Deadlines

1
02-17

• Deadlines
• Assignment 5 due Thursday 2/17, 415PM
• deadline for 5 extended to Tuesday 2/22
• Assignment 6 Assigned 2/18, due 3/1
• Second midterm exam Thursday 2/24
• Last time
• major components of input loops
• input verification versus user input stream
  versus file input stream
• what operation on the stream
• do something to every record
• accumulate information about all the records
• sum/count, min/max, any/every
• combinations of the above
• This time
• a little review
• loop over sequences
• nested loops
• collections, positional access, and the Iterator
  interface

2
Loop Mechanics

• Establish the input stream
• in the case of user input, establish how you want
  to stop and whether you will allow no input at
  all

InputUtilities iu new InputUtilities() //
maybe some initialization here while (true)
String nextInput iu.getLine("Next input ")
if (stopIndicator(nextInput)) break
doSomethingToInput(nextInput) // maybe some
output here
InputUtilities iu new InputUtilities() //
maybe some initialization here boolean moreInput
true while (moreInput) String nextInput
iu.getLine("Next input ") doSomethingToInput(n
extInput) moreInput iu.getYestNo("More
input? ") // maybe some output here
3
Don't Be Fooled By Small Variations in Form
InputUtilities iu new InputUtilities() //
maybe some initialization here while (true)
String nextInput iu.getLine("Next input ")
doSomethingToInput(nextInput) if
(!iu.getYesNo("More input? ")) break //
maybe some output here
InputUtilities iu new InputUtilities() //
maybe some initialization here boolean moreInput
true while (moreInput) String nextInput
iu.getLine("Next input ") doSomethingToInput(n
extInput) moreInput iu.getYesNo("More
input?") // maybe some output here
non-local exit versus sentinel is a matter of
style prompting for more input versus input
termination value is an important design decision
4
Another Small Variant While versus Until
int sum 0 do sum iu.getInt("Next
input ") while (iu.getYesNo("More input? "))
int sum 0 while (iu.getYesNo("More input? "))
sum iu.getInt("Next input ")
5
Loop Mechanics for File Input
Scanner scf new Scanner(new File(FILE_NAME)) /
/ maybe some initialization here while
(scf.hasNext()) String nextToken
(String)scf. next() doSomethingToToken(nextToke
n) // always need to handle possibility of no
input
Scanner scf new Scanner(new File(FILE_NAME)) /
/ maybe some initialization here while
(scf.hasNextLine()) String nextLine scf.
nextLine() doSomethingToLine(nextLine) //
always need to handle possibility of no input
Whether or not to do line-oriented or
token-oriented processing is a major design
decision. Loop control is essentially the same
in either case.
6
Next Choose Your Processing Idiom
int sum 0 while (scf.hasNext()) int
nextNumber scf.nextInt() sum
nextNumber // postcondition variable sum
// holds result
int max Integer.MIN_VALUE if (!scf.hasNext())
// maximum not defined reportBadMaximum()
else while (scf.hasNext()) int
nextNumber scf.nextInt() max
Math.max(nextNumber, max) // postcondition
variable max holds // result unless no input
boolean every true while (scf.hasNext())
Object nextThing scf.next() if
(!propertyHoldsFor(nextThing)) every
false break // postcondition
variable every // holds result
7
Overall Lesson About Input Stream Processing

• Role of the loop structure is (only) to control
  when to quit
• Type of input (file or console, token or line)
  determines the input idiom
• Type of processing task (calculate and output,
  accumulate) determines the processing idiom
• When designing new code, think of these decisions
  in isolation, not as part of one big mess!