1. Reading from Keyboard2. Main programs 3. Responsibilities 1

CS12230Introduction to Programming

Lecture 2or3-Other things

1. Reading from the keyboard

There are a few ways – we will use ScannerEssentials 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

}

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Suppose we have a Clock with 2 Times

alarm

time

myClock

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hrs 8mins 30

hrs 10mins 21

Here is the Class diagram (code in 2-week2-clock)code on next slide – just look at column 1 first

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()

Time----------------------int hrs-int mins---------------------+Time ()+void setTime(int h, int m)+String toString()

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2..2

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public class Time{ private int hrs; private int mins; public Time() { hrs=1; mins=0; } public void setTime(int h, int m) { hrs=h; mins=m; } public String toString() { return hrs+" : "+mins; }}

public class Clock{ //horrible formatting to fit private Time alarm; private Time time; boolean isSet; public Clock(){ alarm=new Time(); time=new Time(); isSet=false;} 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 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 ad-hoc

• 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 classstatic 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 HASevery clock has 2 times and is either set or not

Complex things deserve their own classesMonsters 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