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A^ bit^
about
testing
Test case
: Set of input values, together with the expected output. Develop test cases for a method from its specification --- evenbefore you write the method
’s body.
/** = number of vowels in word w.Precondition: w contains at least one letter and nothing but letters*/ public^ int
numberOfVowels(String w) {… }
Developing testcases first, in “critique”^ mode, canprevent wasted workand errors.
How^ many
vowels^
in^ each^ of
these^ words?
creek syzygy
Test^ cases
for^ number
of^ children
“Child 2” mom pop^ j0 children w0 0 name
BFly s0^ “Mumsie
” null mom^
popnull children^1 name
BFly j
“Opa” mom pop null children
null 1 name
BFly “Popsi b ” null mom^
b0pop children^2 name
BFly w
“Child 1” mom pop null children
w L0 name
BFly^1 If L0 gets a mom,say j0, the mom’snumber of childrenmust increase.You should test this.
Class^
Object:
the^ superest
class
of^ them
all
Java:^ Every
class^ that
does^ not extend^ another
extends
class
Object.^
That^ is, public class^ W^ {…} is^ equivalent
to public^ class
W^ extends
Object^ {…}
W@af
W
lname^
“Obama
ssn^123456789 boss^
null W(…)^ getLname() getSsn(),
getBoss()
Object setBoss(W) toString() equals(Object)
hashCode() Should^ draw
object^ like
this
We^ often
leave^ off
the^ top partition
to^ reduce
clutter; we
know^ that
it^ is^ always
there
Method
toString
Object W@af^ lname^
“Obama
ssn^123456789 boss^
W null getSsn()
toString()
toString()
in^ Object
returns the^ name
of^ the^ object:
W@af
Java Convention
: Define toString() in any class to return a representation ofan object, giving info about the valuesin its fields.New definition of toString()
overrides
the definition in partition Object
c^ W@af toString()^
c.toString()
calls^ this
method In appropriate places, the expressionc^ automatically does c.toString()
Another
example
of^ toString()
/** An instance represents a point (x, y) in the plane */ public class
Point { private^
int^ x; // x-coordinate private^
int^ y; // y-coordinate … / = repr. of this point in form**
“ (x, y) ”
public^ String
toString() { return^ “(” + x + “, ” + y + “)”;} }
Point@fa
Point x^9
y^5
Function toString should give the values in thefields in a format that makes sense for the class.
(9,^ 5) docsity.com
Intro^
to^ static
components
W@af
W
lname^ “
Om” boss null ssn^35 isBoss(W)
W@b
W
lname^
“Jo” boss W@af ssn^21 isBoss(W)
/** =^ “this object is c
’s boss”
Pre: c is not null. */ public^ boolean
isBoss(W c) { return this
== c.boss; } keyword
this^ refers to the name of the object in which
it appears
x.isBoss(y) is
false y W@af y.isBoss(x) isx W@b
true
Intro^
to^ static
components
W@af
W
lname^ “
Om” boss null ssn^35 isBoss(W)
W@b
W
lname^
“Jo” boss W@af ssn^21 isBoss(W)
/** =^ “b is c
’s boss”
Pre: b and c are not null. */ public^ static
boolean
isBoss(W b, W c) { return^ b == c.getBoss();}
isBos(W,W)
W@afy x^ W@b
static:^ there
is^ only^ one copy^ of^
the^ method.
It is^ not^ in
each^ object W^ (objects,
static components)
x.isBoss(x,
y) y.isBoss(x,
y) Preferred: W.isBoss(x,
y)
Java^ application
Java^ application:
bunch
of^ classes
with^ at
least^
one^ class
that^ has
this
procedure:^ public
static
void^ main(String[]
args)
{^ …^ }
Type^ String[]:
array^ of elements
of^ type^
String. We^ will^
discuss^ later
Running
the^ application
consists
of^ calling
that^ method
main
Convention:
the^ method
main^ doesn’t
use
parameter
args,^ then
call^ it^ with
argument
null
