Transcript 2-4-or-3-1-other

CS12230
Introduction to Programming
Lecture 2or3-Other things
1. Reading from Keyboard
2. Main programs
3. Responsibilities
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1. Reading from the keyboard
There are a few ways – we will use Scanner
Essentials are:
import java.util.*;
…..
Scanner in=new Scanner(System.in);
…….
System.out.print("enter license: ");
license=in.nextLine();
…..
System.out.print("enter year: ");
year=in.nextInt();
in.nextLine(); //after a nextInt()
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Scanner is a builtin java class
• Check out the ‘API’ at:
http://docs.oracle.com/javase/7/docs/api/
• This looks like the documentation we had for
BJBeetle (called javadoc) – and it is
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2. Main program
• A main responsibility is to ‘run’ a whole
software system
• This is done from a special method associated
with the class not the objects (static):
public static void main(String args[]) {
//Fill in in a minute
}
5
Suppose we have a Clock with 2 Times
myClock
alarm
time
hrs 8
mins 30
hrs 10
mins 21
6
Here is the Class diagram (code in 2-week2-clock)
code on next slide – just look at column 1 first
Time
---------------------int hrs
-int mins
--------------------+Time ()
+void setTime(int h, int m)
+String toString()
2..2
Clock
---------------------Time alarm
-Time time
-boolean isSet
--------------------+Clock()
+setTime(int h, int m)
+setAT(int h, int m)
+void turnOnAlarm()
+void turnOffAlarm()
+boolean isAlarmRinging() //too hard
+String toString()
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public class Clock{ //horrible formatting to fit
private Time alarm; private Time time;
boolean isSet;
public class Time{
private int hrs;
private int mins;
public Clock(){
alarm=new Time(); time=new Time();
isSet=false;}
public Time() {
hrs=1;
mins=0;
}
public setTime(int h, int m){
time.setTime(h,m); }
public setAT(int h, int m){
alarm.setTime(h,m); }
public void turnOnAlarm(){
isSet=true; }
public void turnOffAlarm(){
isSet=true;}
public void setTime(int h, int m) {
hrs=h;
mins=m;
}
public String toString() {
return hrs+" : "+mins;
}
public String toString(){
if (isSet) {
return "time is "+time.toString()+" and alarm is set to "+alarm.toString();
}
}
else {
return "time is "+time.toString()+" ad alarm is off";
}
}
}
Mess around with the Time and
Clock classes
• You can exercise the methods
• Using a UseThis class you can even put those
method calls in a main() but it is all a bit adhoc
• Instead we create an Application type of class
and then run it in a main
• Look at RunClock.java
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• Do that – create a RunClock object (code next)
• And then call its runApplication() method
Now put these two things in the main:
public static void main(String args[]) {
RunClock clock=new RunClock();
clock.runApplication();
}
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Now when you run the main
• You are running those two methods!
• You can run from the command line with
java RunClock
• (incidentally you can bypass BlueJ by typing
javac *.java
to compile)
• You can actually have a class with nothing in it
but a main (see Main.java) or put the main in
the application class (RunClock for this example)
• It is good practice to have a small main program
Note – shows up under class
static things belong to the class
Not ‘event-driven’ programming
•
•
•
•
A loop asks the user what to do
The user answers
This is NOT …
….event-driven, which sits passively and waits
until the user does something (GUIs usually
are)
• We’ll do that next term
3. Responsibilities
• Our first examples were mostly about storing
information – methods used are:
constructors, gets, sets, toString, readKeyboard
• That’s fine but we need more!
• The runApplication() method started to show you
how objects have responsibilities to DO something
• More next week on this and main programs
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How do you know?
What instance variables to put in?
think about what each object of that class HAS
every clock has 2 times and is either set or not
Complex things deserve their own classes
Monsters have a name (simple String) but also a Weapon,
but that is complex so you need a Weapon class
What methods to write?
these are the RESPONSIBILITIES of objects of that class What they DO – Monsters wail for instance
It’s the class diagrams that are the hardest part! Once
the diagram is done the code is easy