Java

5.0

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 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

Java

5.0

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.

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 <>

Java

5.0

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;

Java

5.0More generic Generics examples

(sorry)

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);

Java

5.0

Your Turn!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)

Java

5.0

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);

s = new TreeSet(); s.add("Kent"); s.add("Doug"); s.add("Dan"); s.add("Carol"); crayons.put("blue",s); System.out.println(crayons);

Java

5.0

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));

Easy – no more third-party packages necessary

Java

5.0

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