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BIT 115: Introduction To
Programming
LECTURE 3a
Instructor: Craig Duckett
[email protected]
Lecture 3 Announcements
• By now everyone should be up and running with Java, jGRASP, and
the Becker Robots on their home or personal computers.
• Any Problems?
• Has everyone had a chance to work with the Java programs and the
Becker Robots?
Reading Assignment for Today
• Appendix F.1 – Extending a Class
• Chapter 2.1, 2.2 – Extending Robot Class
• Chapter 2.4 – Coding Style
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H Assignment 1 is due LECTURE 4
th
•
Wednesday,
July
15
O
M
– It’s posted on the website under Assignments menu
– It will be due by midnight
E
• If unsure how to upload to StudentTracker, then bring your
work to class, in electronic form, and we will go over how to
W
hand in the homework:
Student Tracker
O
How to Use Student Tracker
R • If you’re stuck, seek help
– Talk to the Instructor or a classmate
K
– Email me
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Assignment Announcements
• Assignment 1 DUE Lecture 4, Wednesday, July 15th, by midnight
• Assignment 2 DUE Lecture 7, Monday, July 27th, by midnight
• Assignment 1 Revision DUE Lecture 8, Wednesday, July 29th, by
midnight
• Assignment 2 Revision DUE Lecture 10, Wednesday, August 5th,
by midnight
• Assignment 3 DUE Lecture 11, Monday, August 10th, by midnight
• Assignment 3 Revision DUE Lecture 13, Monday, August 17th, by
midnight
• Assignment 4 DUE Lecture 15, Monday, August 24th, by midnight
NO REVISION AVAILABLE
• Extra Credit 01 DUE Lecture 15, Wednesday, August 26th, by
midnight
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Lecture Setup Strategy
Some Lecture we will have one long lecture followed by one long ICE period, so
the class will basically only be divided into two parts: Lecture and ICE.
Other Lectures, like today’s lecture, will be divided into four (4) parts: Lecture,
ICE, Lecture, ICE. You can tell if it is going to be a four part class by seeing if
there are two lecture PowerPoints offered (for example , Lecture 03a and
Lecture 03b)
The schedule for four part classes will be as such (approximately):
• Lecture (a): 45 minutes – 11:30am-12:15pm
• ICE (a): 45 minutes – 12:15pm-1:00pm
• Lecture (b): 45 minutes – 1:00pm-1:45pm
• ICE (b) 45 minutes – 1:45pm-2:30pm
NOTE: Times may vary according to this scheme, although this is the working
plan on how I will try to divide the class when there are two lecture points.
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And Now…. The First Quiz!
• You each get a hand-out: Put your name on it
• When your program works, raise your hand
– 5 minute limit
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Lecture 3
Buckle up! This could really zoom-zoom-zoom!
• Extending a Class : Creating a new type of Robot
(Predicting What A Program Will Do BEFORE you Run It)
• Style and Java Coding Conventions (If time)
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Appendix F.1, Chapter 2.1, 2.2
Extending a Class
•
•
•
•
•
Extension (B extends A)
Extending the Robot Class
Superclass and Subclass
Constructor
Adding a Service
• turnAround();
• turnRight();
• The This Keyword (Implicit Parameter)
• Putting It All Together
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Constructor
Here, when we create a new instance (an object) of the Robot class, a ‘hidden’ default
constructor works in the background to make sure that Kelsey inherits all the attributes and
methods available to Robots, including its placement on a particular Street and Avenue and
Direction in a particular City, and that it can use all of the actions (methods) available to the
Robot class (including move(), pickThing(), turnLeft(), putThing(), frontIsClear(), etc.)
http://faculty.cascadia.edu/cduckett/bit115/Becker/Documentation/index.html
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Constructor
Constructors have one purpose in life. To create an instance of a class. This
can also be called creating an object, as in:
The purpose of a method, by contrast is much more general. The purpose of a
method is to execute Java code, to allow the object to do something.
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Now … what if these is an action that you might want Kelsey to do that isn’t
found in the Robot class?
For instance, instead of invoking the the turnLeft() method three times, you
could just call up a turnRight() ?
The problem is, the Robot class does not have a turnRight() command
(method). The Robot class has been finalized. You cannot add to it.
The good news is, you can create a new method like turnRight() that will do
what you want the robot to do!
But in order to make this happen, you need to extend the Robot class …
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Extending a Class:
Where ClassB extends ClassA
In Plain Ol’ English: Where ClassB “inherits” the attributes and actions of ClassA
… then adds new functionality to them.
When we’re not interested in extending a class because we’re happy with the
methods that come with that class just the way they are, then we declare our class the
‘normal’ default way: public class Example extends Object
Object is the top class of all class hierarchies. When a new
instance of anything is made in Java, then it inherits all the
attributes and actions of the Object class. You can’t get a new
object without Object.
Object
Class
Hierarchy
However, if we want to add new functionality (methods) to the Robot class (like
turnRight) then we need to extend the Robot class (which is itself an extension of
Object)
public class MrRoboto extends Robot
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Extending a Class:
Where ClassB extends ClassA
Instance vs. Extension?
