Download Java 5 – Tiger - AP Computer Science

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
Java 5.0
Short History
Java 5.0
• 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
Generics
• Like “templates” in C++
• Pedagogically, this is more sound. Let’s declare to
the compiler upfront what we’re going to put in – if a
student doesn’t, she’ll get a compiler error. The old
way, the runtime environment would discover that
someone didn’t put the right thing in/out and throw
a run-time exception – less desirable – harder for
students. Also, this is now self-documenting.
Java 5.0
ArrayList<Fish> list =
new ArrayList<Fish>();
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 <>
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!
Java 5.0
int answer = intObj + x;
More generic Generics examples
(sorry)
Java 5.0
Let’s keep track of how many of each color
crayon we have…
Map<String, Integer> crayons =
new TreeMap<String, Integer>();
crayons.put(“red”, 1);
crayons.put(“blue”, 2);
…
int count = crayons.get("blue");
count++;
crayons.put("blue", count);
Your Turn!
Java 5.0
Declare a structure that would allow you to keep a list of
teacher names (we’d eventually like to print them in
alpha) who have a particular color crayon(we’d 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)
Here’s one way
Map<String, Set<String>> crayons =
new TreeMap<String, Set<String>>();
Set s = new TreeSet();
s.add("Don");
s.add("Sharon");
s.add("Joe");
s.add("Mike");
crayons.put("red",s);
Java 5.0
s = new TreeSet();
s.add("Kent");
s.add("Doug");
s.add("Dan");
s.add("Carol");
crayons.put("blue",s);
System.out.println(crayons);
What will AP do?
• So, AP will probably adopt Generics and
Auto-boxing/unboxing for the ’07 exam
– No official word yet – but it’s almost for sure
• May or may not adopt the “For each” loop
– Leads to cleaner questions – so probably
Java 5.0
“For Each” loop
Fish[] fishes = …;
for (Fish f : fishes)
f.act();
Pros: no OBOB’s – cleaner
Cons: can’t skip 1st, last, increment
some index, delete an element
Java 5.0
more For Each…
ArrayList<Fish> fishList = …;
for (Fish f : fishList)
f.act();
Java 5.0
more For Each…
int[] nums = {1,2,3,4,5};
for (int x : nums)
System.out.println(x);
Java 5.0
more For Each…
public static void setsAreIterable()
{
Set<Integer> s =
new TreeSet<Integer>();
s.add(1);
s.add(2);
s.add(3);
for (int x : s)
System.out.println( x );
}
Java 5.0
more For Each…
• In general, any class that implements
Iterable will allow you to use the “For
Each” loop
Java 5.0
AP Probably Won’t adopt…
• Scanner
• Variable number of parameters
Java 5.0
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));
Java 5.0
Easy – no more third-party packages necessary
Variable number of parameters
public static double average(double... values)
{
assert values.length > 0;
double sum = 0;
for (double v : values)
sum += v;
return sum / values.length;
Java 5.0
}
For more…
• See apcentral.collegeboard.com
Java 5.0