Question 31

Integers are

Answer 31

A sub-set of real numbers.

Question 32

Simple assignment operator is

Answer 32

=

Question 33

Direction of assignment

Answer 33

Right hand side of = to left; variable on left changes.

Question 34

Java expects

Answer 34

A single variable on left-hand side.

Question 35

Compound operator

Answer 35

Uses double symbols.

Question 36

The computer works out arithmetic expressions in this order

Answer 36

First: Brackets Second: *,/ (integer and real division), % Third: +, -

Question 37

Variables can be declared

Answer 37

At the beginning of a method/the first time they are used in a program.

Question 38

Useful to declare variables at the beginning of method

Answer 38

Gives a summary of variables that are going to be used in the method.

Question 39

It is essential

Answer 39

To follow the rules for identifier names.

Question 40

Conventions make your program

Answer 40

Readable for other people and easy to understand.

Question 41

Rules for variable names/identifiers

Answer 41

- Can contain numbers but may not start with a number. - Spaces are not allowed. - No special characters may be used. - Reserved words (keywords that have a special meaning in Java) may not be used.

Question 42

By convention

Answer 42

- Identifiers of variables and methods in Java start with lowercase letters. - Identifiers that are names of classes start with a capital letter. - Identifier should reflect the contents of the variable, method/class. - Any identifier that contains more than one word must have the words joined together using camel case, to make identifiers more readable.

Question 43

Eg. of primitive data types

Answer 43

- int - double - char - boolean - byte - short - long

Question 44

Char variable in Java is

Answer 44

- Enclosed in single quotes - Represented with Unicode instead of ASCII code.

Question 45

First 127 characters of

Answer 45

Unicode and ASCII are the same.

Question 46

Values can be assigned

Answer 46

To variables in a program in an assignment statement.

Question 47

Java provides

Answer 47

Addition (+), subtraction (-), multiplication (*) integer and real division (/) and modulus (%).

Question 48

Plus operator is overloaded

Answer 48

Can add numbers together and join strings.

Question 49

Subtraction and multiplication

Answer 49

Perform as expected, not overloaded.

Question 50

Division can be used with integer and double

Answer 50

Produces different results depending on the type of data in which it is used.

Question 51

Java has a mod operator

Answer 51

Depicted with a % sign

Question 52

DIV (integer division) and division operator

Answer 52

Depends on types you are working with.

Question 53

int/int =

Answer 53

(Integer division) int and remainder is ignored.

Question 54

(Real division) real

Answer 54

As long as one of the numbers in the division is declared as double, ans. will be real and should be assigned to variable declared as double.