Chapter 3 - Classes some basics

Question 1

what is a class in terms of type

Answer 1

- A class is a special kind of programmer-defined type,
and variables can be declared of a class type
- A value of a class type is called an object or an
instance of the class

Question 2

primitive vs class type values

Answer 2

• prim -sinlge piece of data
• classes - multiple pieces of data as well as methods
• All instances of a class have the same methods
  – All instances of a class have the same pieces of data (i.e.,
  name, type, and number)
  – For a given instances, each piece of data can hold a
  different value

Question 3

what are the contents of class definition?

Answer 3

• specifies that data items and the methods that all of its objects will have
• data items - fields - instance variables

Question 4

how to invoke a method

Answer 4

use the calling object and the mthod name

classVar.mymethod();

Question 5

two method categories

Answer 5

• perform action - dont return, void

- compute and return a value

Question 6

keywords used for methods

Answer 6

typeReturned methodname

void
main

Question 7

turning a method into a void method

Answer 7

objectName.returnedValueMethod()

Question 8

local variable

Answer 8

variable declared within a method definition

Question 9

examples of local variables

Answer 9

• declared in the main method
• method parameters
• If two methods each have a local variable of
  the same name, they are still two entirely
  different variables
• for loop

Question 10

formal parameters

Answer 10

some methods need additional data via a list of parameters in order to perform their work

Question 11

what does a parameter list do

Answer 11

A parameter list provides a description of
the data required by a method
– It indicates the number and types of data
pieces needed, the order in which they must be
given, and the local name for these pieces as
used in the method

Question 12

what are arguments

Answer 12

actual parameters
when a method is invoked, the appropriate values must be passed in the form of arguments
number and order must match that of the para list
type of each argument must be compatible with that of the corresponding parameter

Question 13

call by value mechanism

Answer 13

Call by Value means calling a method with a parameter as value. Through this, the argument value is passed to the parameter.

Question 14

pass by reference vs pass by value

Answer 14

Pass by Value: The method parameter values are copied to another variable and then the copied object is passed, that’s why it’s called pass by value.
Pass by Reference: An alias or reference to the actual parameter is passed to the method, that’s why it’s called pass by reference.

Question 15

what happens if arguments and parameters dont match

Answer 15

java will try an automatic type conversion

Question 16

what is a constructor?

Answer 16

A constructor is a special kind of method that
is designed to initialize the instance variables
for an object:

Question 17

the this keyword in constructors

Answer 17

this refers to the instance variables e..g this.word (instance variable word) = word

Question 18

what is overloading?

Answer 18

when two or methods in the same class have the same name - to be valued they must have different signatures(i.e. their parameter list must differ) - they cant have different return types

Question 19

what are the default variable declarations

Answer 19

boolean - false
class type - null
string - ""

Question 20

accessor and mutator methods

Answer 20

public String getString(){return String;}

public void setName(){this.name = name;}

Question 21

describe an encapsulated class

Answer 21

implemented details hidden in the capsule
-private instance variables
-private constants
-private methods and bodies f public and private method definitions
interface available to a programmer using the class :
- comments
-headers of methods
-public defined constants
a class definition should have no public instance variables

Question 22

public vs private modifiers

Answer 22

public - no restrictions on where an instance variable or methods can be used
private - instance variable or method cannot be accessed by name outside the class, private methods are typically helper methods

Question 23

each class typically needs to have its own….methods

Answer 23

toString and equals

Question 24

example of a toString method

Answer 24

public String toString(){return “Name:”+”name”}

Question 25

example of an equals method

Answer 25

publicbooleanequals(ObjectanObject){if (this==anObject){ //are the two objects in the same memory location?returntrue;}

//another part of the method must be written to check that the thing is equal but not necessarily in the same memory location