Java Unit 2 Before we discuss methods we should talk briefly about objects since methods are part of objects Objects Chicken yeller new Chicken yeller is a Chicken reference ID: 187535
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Slide1
Methods
Java Unit 2Slide2
Before we discuss
methods,
we should talk briefly about objects since methods are part of objects.
ObjectsSlide3
Chicken yeller =
new
Chicken();
yeller
is a Chicken
reference.
Instantiating ObjectsSlide4
Chicken yeller =
new
Chicken();
Instantiating Objects
yeller
0x234
0x234
Chicken
new Chicken()
creates a new Chicken Object out in memory.
yeller
stores the
location
of that new Chicken Object.Slide5
A
method usually
performs
a specific task by activating
the code inside the method
.
Methods can return a value
Return
type can be an intrinsic type
(
int
, double, etc.) or
an object (such as Chicken or String).
Example: public int getAge()
{ return age;
}
MethodsSlide6
Use the keyword
void
if a value is not to be returned by the method.
For example:public void speak()
{
System.out.println("cluck-cluck");}
Void MethodsSlide7
Methods can accept
parameters
A
parameter is an object you pass in to the method when you call
it.
Parameters
follow the same naming conventions as field
names.
For example:
public void
setAge
(
int a)
{ age = a;}
Method ParametersSlide8
A primitive data type gives the method a copy of its value. The method does not have access to the original data
.
An
object gives the method a copy of its reference that points to methods for changing object data. A method can change the data stored in an object because the method has access to the object's methods
.
We will revisit this concept later.
Passed by ValueSlide9
More than one method of the same name can be included in a class
The compiler uses the types, order, and number of parameters to determine which method to
execute
This allows us to use methods with
optional
parameters.
Method OverloadingSlide10
Methods have a signature that follows this structure.
Method Signatures
return type
name
params
code
access
public
void
speak
( )
{
System.out.println
("cluck-cluck");
}Slide11
Public
access simply means the member can be used anywhere inside or outside of the class.
Private access means that method can only be accessed within the class it is defined in.
Access
accessSlide12
Accessor
methods
(getters) return information, and are named accordingly:
getAge
()
getAccountBalance
()
Mutator
methods (setters)
modify the state of the
object and are named accordingly.
setAge()addDeposit()
Accessors
and Mutators(Getters and Setters)
This allows for Data Hiding, and important concept in OOP.Slide13
called from within the class by other methods
private
access
Helper MethodsSlide14
are special methods
that
create
an instance of your class.
always
have the same name as the
class.
never have a return type.
are
used to initialize all of the data/properties inside the
class.
ensure
that the Object is ready for use.
Constructors:Slide15
A
default
constructor:
Is provided by the compiler if you do not provide
one
Takes no parameters
Default ConstructorSlide16
Static members belong to the class and are shared by all instances of the class
.
Declared using the
static keyword
Can be accessed without an instance of the class
Static Methods Slide17
Is a self-reference to the current
object
Provided
only in instance methods, not in static methods
thisSlide18
Documenting
Methods
Methods should be carefully commented so that a reader of the program understands what task the method is performing and what data, if any, will be returned by the method
Method documentation should appear just above a method
Documentation should include a brief description of the method, any preconditions, and the
postconditionSlide19
Preconditions
and
Postconditions
The precondition states what must be true at the beginning of a method for the method to work properly.
The postcondition states what must be true after the method has executed if the method has worked properly.
Preconditions and postconditions should not state facts that the compiler will verify. They should also not refer to variables of information outside the method.
The postcondition should not state how the method accomplished its task.Slide20