1.Reading from Keyboard 2.Main programs 3.Responsibilities 1 CS12230 Introduction to Programming Lecture 2or3-Other things

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() 2

Scanner is a builtin java class Check out the ‘API’ at: This looks like the documentation we had for BJBeetle (called javadoc) – and it is 3

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 alarm time myClock 6 hrs 8 mins 30 hrs 10 mins 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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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 10

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 17

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