1!
1!
CS1110 Classes, stepwise refinement 25 Sep 2008!
Rsrecah on spleilng!
Aoccdrnig to a rscheearch at Cmabirgde Uinervtisy, it deosn't
mttaer in waht oredr the ltteers in a wrod are, the olny
iprmoetnt tihng is that the frsit and lsat ltteer be at the rghit
pclae. The rset can be a total mses and you can sitll raed it
wouthit porbelm.Tihs is bcuseae the huamn mnid deos not
raed ervey lteter by istlef, but the wrod as a wlohe.!
Miscellaneous points about classes.!
More on stepwise refinement.!
Prelim 7:30-9:00 Tuesday, 30 Sept., Philips 101!
Review session: 1:00-3:00, Sunday, 28 Sept., Philips 101!
2!
Help: Get it now if you need it!!!
• One-on-one help from TAs. For info, get on the course
website and click "Staff-info".
• Call Cindy Pakkala 255-8240 for an appointment with Gries.
• See a consultant in the ACCEL Sun, Mon, Tues, Wed, Thurs
4:00pm to 11:00pm.!
• Peer tutoring (free). On http://www.engineering.cornell.edu,
click on "student services". On the page that comes up, click
on ”Engineering Learning Initiatives (ELI.) in the left column,
upper part. Then, click on "peer tutoring" in the left column.
• Take an AEW courses. Ask in Olin 167.
3!
Content of this lecture!
This lecture contains some final miscellaneous points to round out
your knowledge of classes and subclasses. There are a few more
things to learn after this, but we will handle them much later.
• Inheriting fields and methods and overriding methods.!
Sec. 4.1 and 4.1.1: pp. 142–145!
• Purpose of super and this. Sec. 4.1.1, pp. 144–145.!
• More than one constructor in a class; another use of this.!
Sec. 3.1.3, pp. 110–112.!
• Constructors in a subclass —calling a constructor of the!
super-class. Sec. 4.1.3, pp. 147–148.!
4!
Employee c= new Employee(“Gries”, 1969, 50000);!
c.toString()!
a0!
Object!
name!“Gries”!start!1969!
salary!50,000.00!
getName() setName(String n) …!
toString()!
equals(Object) toString() !
Employee!
c!a0!
Which method toString()
is called?!
Overriding rule or!
bottom-up rule:"
To find out which is used,
start at the bottom of the
class and search upward
until a matching one is
found.!
Terminology. Employee inherits methods and fields from
Object. Employee overrides function toString.!
Sec. 4.1,
page 142!
This class is on
page 105 of the
text.!
5!
Purpose of super and this!
this refers to the name of the object in which it appears.!
super is similar but refers only to components in the partitions above.!
/** = String representation of this
Employee */!
public String toString() {!
return this.getName() + ", year ” +"
getStart() + ", salary ” + salary;!
} !
ok, but unnecessary!
/** = toString value from superclass */!
public String toStringUp() {!
return super.toString();!
}!
necessary !
Sec. 4.1, pages
144-145!
a0!
Object!
name!“Gries”!
start!1969!
salary!50,000.00!
getName() "
setName(String n) {…}!
toString()!
toStringUp() { …}!
equals(Object) "
toString() !
Employee!
6!
A second constructor in Employee"
Provide flexibility, ease of use, to user!
/** Constructor: a person with name n, year hired d, salary s */!
public Employee(String n, int d, double s) {!
name= n; start= d; salary= s;"
}!
/** Constructor: a person with name n, year hired d, salary 50,000 */!
public Employee(String n, int d) {!
name= n; start= d; salary= 50000; !
}!
First constructor"
Second constructor;
salary is always 50,000"
/** Constructor: a person with name n, year hired d, salary 50,000 */!
public Employee(String n, int d) {!
this(n, d, 50000); "
}!
Another version of second
constructor; calls first constructor"
Here, this refers to the other constructor.
You HAVE to do it this way !
Sec. 3.1.3,
page 110!
