CS100J, Spring 2001
Thurs 9/27
Lecture 9
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Announcements:
+ give Alan any waivers and Project1s that need submission
+ P3 due Thurs 10/4
+ T1: on Mon 10/1
  - Details (incl rooms): Exams-->Prelim 1
  - Review session: Exams-->Review 1
+ comprehensive makeup project will cover one missed project 
  - see 9/25 Announcements online
+ MATLAB: See Announcements
+ actually, all of this was already announced on Announcements :-)
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Topics:
+ commenting a method
+ method arguments
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Commenting:
+ brief: describe action of method above the header
+ longer: see pp 243-244, App.4 on pg 993 for an example
  - Precondition: what's true before the method is invoked
  - Action: what the method does
  - Postcondition: what's true after the method is invoked
+ action and postcondition are sometimes the same thing
+ sometimes it's clearer to just write the action
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Arguments:
+ arguments are variables that receive values and are used in method body
+ Java is strongly typed
+ arguments is composed of series of inputs with form:
  type1 var1, type2 var2, ...
+ can also have NO arguments
  ex) System.out.println(), which prints a blank line
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Terminology:

+ Formal parameters:
  - variables written inside method header
  - born when method invoked
    live during method execution
    die when method ends

+ Actual parameters:
  - anything passed into a method

+ Local variables:
  - variables declared inside a method
  - same rules as formal parameters
  - variables cannot be "seen" (are invisible) to other methods	
    + think "statement block": header { stuff; } 
    + the "stuff" may have declarations which are local (visible)
      only in the block!

+ Call by value:
  - value of actual parameter copied into formal parameter
  - method can NOT change the value of an actual parameter

+ Scope:
  - the visibility of a element of code (variable, method)
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Example:

  public class Example2 { 
     public static void myPrint(String s, int x) {
        System.out.println(s+" is "+x);
     } 

     public static int myRandom(int x) {
        int y = 1;
	return (int)( Math.random()*(x+y) );
     }

     public static void main(String[] args) {
	int x = 10;
	int y = myRandom(x);
	myPrint(x);
	myPrint(y);
     }
  }     
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Example:   

  public class Example3 { 

     public static void warning(int x) {
        if (x != 0) {
	   System.out.println("Buh!");
	   return;
	else
  	   System.out.println("OK!");
     }

     public static void main(String[] args) {
        warning( (int) Math.random()*2 );
	System.out.println("yo!");
     }
  }     
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