Java 5

1
Java 5 Tiger

• Short history.
• Where AP is headed likely features that will end
  up in the subset.
• Other fun features to use if you choose

2
Short History

• Java 1.1 to 1.2 had some language changes
• From 1.2 until Java 5, essentially no language
  feature changes just additions to the APIs
• Java 5 Tiger (originally called 1.5 during
  beta) now has many additional language features
• AP will adopt a couple

3
Generics

• Like templates in C
• Pedagogically, this is more sound. Lets declare
  to the compiler upfront what were going to put
  in if a student doesnt, shell get a compiler
  error. The old way, the runtime environment would
  discover that someone didnt put the right thing
  in/out and throw a run-time exception less
  desirable harder for students. Also, this is
  now self-documenting.
• ArrayListltFishgt list new ArrayListltFishgt()
• list.add( new Fish() )
• Fish f list.get(0)

Realize that one could put a Fish or any subclass
of Fish into this list. One could also choose to
put an interface or abstract class type within
the ltgt
4
Auto-Boxing/Unboxing

• Automatically put primitives into Wrapper classes
  and go other way as well. Works for all 8
  primitive types and their respective Wrapper
  class.
• Integer intObj 1
• int x intObj
• Yes! Nice!
• int answer intObj x

5
More generic Generics examples(sorry)

• Lets keep track of how many of each color crayon
  we have
• MapltString, Integergt crayons
• new TreeMapltString, Integergt()
• crayons.put(red, 1)
• crayons.put(blue, 2)
• int count crayons.get("blue")
• count
• crayons.put("blue", count)

6
Your Turn!

• Declare a structure that would allow you to keep
  a list of teacher names (wed eventually like to
  print them in alpha) who have a particular color
  crayon(wed like the crayon colors to also come
  out in alpha order)
• Red crayon ? Don, Sharon, Joe, Mike
• Blue crayon ? Kent, Doug, Dan, Carol
• Green crayon ? Harlie, Jennifer, Gerard
• Yellow crayon ? Mark, Sam, Kevin, Norm
• Orange crayon ? Shirley, Regina, Dave, Jon
• (you have 10 minutes go try get all the names
  in and then print)

7
Heres one way

• MapltString, SetltStringgtgt crayons new
  TreeMapltString, SetltStringgtgt()
• Set s new TreeSet()
• s.add("Don")
• s.add("Sharon")
• s.add("Joe")
• s.add("Mike")
• crayons.put("red",s)
• s new TreeSet()
• s.add("Kent")
• s.add("Doug")
• s.add("Dan")
• s.add("Carol")
• crayons.put("blue",s)
• System.out.println(crayons)

8
What will AP do?

• So, AP will probably adopt Generics and
  Auto-boxing/unboxing for the 07 exam
• No official word yet but its almost for sure
• May or may not adopt the For each loop
• Leads to cleaner questions so probably

9
For Each loop

• Fish fishes
• for (Fish f fishes)
• f.act()
• Pros no OBOBs cleaner
• Cons cant skip 1st, last, increment some index,
  delete an element

10
more For Each

• ArrayListltFishgt fishList
• for (Fish f fishList)
• f.act()

11
more For Each

• int nums 1,2,3,4,5
• for (int x nums)
• System.out.println(x)

12
more For Each

• public static void setsAreIterable()
• SetltIntegergt s
• new TreeSetltIntegergt()
• s.add(1)
• s.add(2)
• s.add(3)
• for (int x s)
• System.out.println( x )

13
more For Each

• In general, any class that implements Iterable
  will allow you to use the For Each loop

14
AP Probably Wont adopt

• Scanner
• Variable number of parameters

15
Scanner

• // from console
• Scanner in new Scanner(System.in)
• System.out.print("How old are you?")
• int age in.nextInt()
• // from file
• String fileName . . .
• Scanner file new Scanner(new File(fileName))
• Easy no more third-party packages necessary

16
Variable number of parameters

• public static double average(double... values)
• assert values.length gt 0
• double sum 0
• for (double v values)
• sum v
• return sum / values.length

17
For more

• See apcentral.collegeboard.com