Instance creates a new object from a class, but extension extends a new
class from a class through inheritance, allowing for an improved class that
might offer additional attributes and services (methods) not available in the
original class …
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Extending the Robot Class
public class MrRoboto extends Robot
MrRoboto
extends
inherits
Robot
MrRoboto “inherits” all of
the Robot attributes and
services and then can have
additional attributes and
services of its own (i.e.,
those not shared by Robot).
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Superclass and Subclass
Robot
Superclass
MrRoboto
Subclass
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Constructor
import becker.robots.*;
public class MrRoboto extends Robot
{
public MrRoboto(City theCity, int street, int avenue, Direction aDirection)
{
super(theCity, street, avenue, aDirection);
}
//New service or services go here
}
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Constructor
import becker.robots.*;
public class MrRoboto extends Robot
{
// This declares the parameters used by Robot “inside” of MrRoboto
public MrRoboto(City theCity, int street, int avenue, Direction aDirection)
// This passes on information received by the parameters used by Robot ‘inside” of MrRoboto
{
super(theCity, street, avenue, aDirection); //Instead of Robot here, Java uses the keyword super
}
//New service or services go here
}
Constructors fulfill a special roll. They are responsible for ensuring an object is set up properly when
it is created, and that it can be immediately used once it is created. This construction process is
known as initialization. Two other details about constructors: they must have the same name as the
class and they do not have a return type, not even a void.
NOTE: We will talk briefly about return types in just a few minutes, and go over them in greater detail in an upcoming
lecture.
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Constructor
public class MrRoboto extends Robot
{
public MrRoboto(City theCity, int street, int avenue, Direction aDirection)
{
super(theCity, street, avenue, aDirection);
}
}
MrRoboto
Robot
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Constructor
public class MrRoboto extends Robot
{
public MrRoboto(City theCity, int street, int avenue, Direction aDirection)
{
super(theCity, street, avenue, aDirection);
}
}
MrRoboto
Robot super
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Constructor
public class MrRoboto extends Robot
{
public MrRoboto(City theCity, int street, int avenue, Direction aDirection)
{
super(theCity, street, avenue, aDirection);
}
}
MrRoboto
 imagine a conduit …
super
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Constructor
public class MrRoboto extends Robot
{
public MrRoboto(City theCity, int street, int avenue, Direction aDirection)
{
super(theCity, street, avenue, aDirection);
}
}
bothell, 3, 2, Direction.SOUTH
MrRoboto
super
BIT 115: Introduction To Programming
Since MrRoboto is inheriting the
Robot parameters, the Robot still
needs those parameters in order
for MrRoboto to inherit them.
This is why it appears as if there
are two sets of parameters: one
set to pass through MrRoboto, a
second set for Robot to receive
them, where Robot sends them
back to MrRoboto by extension.
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Adding New Services
public void turnAround()
{ this.turnLeft();
this.turnLeft();
}
public void move3()
{ this.move();
this.move();
this.move();
}
.
public void turnRight()
{ this.turnAround();
this.turnLeft();
}
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The this keyword
The new Java feature in the new services we created is the use of the
this keyword.
The keyword this is useful when you need to refer to an instance of the
class from its method, but without having to refer to it by a specific
name. Why? Because when you create the new method, you don’t
know the name of the particular robot that is going to use it, so ‘this’ is
a kind of placeholder name.
The this keyword helps us to avoid name conflicts, and also creates a
shortcut to having to invent a unique name for each field in the
different methods.
public void turnAround()
{ this.turnLeft();
this.turnLeft();
}
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Putting It All Together
Two Ways of Doing the Same Thing
Version 1: One Class
MrRoboto.java
Version 2: Two Classes
MrRobotoMain.java
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Putting It All Together
MrRoboto2.java
MrRoboto.java
MrRobotoTest2.java
All on One File
On Two Separate Files
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Chapter 2.4 – Coding Conventions (Style)
http://www.oracle.com/technetwork/java/codeconv-138413.html
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ICE Strategy
For the BIT115 class, you do not have to submit the ICES, rather you will show me InCLASS that you have finished with them and I will give you credit for them right then
and there. If you worked on the ICEs in-class, but did not finish them, you will still get
full credit for working on them as long as you were in class trying.
The In-Class Exercises have been designed to help you acquire the coding know-how
you need to successfully complete the Assignments. As such, if you do not finish your
ICEs in class, it is HIGHLY RECOMMENDED that you finish the ICEs outside of class on
your own time because it will make your problem-solving of the Assignments that
much easier.
Starting with today’s ICE 03b I will start posting “solutions” to the ICEs two days after
the ICE. This means I will post solutions to Monday ICEs by Wednesday, and solutions
to Wednesday ICEs by Friday. Please use these “solutions” as you see fit. Once again,
they have been designed to help you specifically “solve” the upcoming Assignment.
Finally, going forward, the ICE number will not coincide with the Lecture number, as
some lectures have multiple ICEs and the ICEs are numbered in consecutive order to
follow one after the other. As the quarter progresses the ICE number will move
further and further away from the Lecture number. For example, Lecture 14 has an
ICE 19.
Lecture 3a ICE:
Creating a New Type of Robot
Approximate Time: 12:15 to 1:00pm
•ICE_03_Demo_1.java DEMO
•In-Class Exercise Directions
•ICE_03_01_Trace.java
•ICE_03_02_CompileErrors.java
•ICE_03_03_WalkDownWalls.java
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