Transcript Slides_12

BIT 115: Introduction
To Programming
Professor: Dr. Baba Kofi Weusijana
(say Doc-tor Way-oo-see-jah-nah,
Doc-tor, or Bah-bah)
[email protected]
http://edutek.net/cascadia/bit115
BIT 115: Introduction To Programming
Quiz 12
•https://catalysttools.washi
ngton.edu/webq/survey/b
abaw/55235
• Due to Java Code Critic by 11:15 AM!
BIT 115: Introduction To Programming
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Quiz
•
•
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More “write me some code” type quizzes
This sort of thing will be on the final
…and in real life, of course!
–
we have to be fast developers, so we can't always
wait for the computer to catch every little mistake
– Little mistakes can lead to big confusion!
we must be able to try out several designs in our head
before typing any one of them up
–
•
How to practice doing this:
–
–
Write parts of your homework on paper first
Then type it in, see what you did wrong!
BIT 115: Introduction To Programming
•
We’ve sometimes included this for instructional purposes
• public void turnAround()
• {
•
this.turnLeft(); // You almost never need "this" for a method call.
It's just clutter.
• You can just use:
• public void turnAround()
• {
•
turnLeft(); // this will call the closest method in the inheritance
hierarchy
• Avoid infinite recursion!
• public void turnAround()
• {
•
some.parent.turnAround(); // this is fine
•
turnAround(); // Avoid
calling
your
own method!
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Introduction
To Programming
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Convert MS Excel Files
• If you have turned in an .xlsx file, convert it
to .xls and email it to me.
• So far I can convert .docx files to .rtf
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Today
• Chapter 3.6
– public, private, protected, package-private
• Programs in multiple files
• Non-Robot software
• Unit Testing
– Using JUnit with Eclipse
BIT 115: Introduction To Programming
Next Lecture
• Ch 5.4.1-5.4.3 = Complex boolean expressions
• Ch 5.5.1-5.5.4 = For loops, Do...while loops
• Ch 2.4.3-2.4.4 = Documentation; JavaDoc
BIT 115: Introduction To Programming
Predicate Methods & Return
• OK
•
•
•
•
•
•
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public boolean isRobotOnAvenueFive()
{
if (this.getAvenue() == 5)
{
return true;
}
else
{
return false;
}
}
• BEST (simpler)!
•
•
•
•
public boolean isRobotOnAvenueFive()
{
return this.getAvenue() == 5;
}
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Return
• Return can also be used in void methods to indicate that you simply
want to stop the method & return to the caller
–public void doNothing()
• {
• return;
• System.out.println(“Never say this.”);
• }
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Access Modifiers for Classes,
Methods, & Objects
• public: anybody can call this method
– Good for methods and constants that we want to make
widely available
• private: nobody (except other methods in the
same class) can access this
– Good for helper methods (see pattern 3.8.1 p. 155-156)
– HOWEVER, private methods aren't made available to
classes that inherit from this class, either (subclasses)
• protected: like private, except that subclasses
can call the method (see Robot.breakRobot()
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Access Modifiers for Classes,
Methods, & Objects
• no modifier (default/package-private):
nobody (except other methods in the same
package) can access this
– Packages are named groups of related classes
– Not in textbook: see link on next slide
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Access Levels
Modifier
Class
Package
Subclass
World
public
Yes
Yes
Yes
Yes
protected
Yes
Yes
Yes
No
no modifier
(packageprivate)
Yes
Yes
No
No
private
Yes
No
No
No
• See:
http://java.sun.com/docs/books/tutorial/java
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Access Modifiers for Classes,
Methods, & Objects
• In general declare everything private
– UNLESS you want to make it available to
anybody
• public
– UNLESS you want to make it available to
subclasses
• protected
– UNLESS you want to make it available to its
package
• no modifier (package-private)
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Why hide (encapsulate)?
• Why would you want something that's private?
– Other parts of the program can't manipulate.
– Fewer bugs, but isn't any more secure.
• The main advantage is that other code won't
accidentally change your object's internal data.
– This idea is called encapsulation: the internal, private,
state of an object isn't accessible to other parts of the
program, but the public interface is available.
– Public code limits you to a particular implementation and
limits your flexibility to change your code later.
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encapsulate |enˈkaps(y)əˌlāt|
• verb [ trans. ]
• enclose (something) in or as if in a capsule.
• • express the essential features of (someone or
something) succinctly : the conclusion is encapsulated
in one sentence.
• • Computing enclose (a message or signal) in a set of
codes that allow use by or transfer through different
computer systems or networks.
• • Computing provide an interface for (a piece of
software or hardware) to allow or simplify access for
the user.
• • [as adj. ] ( encapsulated) enclosed by a protective
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coating or membrane.
ICE 12 Part 1: public, private,
protected
• About 5 minutes, must finish by 11:50 AM
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ICE12 Part 2: Putting Classes in
Separate Files
• About 5 minutes, must finish by Noon
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ICE 12 Part 3: Non-robotic
Software
• static classes/methods/objects: Always have the
same value within a Java Virtual Machine (Java
VM)
• Open the ICE_12.java. Note that the main method
is always a static method: It can be called on a
class without instantiating an object first
– Can only call static methods or make objects and call
their non-static methods
– Useful for instantiating objects including those of it’s
own class, often done to get things going in a program
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final and static keywords
• final keyword means the value never
changes once it is set
– final classes can’t have any subclasses
• final static objects thus never change and are
called constants
– constants’ names should be in all caps
– public static final Direction EAST
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ICE_12.java: main & println
• Does not import any robot classes
• Has a main method so it can be run as Java
application
– Uses default system output (using
System.out.println(“…”)). This is fine because
the System.out object is static and its println
method is public.
– However the ICE_12.countdown() method is not
static, so it is only callable from the static main method if
it is being called on an existing object. So an ICE_12
object called runningObject is instantiated so that
runningObject.countdown() can be called.
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ICE 12 Part 4: Using println for
debugging, using JUnit for testing
– Test the ICE_12.countdown() method
using JUnit 4
– Fix the ICE_12.countdown() method and
see how JUnit confirms that it is fixed
– Writing test cases is crucial for applications
people will use
• Allows software developers to change an
application without fear of missing the reoccurrence
of old bugs!
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A03 Groups
• Who doesn’t have a partner?
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